cardanol: a bio-based building block for new sustainable

1

Ecole Doctorale Science et Ingénierie

De l’Université de Cergy-Pontoise

THESE

Pour obtenir le grade de docteur de l’Université de Cergy-Pontoise

Spécialité: Chimie des matériaux

Cardanol: a bio-based building block for new

sustainable and functional materials

Présentée par

Laura Puchot

Laboratoire de Physico-chimie des Polymères et des Interfaces, EA 2528

Soutenue le 14 décembre 2016 devant le jury composé de :

Etienne Fleury, Professeur à l’INSA de Lyon Rapporteur

Florent Allais, Professeur à AgroParis Tech de Reims Rapporteur

Naceur Belgacem, Professeur à l’INP-Pagora de Grenoble Président du jury

Valérie Langlois, Professeur à l’Université Paris Est Créteil Examinateur

Frédéric Vidal, Professeur de l’Université de Cergy-Pontoise Directeur de thèse

Cédric Vancaeyzeele, Maître de conférences de l’Université de Cergy-Pontoise Co-encadrant

Pierre Verge, Ingénieur de recherche à LIST Co-encadrant

Youssef Habibi, Ingénieur de recherche à LIST Co-encadrant

René Saint Loup, Responsable département chimie des polymères chez Roquette Invité

2

Abstract

Recently, considerable interest of the chemistry of renewable ressources and their resulting

materials has grown with a view to reduce the use of finite petroleum-based resources. The

present thesis entitled « Cardanol: a bio-based building block for new sustainable and

functional materials » is dealing with the chemical modification of cardanol and its use for

various applications. Cardanol is a naturally occurring phenolic compound issued from cashew

nutshell liquid. Its chemical structure is interesting because cardanol is bearing a phenolic

hydroxyl function and an unsaturated alkyl chain in meta. Numerous chemical reactions can thus

be considered for its chemical modification.

The first part of this study is dealing with the synthesis and the characterization of three cardanol-

based ammonium surfactants differing by their amine functionalities content. Their effectiveness

on the exfoliation of silicate clay within an epoxy matrix was investigated with the aim to

elaborate composite materials.

The second chapter is describing a novel method for the synthesis of bio-based benzoxazine

monomers and the elaboration of polybenzoxazine networks issued from cardanol. A new

generation of benzoxazine monomers issued from cardanol or from lignin derivatives such as

vanillin were recently developed. However, up to now, the majority of the synthetised

benzoxazine monomers are mainly mono-functionnal or display too high melting temperatures.

The elaboration of valuable self-standing materials is thus strongly impeded. To solve this

problem, an innovative synthesis of asymmetric benzoxazine monomers by combination of

cardanol and lignin derivatives is described. The resulting self-standing materials display

improved properties in comparison to materials issued from symmetric bio-based monomers.

Finally, the third chapter realtes to the use of a cardanol-based epoxy pre-polymer for the

elaboration of bio-based epoxy materials. Nevertheless, this new material displays low Tg due to

the alkyl side chain of cardanol in addition to low water uptake. In order to reinforce the thermo-

mechanical properties of the material and to reduce its water uptake, a chemical modification

was achieved at the macromolecular scale by the elaboration of interpenetrating polymer

networks with polybenzoxazine networks.

These various studies allowed to highlight the easy and versatile modification of cardanol,

resulting thus in a diversity of bio-based synthons and their resulting materials. This work paves

the way to the elaboration of other chemical structures and molecular architectures for various

applications.

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Résumé:

Récemment, la chimie des ressources renouvelables et les matériaux qui en découlent ont suscités

un intérêt considérable dans le but de limiter l’utilisation des ressources fossiles. La présente

thèse intitulée « Cardanol : a bio-based building block for new sustainable and functional

materials » traite de la modification chimique du cardanol et de son utilisation dans diverses

applications. Le cardanol est un dérivé phénolique naturel extrait de l’huile de coque de noix de

cajou. Sa structure chimique est intéressante : il est substitué d’une chaîne alkyle en C15,

partiellement insaturée, et il est porteur d’une fonction phénol, permettant d’envisager de

nombreuses réactions chimiques.

La première partie de cette étude traite de la synthèse et de la caractérisation de trois surfactants

ammoniums issus du cardanol se différenciant par le degré de substitution de leurs amines. Leur

capacité à favoriser l’exfoliation d’une argile lamellaire dans une matrice de type époxy a été

étudiée dans le but de concevoir des matériaux composites.

Le second chapitre décrit une nouvelle méthode de synthèse de monomères benzoxazines bio-

basés et l’élaboration de réseaux polybenzoxazines à partir du cardanol. Une nouvelle génération

de monomères benzoxazine, issus du cardanol ou de dérivés de la lignine tels que la vanilline, a

récemment été développée. Cependant l’essentiel des benzoxazines bio-basées synthétisées

jusqu’à présent sont monofonctionnelles ou présentent des températures de fusion trop élevées.

Elles ne permettent donc pas l’élaboration de matériaux autosupportés valorisables. Afin de

pallier ce problème, une synthèse originale de monomères benzoxazines asymétriques, reposant

sur la combinaison de cardanol et de dérivés de la lignine, est décrite. Les matériaux

autosupportés résultants présentent des propriétés améliorées par rapport à celles que ne

pourraient atteindre les monomères symétriques issus de ces phénols bio-sourcés.

Finalement, le troisième chapitre concerne l’utilisation d’un pré-polymère époxy issu du cardanol

pour l’élaboration de matériaux époxy bio-basés. Cependant, ce nouveau matériau présente une

faible Tg en raison de la chaîne alkyle du cardanol et une faible prise en eau. Afin de renforcer ses

propriétés thermo-mécaniques et de diminuer sa prise en eau, une modification chimique a été

réalisée à l’échelle macromoléculaire par l’élaboration de réseaux interpénétrés de polymères à

base de réseaux polybenzoxazines.

Ces différents travaux ont permis de mettre en avant la modification aisée et versatile du

cardanol, pouvant ainsi résulter en une large variété de synthons bio-basés et des matériaux qui

en découlent. Ces travaux ouvrent la voie vers d’autres structures et architectures moléculaires

aux applications nombreuses.

4

Remerciements

J’adresse mes sincères remerciements au Professeur Frédéric Vidal, directeur du Laboratoire de

Physico-Chimie des Polymères et des Interfaces, pour son accueil au sein de son laboratoire afin de

réaliser mes travaux de thèse et pour son encadrement durant ces trois années.

Je tiens à remercier particulièrement Docteur Pierre Verge pour son encadrement de tous les jours

au sein du Luxembourg Institute of Science and Technology, pour son soutien, sa disponibilité, son

aide et ses conseils tout au long de ma thèse. Je remercie également les Docteurs Cédric Vancaeyzeele

et Youssef Habibi pour leur implication dans ces travaux et pour leur support.

Je souhaite exprimer ma reconnaissance aux membres du jury de thèse, Pr. Etienne Fleury, Pr.

Florian Allais, Pr. Valérie Langlois, Pr. Naceur Belgacem et Dr. René Saint-Loup, d’avoir accepté

d’évaluer ce travail.

Je souhaite égalament remercier tous les membres du département matériaux au sein du LIST,

passés et présents, pour l’aide et le soutien qu’ils m’ont apporté. Je remercie tout particulièrement

mes collègues et les anciens doctorants ainsi que les nouveaux pour leur bonne humeur et les

agréables moments passés avec eux aussi bien au laboratoire qu’en dehors.

Je tiens aussi à remercier tous les membres du LPPI pour leur accueil chaleureux à chacune de mes

visites. Je les remercie également pour leur aide et leurs conseils.

Enfin je remercie infiniment mes parents, Christophe et Michaele, ma sœur, Julia, et mon conjoint,

Habib, pour leur soutien durant ces années.

5

Contents

List of Abbreviations ................................................................................................................................... 10

List of Figures ................................................................................................................................................. 13

List of Tables .................................................................................................................................................. 20

General Introduction and Context .......................................................................................................... 22

Chapter I: Introduction ............................................................................................................................... 25

1 Cashew nutshell liquid: extraction and composition ............................................................. 25

2 Extraction of cardanol from CNSL and reactivity ..................................................................... 27

3 Cardanol based chemicals and functional molecules ............................................................. 30

3.1 Plasticizers and reactive diluents ........................................................................................................ 30

3.2 Surfactants .................................................................................................................................................... 32

3.2.1 Anionic surfactants .......................................................................................................................... 33

3.2.2 Non-ionic surfactants ...................................................................................................................... 35

3.2.3 Cationic surfactants ......................................................................................................................... 36

3.3 Curing agents ............................................................................................................................................... 37

3.4 Antioxidant ................................................................................................................................................... 40

4 Cardanol-based polymers ................................................................................................................. 42

4.1 Phenolic resins ............................................................................................................................................ 43

4.2 Polyurethane resins .................................................................................................................................. 44

4.2.1 Synthesis of cardanol-based polyols ........................................................................................ 44

4.2.2 Cardanol-based non-isocyanate PU .......................................................................................... 48

4.3 Epoxy resins ................................................................................................................................................. 49

4.4 Polybenzoxazine resins ........................................................................................................................... 51

5 Conclusion .............................................................................................................................................. 52

Chapter II: Surfactants from cardanol .................................................................................................. 53

1 Introduction........................................................................................................................................... 53

1.1 Preparation of nanocomposite materials ......................................................................................... 53

1.2 Structure and properties of clay and layered silicates as fillers ............................................. 54

1.3 Clay organomodification strategies .................................................................................................... 57

1.3.1 Clay organomodification by cationic exchange reaction .................................................. 57

1.3.2 Clay organomodification by cationic exchange reaction and covalent grafting ..... 59

6

1.4 Cationic surfactants from Cardanol .................................................................................................... 60

2 Results and discussion ....................................................................................................................... 62

2.1 Surfactants synthesis ................................................................................................................................ 62

2.2 Characterization of CardSx surfactants ............................................................................................. 63

2.2.1 Fourier Transform Infrared spectroscopy (FTIR) .............................................................. 63

2.2.2 Characterization by 1H NMR ........................................................................................................ 64

2.2.3 Characterization by MALDI-TOF/MS ....................................................................................... 69

2.3 MMT clay organomodification and characterization .................................................................. 72

2.3.1 O-MMT preparation procedure .................................................................................................. 72

2.3.2 Characterization of O-MMT by X-ray diffraction (XRD) ................................................... 72

2.3.3 Characterization of O-MMT by MALDI-TOF/MS .................................................................. 73

2.4 Evidence of the surfactant amino-multifunctionnality within MMT clay ........................... 75

2.5 Preparation and characterization of CPN materials .................................................................... 77

2.5.1 CPN preparation procedure ......................................................................................................... 77

2.5.2 CPN characterization by X-ray diffraction (XRD) ................................................................ 78

2.5.3 CPN Thermal characterisation .................................................................................................... 79

2.5.4 CPN characterization by SEM and EDX analyses ................................................................. 82

3 Conclusions ............................................................................................................................................ 83

Chapter III: Benzoxazines from cardanol ............................................................................................ 85

1 Introduction........................................................................................................................................... 85

1.1 Benzoxazine thermosets ......................................................................................................................... 85

1.1.1 Generalities ......................................................................................................................................... 85

1.1.2 Benzoxazine polymerization ....................................................................................................... 87

1.1.3 Effect of hydrogen bonding and π-π supramolecular interactions on

polybenzoxazines properties .......................................................................................................................... 89

1.1.4 Polymerization catalysis ................................................................................................................ 91

1.1.5 Focus on di-benzoxazine monomers ........................................................................................ 93

1.2 Synthesis of Class B benzoxazines ...................................................................................................... 94

1.2.1 Electron donating and withdrawing effect ............................................................................ 94

1.2.2 Flexibility of the bridging diamine ............................................................................................ 94

1.3 Thermal properties of Class B di-Bz monomers and PBz resins ............................................ 95

1.3.1 Flexibility and chain length of the bridging diamine ......................................................... 95

1.3.2 Additional functional groups ....................................................................................................... 98

1.4 Bio-based benzoxazine: State of the art ........................................................................................... 99

1.4.1 Vanillin ................................................................................................................................................ 100

1.4.2 Guaïacol .............................................................................................................................................. 104

7

1.4.3 Lignin-derivatives .......................................................................................................................... 104

1.4.4 Eugenol ............................................................................................................................................... 107

1.4.5 Coumarin ............................................................................................................................................ 109

1.4.6 Cardanol ............................................................................................................................................. 110

1.4.7 Urushiol .............................................................................................................................................. 113

1.5 Asymmetric benzoxazine monomers............................................................................................... 115

1.5.1 State of the art .................................................................................................................................. 115

2 Results and discussion .................................................................................................................... 117

2.1 Symmetric benzoxazine monomers synthesis and characterization ................................. 118

2.1.1 Symmetric Bz monomer synthesis .......................................................................................... 118

2.1.2 Characterization by 1H NMR ...................................................................................................... 118

2.1.3 Characterization by MALDI-TOF/MS or HRMS .................................................................. 124

2.1.4 Characterization by DSC and TGA............................................................................................ 127

2.1.5 Characterization by rheology analysis ................................................................................... 130

2.2 Asymmetric benzoxazine monomers synthesis and characterization............................... 132

2.2.1 Asymmetric Bz monomer synthesis ....................................................................................... 132

2.2.2 Characterization by 1H NMR ...................................................................................................... 133

2.2.3 Characterization by MALDI-TOF/MS ..................................................................................... 136

2.2.4 Characterization by DSC .............................................................................................................. 138

2.2.5 Characterization by rheology analysis ................................................................................... 139

2.3 Materials elaboration and characterizations ................................................................................ 141

2.3.1 Materials elaboration .................................................................................................................... 141

2.3.2 DMA characterization ................................................................................................................... 141

3 Conclusions ......................................................................................................................................... 143

Chapter IV: Interpenetrating Polymer Networks (IPN) from a cardanol-based thermoset

network ......................................................................................................................................................... 146

1 Introduction........................................................................................................................................ 146

1.1 Cashew nutshell diglycidyl ether ....................................................................................................... 147

1.2 CDGE-based thermosets ........................................................................................................................ 149

1.3 Reinforcement strategies: macromolecular reinforcement of epoxy networks ............ 152

1.3.1 State of the art of the epoxy/benzoxazine based co-networks ................................... 152

1.4 Epoxy/polybenzoxazine IPNs ............................................................................................................. 154

2 Results and discussion .................................................................................................................... 158

2.1 Choice of the system ............................................................................................................................... 158

2.1.1 Sequential in-situ preparation of IPN ..................................................................................... 158

2.1.2 Determination of the Bz monomer .......................................................................................... 159

8

2.1.3 Determination of the suitable di-amine hardener ............................................................ 160

2.2 Curing profile for the elaboration of poly(CDGE)/poly(EDBz) IPNs .................................. 163

2.2.1 First step curing .............................................................................................................................. 164

2.2.2 Full curing profile ........................................................................................................................... 166

2.3 Poly(CDGE)/poly(EDBz) IPNs ............................................................................................................ 166

2.3.1 Poly(CDGE)/poly(EDBz) IPN Material elaboration .......................................................... 166

2.3.2 Thermo-mechanical properties of IPN materials .............................................................. 167

2.3.3 Estimation of the morphology by theoretical models ..................................................... 170

2.3.4 Behaviour toward water exposure ......................................................................................... 172

3 Conclusion ........................................................................................................................................... 174

General Conclusion and Perspectives ................................................................................................ 177

Annex: Materials and Methods ............................................................................................................. 180

1 Chapter II: Surfactants from cardanol ....................................................................................... 180

1.1 Materials ...................................................................................................................................................... 180

1.2 Characterization methods .................................................................................................................... 180

1.2.1 NMR analysis .................................................................................................................................... 180

1.2.2 Mass analysis .................................................................................................................................... 180

1.2.3 XRD analysis ..................................................................................................................................... 181

1.2.4 SEM analyis ....................................................................................................................................... 181

1.2.5 DSC analysis ...................................................................................................................................... 181

1.3 Surfactant synthesis ................................................................................................................................ 181

1.3.1 Synthesis and purification of CardS1 ..................................................................................... 181



1.4 MMT clay organomodification ............................................................................................................ 183

1.5 Reaction of the intercalated surfactants with Fge ...................................................................... 183

1.6 Clay mineral-based polymer nanocomposite (CPN) preparation ........................................ 183

2 Chapter III: Benzoxazines from cardanol ................................................................................ 183

2.1 Materials ...................................................................................................................................................... 183


2.2.1 NMR analysis .................................................................................................................................... 184

2.2.2 Mass analysis .................................................................................................................................... 184

2.2.3 DSC analysis ...................................................................................................................................... 184

2.2.4 Rheology analysis ........................................................................................................................... 185

2.2.5 DMA analysis .................................................................................................................................... 185

9

2.2.6 TGA analysis ..................................................................................................................................... 185

2.3 Synthesis of the Bz monomers ............................................................................................................ 185

2.3.1 Synthesis of the di-cardanol Bz monomer ........................................................................... 185

2.3.2 Synthesis of the di-vanillin Bz monomer .............................................................................. 186

2.3.3 Synthesis of the di-phenol Bz monomer ............................................................................... 186

2.3.4 Synthesis of the Vani-Card asymmetric Bz monomer ..................................................... 186

2.4 Material elaboration ............................................................................................................................... 187

3 Chapter IV: Interpenetrating Polymers Networks (IPN) from cardanol-based

thermoset networks ................................................................................................................................. 187

3.1 Materials ...................................................................................................................................................... 187


3.2.1 DSC analysis ...................................................................................................................................... 187

3.2.2 Solvent extraction........................................................................................................................... 187

3.2.3 DMA analysis .................................................................................................................................... 188

3.3 Material elaboration ............................................................................................................................... 188

Annex: Figures ............................................................................................................................................ 189

References .................................................................................................................................................... 191

10

List of Abbreviations

AAF Available Amino Functionalities

BADGE Bisphenol A Diglycidyl Ether

BTH Butyl Hydroxyl Toluene

Bz Benzoxazines

CA Coumaric Acid

CDGE Diglycidyl Ether of Cardanol

CEC Cation Exchange Capacity

CHCA α-cyano 4-hydroxycinnamic acid

CMC Critical Micelle Concentration

CNSL Cashew Nutshell Liquid

CNT Carbon Nanotubes

CPN Clay mineral-based polymer nanocomposite

DAC Diaminocyclohexane

DCTB Trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile

DDBS Dodecylbenzene Sulfonate

DDM 4,4’-diaminodiphenyl methane

DEHP Di-Ethyl-Hexyl-Phtalate

DETA Diethylenetriamine

di-Bz Di-Benzoxazine Monomers

DMA Dynamic Mechanical Analysis

DMEDA N,N-dimethylethylenediamine

DOP Dioctyl Phthalate

DSC Differential Scanning Calorimetry

DTA Differential Thermal Analysis

EC Extracted Content

EDA Ethylene Diamine

EDX Energy Dispersive X-Ray Analysis

EEW Epoxy Equivalent Weight

FA Ferulic Acid

Fge Furfuryl Glycidyl Ether

11

FTIR Fourier Transform Infrared Spectroscopy

HAD Hexamethylenediamine

HRMS High Resolution Mass Spectrometry

IPD Isophorone Diamine

IPN Interpenetrating Polymer Network

MALDI Matrix-Assisted Laser Desorption/Ionization

m-Bz Mono-Benzoxazine Monomers

MLO Mineral Lubricant Oil

MMT Montmorillonite

MS Mass analysis

MS/MS Tandem Mass Spectrometry

NMR Nuclear Magnetic Resonance Spectroscopy

O-MMT Oragnomodified Montmorillonite

PA Phloretic Acid

PANI Polyaniline

PBz Polybenzoxazine

PMMA Poly(methyl methacrylate)

POSS Polyhedral Oligomeric Silesquioxanes

PU Polyurethanes

PVC Polyvinyl Chloride

ROP Ring-Opening Polymerization

SC Sulfonate Cardanol Surfactant

SDS Sodium Dodecyl Sulfonate

SEC Size Exclusion Chromatography

SEM Scanning Electron Microscopy

T5% 5 wt% Loss Temperature

TAEA Tris(2-aminoethyl)amine

Tamb Ambient Temperature

Tg Glass transition Temperature

TGA Thermogravimetric Analysis

Tm Melting Temperature

TOF Time-Of-Flight

12

Tp Polymerization Temperature

XRD X-Ray Diffraction

ΔTproc Processing Window

13

List of Figures

Figure 1. Global production capacities of bioplastics (In 2013 and forecast for 2018).2 ............... 22

Figure I - 1. Main cashew nut producing countries in 2012. ...................................................................... 25

Figure I - 2. Representation of cashew apples. ................................................................................................ 25

Figure I - 3. Cross section of a cashew nut and nutshell. ............................................................................. 26

Figure I - 4. Chemical structure of CNSL components a) anacardic acid, b) cardanol, c) cardol

and d) 2-methylcardol. ................................................................................................................................................ 26

Figure I - 5. Anacardic acid decarboxylation. ................................................................................................... 27

Figure I - 6. Average compositions of the cardanol alkyl side chain. ...................................................... 28

Figure I - 7. Representation of the possible chemical modifications on the three reactive sites of

cardanol. ............................................................................................................................................................................ 28

Figure I - 8. Fine chemicals and functional molecules from cardanol. ................................................... 29

Figure I - 9. Schematic representation of polymer matrix a) plasticizer-free and b) in presence

of a plasticizer. ................................................................................................................................................................ 30

Figure I - 10. Chemical structure of mono-epoxidized cardanol NC-513 from Cardolite. ............. 32

Figure I - 11. Chemical structures of cardanol polyepoxy derivatives plasticizers.18 ..................... 32

Figure I - 12. Schematic representation of the various types of surfactants a) cationic, b)

anionic, c) non-ionic and d) zwitterionic. ............................................................................................................ 33

Figure I - 13. Synthesis of cardanol sulfonate surfactants.30 ...................................................................... 34

Figure I - 14. Synthesis of cardanol diazonium sulfonate surfactant.44 ................................................. 34

Figure I - 15. Chemical structure of cardanol carbonate surfactant.45 ................................................... 34

Figure I - 16. Chemical structure of sulfonated acrylate cardanol surfactants a) sulfonated-3-

pentadecyl phenyl acrylate and b) sodium-2-acryloxy ethan-1-oxy(3-pentedecyl) benzene

sulfonate.47 ....................................................................................................................................................................... 35

Figure I - 17. Chemical structure of cardanol polyethoxylate surfactants.27, 48 .................................. 36

Figure I - 18. Chemical structure of cardanol quaternary ammonium salt surfactants.49 ............. 36

Figure I - 19. Synthesis of cardanol ammonium salt surfactants.51 ......................................................... 37

Figure I - 20. Synthesis of cardanol phenalkamine curing agent.52 ......................................................... 37

Figure I - 21. Chemical structure of phenalkamine component from a) hexamethylenediamine

and b) diethylenetriamine.55 ..................................................................................................................................... 38

Figure I - 22. Synthesis of phenalkamine compounds from cardanol with varying molecular

weight and amine content.56 ..................................................................................................................................... 38

14

Figure I - 23. Synthesis of cardanol-based phenalkamine compound by thiol-ene chemistry.16 39

Figure I - 24. Chemical structures of a) cardanol-cysteamine, and b) commercial NX-5454

phenalkamine. ................................................................................................................................................................. 40

Figure I - 25. Chemical structures of cardanol-based antioxidants. ....................................................... 40

Figure I - 26. Synthesis of cardanol-based phenolic resin.63 ...................................................................... 43

Figure I - 27. Condensation of cardanol with furfural and para-hydroxyacetophenone.66 ........... 43

Figure I - 28. Synthesis of a polyurethane. ........................................................................................................ 44

Figure I - 29. Chemical structures of cardanol-based diols a)72 b)73 c)69. ............................................. 45

Figure I - 30. Synthesis of cardanol-based polyol by reaction with oxazolidine.74 ........................... 45

Figure I - 31. Synthesis of cardanol-based polyols by reaction with melamine and di-

ethanolamine.75 .............................................................................................................................................................. 46

Figure I - 32. Synthesis of cardanol-based polyols by reaction with epichlorohydrin and

diethanol amine or with glycerol monochlorohydrin.73 ................................................................................ 46

Figure I - 33. Synthesis of cardanol-based polyols by performic acid oxidation.76 .......................... 47

Figure I - 34. Synthesis of cardano-based polyols by thiol-ene coupling with 2-

mercaptoethanol.77 ....................................................................................................................................................... 48

Figure I - 35. Synthesis of CNSL-based urethane polyols via a non-isocyanate route.78 ................ 49

Figure I - 36. Chemical structure of diglycidyl ether of cardanol – commercially available NC514

- from Cardolite Corporation. ................................................................................................................................... 49

Figure I - 37. Proposed reaction between epoxy groups of cardanol and carboxyl-terminated

polybutadiene.22 ............................................................................................................................................................. 50

Figure I - 38. Synthesis of epoxidized cardanol pre-polymer.25 ............................................................... 50

Figure I - 39. Synthesis of epoxidized cardanol and polycardanol. 80 .................................................... 51

Figure I - 40. Synthesis of a benzoxazine monomer.81 .................................................................................. 52

Figure II - 1. Schematic representation of a) MMT multi-scale organization,93 and b) MMT

crystallographic structure.89 ..................................................................................................................................... 55

Figure II - 2. Schematic representation of a) phase separated microcomposites, b) intercalated

nanocomposites, and c) exfoliated nanocomposites. ..................................................................................... 56

Figure II - 3. Schematic representation of the monomer inclusion within MMT, followed by in-

situ polymerization to reach MMT exfoliation. ................................................................................................. 58

Figure II - 4 Grafting of an amino-silane compound on prior organomodified MMT clay.108....... 60

Figure II - 5. Chemical structure of cardanol-based quaternary ammonium surfactant from De

Avellar et al.49 .................................................................................................................................................................. 60

15

Figure II - 6. Synthesis of cardanol-based ammonium surfactant from the cardanol mono-epoxy

derivative NC-513.51 ..................................................................................................................................................... 61

Figure II - 7. Scanning Electron Micrographs of BADGE/DAC polymer network filled with a) 5

wt% neat sepiolite and b) 5 wt% sepiolite organomodified by PkH+.51 ................................................. 61

Figure II - 8. Schematic representation of the synthesis of the Cardanol-based surfactants. ...... 63

Figure II - 9. FTIR spectra of a) CardS1, b) CardS2, c) CardS3................................................................... 64

Figure II - 10. CardS1 1H NMR spectrum (Solvent CDCl3). .......................................................................... 65



Figure II - 13. MALDI-MS spectra of CardS1 using a) CHCA & b) DCTB as matrix, CardS2 using c)

CHCA & d) DCTB and CardS3 using e) CHCA & f) DCTB as matrix. ........................................................... 70

Figure II - 14. Proposed mechanism for DCTB adduction to an aliphatic primary amine.113....... 71

Figure II - 15. X-Ray diffractograms of pristine MMT and O-MMT.......................................................... 73

Figure II - 16. MALDI-MS spectra, using DCTB-Ag as matrix, of a) CardS1-MMT, b) CardS2-MMT,

and c) CardS3-MMT. ..................................................................................................................................................... 74

Figure II - 17. Chemical structure of furfuryl glycidyl ether (Fge). ......................................................... 75

Figure II - 18. Reaction between epoxy and primary and secondary amine functions. ................. 75

Figure II - 19. MALDI-MS spectra of Fge-grafted a) CardS1-MMT, b) CardS2-MMT, and c)

CardS3-MMT using DCTB-Ag as matrix. ............................................................................................................... 76

Figure II - 20. X-ray diffractograms of CPN prepared with 10 mass% of pristine and

organomodified MMT by CardS1, CardS2 and CardS3. .................................................................................. 78

Figure II - 21. DSC thermograms of BADGE/DAC and CPN prepared with 5, 7, and 10 wt% of

pristine MMT. .................................................................................................................................................................. 80


MMT modified by CardS1. .......................................................................................................................................... 81

Figure II - 23. I) Scanning electron micrographs of the fracture of MMT-CardS3 (above part)

and MMT-CardS1 (bottom part) based CPN. a) corresponds to the topographic micrographs, b)

to the chemical contrast (BSE detector, the lightest the points and the heaviest the elements)

and c) is the aluminium distribution of the analysed area ........................................................................... 82

Figure III - 1. Classical two-step approach for the synthesis of mono-benzoxazine monomers.120

............................................................................................................................................................................................... 86

Figure III - 2. Chemical structure of a) mono-benzoxazine (m-Bz) and b) di-benzoxazine (di-Bz)

monomers. ........................................................................................................................................................................ 86

Figure III - 3. Thermally-induced ring opening polymerization of Bz monomers.120 ...................... 87

16

Figure III - 4. Dimer product of para-substituted m-Bz monomer via ring-opening reaction.12488

Figure III - 5. Possible polymerization reactions sites in order the most to the least

predominant: 1 ortho, 2 para, 3 meta.120 ............................................................................................................. 88

Figure III - 6. Chemical structures of the Bz monomers used for the elaboration of Bz/CNT

nanocomposites.143 – M1: Bisphenol A/aniline based Bz monomer and M2: 1,4-phenylene

diamine/phenol based Bz monomer. .................................................................................................................... 89

Figure III - 7. Representative SEM images of a) pristine kaolin and b) 10 wt% kaolin/EDBz. .... 90

Figure III - 8. Chemical structure and thermal properties of Bz monomers containing carboxylic

groups.158 .......................................................................................................................................................................... 92

Figure III - 9. Chemical structures of Class A and Class B di-Bz monomers. ....................................... 93

Figure III - 10. Chemical structure of Class B di-Bz monomer. ................................................................. 94

Figure III - 11. Synthesis of di-Bz monomers bearing maleimide functional groups. 167 ............... 98

Figure III - 12. Example of naturally occurring phenolic derivatives used for the synthesis of

bio-based Bz monomers. .......................................................................................................................................... 100

Figure III - 13. Schematization of the participation of the aldehyde group in the ring opening

polymerization of the para hydroxyl benzaldehyde Bz monomers.182 ................................................. 103

Figure III - 14. Crosslinking of vanillin-based di-Bz monomers.181 ....................................................... 103

Figure III - 15. Chemical structure of lignin-derivative compounds: coumaric acid (CA), ferulic

acid (FE), and phloretic acid (PA). ........................................................................................................................ 105

Figure III - 16. Available positions for ring opening polymerization of eugenol-based Bz

monomer. ........................................................................................................................................................................ 107

Figure III - 17. Elaboration of crosslinked materials from eugenol-based Bz monomers by

copolymerization between allyl group and bismaleimides.187 ................................................................. 107

Figure III - 18. Chemical structures of a) umbeliferone and b) 4-methylumbeliferone coumarin

compounds. .................................................................................................................................................................... 109

Figure III - 19. Chemical structure of urushiol. ............................................................................................. 113

Figure III - 20. Available positions for ring opening polymerization of urushiol-based Bz

monomer. ........................................................................................................................................................................ 114

Figure III - 21. Synthesis di-Bz asymmetric monomer by reaction between aminophenol and

hydrobenzaldehyde and butylamine (u-butyl-Bz) or hexylamine (u-hexyl-Bz).201 ......................... 116

Figure III - 22. Synthesis of blends of di-eugenol, di-cardanol and asymmetric eugenol/cardanol

di Bz monomers. 202 .................................................................................................................................................... 117

Figure III - 23. Synthesis of symmetric Bz monomers from various phenolic compounds like

phenol, vanillin or cardanol. ................................................................................................................................... 118

Figure III - 24. 1H NMR spectrum (in CDCl3) of di-phenol benzoxazine monomer. ....................... 119

Figure III - 25. 1H NMR spectrum (in CDCl3) of di-vanillin benzoxazine monomer. ...................... 120

17

Figure III - 26. 1H NMR spectrum (in CDCl3) of di-cardanol benzoxazine monomer. .................... 122

Figure III - 27. MALDI-TOF/MS spectrum of di-phenol benzoxazine monomer. ............................ 124

Figure III - 28. HRMS spectrum of di-vanillin benzoxazine monomer. ............................................... 125

Figure III - 29. HRMS analysis of di-vanillin Bz monomer a) Zoom of the experimental product

peaks b) Theoretical mass of the expected product. .................................................................................... 125

Figure III - 30. HRMS spectrum of di-cardanol benzoxazine monomer. ............................................. 126

Figure III - 31. HRMS analysis of di-cardanol Bz monomer a) Zoom of the experimental product


Figure III - 32. MS/MS analysis of di-cardanol Bz monomer. .................................................................. 127

Figure III - 33. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of di-phenol monomer. . 128

Figure III - 34. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of di-vanillin Bz monomer.

............................................................................................................................................................................................. 129

Figure III - 35. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of the di-cardanol

benzoxazine monomer. ............................................................................................................................................. 130

Figure III - 36. Isothermal rheology monitoring of di-phenol Bz monomer at 190 °C – empty

markers: storage modulus G’; filled markers: loss modulus G’’. .............................................................. 131

Figure III - 37. Isothermal rheology monitoring of di-cardanol Bz monomer at 190 °C – empty

markers: storage modulus G’; filled markers: loss modulus G’’. .............................................................. 131

Figure III - 38. Synthesis of the asymmetric Vani-Card Bz monomer from cardanol and vanillin.

............................................................................................................................................................................................. 133

Figure III - 39. 1H NMR spectrum (in CDCl3) of Vani-Card benzoxazine monomer. ....................... 134

Figure III - 40. HRMS analysis of Vani-Card Bz monomer a) Zoom of the experimental product


Figure III - 41. HRMS spectrum of Vani-Card benzoxazine monomer. ................................................ 137

Figure III - 42. DSC thermograms (N2, 20 K/min) of a) di-vanillin, b) Vani-Card Bz monomers

and c) di-cardanol Bz monomer. ........................................................................................................................... 138

Figure III - 43. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of the Vani-Card Bz

monomer. ........................................................................................................................................................................ 139

Figure III - 44. Isothermal rheology monitoring of Vani-Card (circular markers) and di-cardanol

(triangular markers) benzoxazines at 190°C – empty markers: storage modulus G’; filled

markers: loss modulus G’’. ....................................................................................................................................... 140

Figure III - 45. DMA thermograms of poly(di-cardanol), poly(di-phenol) and poly(Vani-Card).

............................................................................................................................................................................................. 142

Figure III - 46. TGA (air atmosphere, 20K/min) thermograms of a) di-cardanol, b) di-phenol

and c) Vani-Card PBz materials. ............................................................................................................................ 143

18

Figure IV - 1. Chemical structure of diglycidyl ether of cardanol (CDGE) – commercially

available NC514 - from Cardolite Corporation................................................................................................ 146

Figure IV - 2. Friedel-Crafts alkylation of phenol with cardanol (ideal reaction pathway). ....... 147

Figure IV - 3. Chemical structure of diglycidyl ether of cardanol determined by 1H NMR

analysis.213 ...................................................................................................................................................................... 148

Figure IV - 4. Chemical structure of CDGE obtained from NMR and SEC analysis.213 .................... 148

Figure IV - 5. Additional chemical compounds composing CDGE determined by MALDI-MS

analysis a) epoxidized cardanol bearing an additional phenol moiety, b) epoxidized cardanol

containing both an epoxidated and a native phenol on its side chain, c) epoxidized cardanol

linked to a native cardanol, d) two epoxidized cardanol linked by a native phenol.204 ................. 149

Figure IV - 6. CDGE cross-linking agents a) isophorone diamine and b) Jeffamine D400. .......... 150

Figure IV - 7. Chemical structure of 1,2-diaminocyclohexane (DAC) cross-linking agent. .......... 151

Figure IV - 8. Synthesis of Pbz/epoxy co-networks.217 ............................................................................... 152

Figure IV - 9. Reaction between epoxy and primary and secondary amine functions. ................. 153

Figure IV - 10. Reaction scheme of opening the oxazine ring via an amine nucleophilic attack.229

............................................................................................................................................................................................. 154

Figure IV - 11. Sequential synthesis of IPN. .................................................................................................... 155

Figure IV - 12. In-situ IPN synthesis. .................................................................................................................. 155

Figure IV - 13. Nucleation and growth mechanism. .................................................................................... 156

Figure IV - 14. Gyroïdal structure. ...................................................................................................................... 156

Figure IV - 15. a) Expected reactions during the IPN sequential in-situ synthesis, b) in-situ

sequential synthesis of a poly(CDGE)/poly(Bz) IPN material. ................................................................. 158

Figure IV - 16. Chemical structure of the EDBz model Bz monomer. ................................................... 159

Figure IV - 17. Curing conditions of CDGE with various diamine compounds monitored by DSC

analysis (N2, 20 K/min), compared to the curing conditions of the EDBz monomer (Dashed

curve, (N2, 20 K/min)). .............................................................................................................................................. 160

Figure IV - 18. Curing conditions of various systems a) CDGE with IPD, b) EDBz and c) 60/40

CDGE/EDBz with IPD monitored by DSC analysis (N2, 20 K/min). ........................................................ 162

Figure IV - 19. Curing conditions of CDGE/EDBz (60/40 % wt) systems. ......................................... 163

Figure IV - 20. DSC analysis (N2, 20 K/min) of the poly(CDGE) material (without EDBz) after the

first curing step of 16 h at 100 °C. ........................................................................................................................ 164

Figure IV - 21. DSC analysis (N2, 20 K/min) of the poly(CDGE)/EDBz (60/40) system after the

first curing step of 16 h at 100 °C, and compared to neat poly(CDGE) after 16 h at 100 °C. ....... 165

Figure IV - 22. DSC analysis (N2, 20 K/min) of the poly(CDGE)/poly(EDBz) (60/40) material

after the full curing program (1 h at 160 °C, 2h at 180 °C, 2h at 200 °C and 30 min at 220 °C). 166

19

Figure IV - 23. Evolution of the storage modulus E’ of poly(CDGE)/poly(EDBz) IPNs (80/20,

70/30, 60/40, 50/50, 40/60, 30/70 and 20/80) as a function of temperature, obtained by DMA

(Tension mode with 0.05 % strain, 1 Hz and 3 °C/min). ............................................................................ 167

Figure IV - 24. Evolution of the storage modulus E’ and tanδ of poly(CDGE)/poly(EDBz) IPNs

(80/20, 70/30 and 60/40) as a function of temperature, obtained by DMA (tension mode with

0.05% strain, 1Hz and 3°C/min). .......................................................................................................................... 168

Figure IV - 25. Evolution of the tanδ of poly(CDGE)/poly(EDBz) IPNs (50/50, 40/60, 30/70 and

20/80) as a function of temperature, obtained by DMA (tension mode with 0.05% strain, 1Hz

and 3°C/min). ................................................................................................................................................................ 169

Figure IV - 26. Shear modulus of poly(CDGE)/poly(EDBz) IPN materials versus EDBz volume

fraction compared with modulus-composition models. ............................................................................. 172

Figure IV - 27. DSC thermograms of poly(CDGE)/poly(EDBz) IPNs (80/20, 70/30, 60/40,

50/50, 40/60, 30/70 and 20/80) and poly(CDGE) and poly(EDBz), during the heating of

swollen materials (N2, 5 K/min). .......................................................................................................................... 173

20

List of Tables

Table I - 1. Composition of the phenolic components in natural and technical CNSL.11 ................. 27

Table I - 2. Composition of the abundances of the constituents of cardanol by various

techniques.10 .................................................................................................................................................................... 28

Table I - 3. Percentage retention of the physical properties after ageing of the PVC compounds

dioctyl phthalate (DOP), Cl-cardanol, Cl-cardanol acetate, Cl-cardanol methyl ether.39 ................. 31

Table I - 4. Physico-chemical properties of the reactive surfactants compared to the properties

of standard non-reactive sodium dodecyl sulfonate anionic surfactant. ............................................... 35

Table I - 5. Isolated product yields (%) of phase transfer catalysed reactions.49 .............................. 36

Table I - 6. Properties of phenalkamines synthetized from cardanol, formaldehyde and

isophorone diamine.56 ................................................................................................................................................. 39

Table I - 7. DTA measurements describing antioxidants effects of various antioxidants in MLO

under air atmosphere.59 (Ti: initial thermal degradation temperature, Tmax: degradation

temperature.) .................................................................................................................................................................. 41



temperature.) .................................................................................................................................................................. 42

Table I - 9. Inhibition rate constants (kinh) obtained by studying the AIBN initiated autoxidation

of styrene at 30 °C in homogeneous solution using chlorobenzene (PhCl) as a solvent, or in a

two-phases water/styrene system.62 .................................................................................................................... 42

Table I - 10. Thermal of CAP1 and CAP2 based PU materials.77 (T10% is the temperature at 10

wt% weight loss and Tmax is the temperature at maximum rate weight loss). .................................... 48

Table II - 1. Example of fillers for the elaboration of nanocomposites.83 ............................................. 54

Table II - 2. CardS1 experimental and theoretical integrations. ............................................................... 66



Table III - 1. Polymerization temperatures of (cardanol/aniline) PBz cured with 1 mol%

catalyst.156 ......................................................................................................................................................................... 91

Table III - 2. Thermal properties Bz materials from reaction between m1 and carboxylic-

containing Bz co-monomers m2, m3, and m4. 158 ............................................................................................ 93

Table III - 3. Reaction times of synthesis of Bz monomers in CHCl3 at reflux with increasing

diamine chain length.162 .............................................................................................................................................. 95

21

Table III - 4. Melting point (Tm) and polymerization temperature (Tp) of model aromatic-di-Bz

monomers and Tg of their corresponding aromatic-PBz materials. ......................................................... 96

Table III - 5. Thermal properties of aliphatic- di-Bz monomers, synthetized from various chain

length linear diamines and phenol, and Tg of their corresponding aliphatic-PBz materials. ........ 97

Table III - 6. Thermal properties of vanillin-based Bz monomers, synthetized from mono-

functional amines or diamines, and Tg and T5% of their corresponding PBz materials. ................. 102

Table III - 7. Thermal properties of guaïacol-based Bz monomers, synthetized from mono-


Table III - 8. Thermal properties of lignin-derivative-based Bz monomers, synthetized from

mono-functional amines or diamines, and Tg and T5% of their corresponding PBz materials. ... 106

Table III - 9. Thermal properties of eugenol-based Bz monomers, synthetized from mono-


Table III - 10. Thermal properties of coumarin-based Bz monomers, synthetized from mono-


Table III - 11. Thermal properties of cardanol-based Bz monomers, synthetized from mono-


Table III - 12. Thermal properties of urushiol-based Bz monomers, synthetized from amines or

diamines, and Tg and T5% of their corresponding PBz materials. ............................................................ 114

Table III - 13. Assignments of the 1H NMR peaks of the di-phenol benzoxazine monomer and

their theoretical and experimental integrations. ........................................................................................... 120

Table III - 14. Assignments of the 1H NMR peaks of the di-vanillin benzoxazine monomer and


Table III - 15. Assignments of the 1H NMR peaks of the di-cardanol benzoxazine monomer and


Table III - 16. Assignments of the 1H NMR peaks of the asymmetric Vani-Card Bz monomer and


Table III - 17. Thermal properties of symmetric and asymmetric di-benzoxazine monomers.

Values are obtained from DSC (a), TGA (b) and rheology (c) analyses. ................................................ 140

Table III - 18. Thermal properties of symmetric and asymmetric PBz materials. Values are

obtained from DMA (a), and TGA (b) analyses. ............................................................................................... 143

Table IV - 1. Thermomechanical properties of CDGE cured with IPD or Jeff400, compared to

BADGE/IPD network.213 ............................................................................................................................................ 150

22

General Introduction and Context

In the recent years, the interest of the researchers, both from the academy and industry, in the

chemistry of renewable resources and related materials has considerably grown. Indeed, until

recently, the largest part of the resources used for the production of commodity materials is

mainly petroleum-based compounds. Furthermore, the world production of plastic materials is

constantly increasing, reaching in 2014 a production of 311 million tons of plastic, using 8 % of

the global petroleum annual world production.1 The production of petroleum-based plastic

materials concerns a wide range of applications such as packaging (39.5 %), building and

construction (20.1 %), automotive (8.6 %), electrical and electronics (5.7 %) or agriculture (3-4

%). Various sectors such as consumer and household appliances, furnitures, sports, or health and

safety constitute 22.7 % of the global demand. However, the depletion of fossil resources,

combined to their increasing prices and the growing environmental concerns, led to huge demand

in the development of new bio-based precursors. Nowadays, bioplastics are representing a

minority of the world plastic production, less than 1 % of the global plastic production.2 In 2013

the bioplastic production amounted only around 1.6 million tons. Nevertheless, the demand is

rising, and by 2018 the production capacity is expected to increase to 6.7 million tons, leading to

more and more sophisticated bioplastic materials (Figure 1).

Figure 1. Global production capacities of bioplastics (In 2013 and forecast for 2018).2

23

In consequence, numerous researchers focused in the past few years on the use of naturally

occurring building-blocks for the synthesis of monomers and polymeric materials. Up to now, the

natural resources used to this aim are predominantly agricultural crops such as corn, cereals,

sugar beets and sugar cane (first generation feedstock); most of them competing with food value

chain. Nevertheless, the bioplastic industry favours now the natural resources provenance rather

towards non-food crops and non-edible by products (second and third generation feedstock),

among others, cellulose. Indeed, a large amount of cellulosic by-products are produced by the

growing of crops such as straw, corn stover or bagasse which could be recovered. Other

renewable materials such as wood, proteins, lignin, tannins, starch, vegetables oils or even animal

resources such as chitin, are also widely studied and used. However, many of these naturally

occurring resources exhibit important drawbacks such as low purity and high molar masses,

reducing their industrial development. The depolymerisation of lignin for example also remains

very challenging, limiting its exploitation as source of chemical building blocks.3 Among the

possible raw renewable materials available for the development of new bio-based materials,

cardanol is gaining considerable interest as a natural source of phenol and a versatile building

block.4 Cardanol is produced from Cashew Nutshell Liquid (CNSL), and is an economical and

abundant non-edible agricultural annually renewable resource used in many applications in

research and industry.5 Indeed, in 2013, the world production of cashew nuts in shell was

estimated to 4.4 million tons.6 Beside the sustainability, availlabatility and the advantageous price

of raw cardanol compound, its particular aromatic structure makes it an interesting and

promising natural alternative to petrochemical derived phenols. Indeed, due to similar reactivity

to a phenol compound and through various chemical modifications on its three main availlable

reactive sites, a wide range of molecules can be designed with wide application range such as

surfactants, plasticizers or polymer precursors. The raw cardanol compound was already

intesively studied, and a state of the art of the possible chemical modifications and their

applications will be described in a first introductive chapter. The following chapters are them

highlighting various chemical modification strategies we applied to cardanol for the elaboration,

or the reinforcement of polymeric materials as tentative ways to find new high value applications

of these raw biobased building blocks.

First of all, we report in Chapter II the synthesis of a set of novel cationic surfactants prepared

from cardanol. The synthetized ammonium cardanol-based surfactants exhibited interesting

properties. They were thus herein applied for the organomodification of Montmorillonite (MMT),

a clay mineral widely used as filler in polymer materials for its reinforcing, thermal and gas

barrier properties. Indeed, it is well established that the chemical structure of surfactants used

for the organomodification of clay minerals plays an important role on the clay exfoliation during

24

the elaboration of nanocomposite materials. The compatibilization of clay mineral and polymer

material may be enhanced by the incorporation of reactive surfactants capable to covalently graft

to monomers and polymer chains. It will be evidenced that cardanol-based surfactants act as

efficient compatibilizers of MMT within epoxy polymer. Furthermore, it will be demonstrated that

the reactivity of the synthetized surfactants plays a particular role on the clay exfoliation

mechanism within an epoxy matrix. Interestingly, different (nano)composite structures were

observed depending on the reactivity of the surfactants.

As highlighted before, cardanol is a naturally occurring phenolic compound that has recently

attracted attention for the synthesis of benzoxazine monomers. Undergoing the efforts to

promote the development of bio-based benzoxazine thermosets, we explore in Chapter III a new

strategy for the elaboration of bio-based and processable Bz-materials. In particular, Bz

monomers from cardanol alone or in conjunction with some lignin derivatives – like vanillin –

were studied. A versatile synthesis of asymmetric di-benzoxazine monomers from naturally

occurring phenolic compounds cardanol and vanillin was developed. By taking advantage of the

low reactivity of cardanol, a mono-substituted cardanol-based benzoxazine monomer was

prepared and further coupled with vanillin to yield vanillin-cardanol di-benzoxazines. The

asymmetric monomer presents the great advantage of displaying a low melting temperature and

thus a wide processing window, facilitating its processing (melting and shaping). Furthermore, a

moderate gelation time was observed as well as high Tg for the polymerized material. Such

strategy constitutes an efficient and versatile route for an easy elaboration of bio-based

monocomponent thermosets.

Finally, in the last chapter we envision the substitution of Bisphenol A - a well-known endocrine

disruptor - in coatings, by using diglycidyl ether of cardanol (CDGE). Because of its weak

properties (Tg, storage modulus, water repellence), coatings prepared with CDGE need to be

reinforced. In particular, we focused on a macromolecular reinforcement by the elaboration of

interpenetrating polymer networks of CDGE and polybenzoxazine (PBz). Indeed, CDGE thermoset

materials display poor thermo-mechanical properties, whereas PBz resins are well-known for

being high performance materials. In spite of the possible co-crosslinking between cardanol

diglycidyl ether and benzoxazine monomers, leading to polymer co-networks, we found the

appropriated experimental conditions to only tangle the two polymer networks without chemical

links between the two networks. The elaboration and the properties of these interpenetrating

polymer networks are reported in this last chapter.

25

Chapter I: Introduction

1 Cashew nutshell liquid: extraction and composition

The cashew nut industry is largely present in countries of tropical regions, such as India, Brazil,

and Viet Nam. The global world production of cashew nut crops was estimated around 4 million

tons in 2012 (Food and Agriculture Organisation (FAO)), mainly located in Vietnam (1.2000.00

tonnes/year) followed by Nigeria, India, etc. (Figure I - 1 (FAO STAT data, 2013)).6

Figure I - 1. Main cashew nut producing countries in 2012.

The cashew nut stems from the cashew apple fruit (Figure I – 2) of the cashew tree Anacardium

occidentale L., native species from Brazil. The cashew nut is the seed of the cashew apple. Both

cashew apple and nut are comestible and widely consumed products.

Figure I - 2. Representation of cashew apples.

Cashew nuts are commercialised without their shell due to a highly vesicant substance it contains

at a raw state: the cashew nutshell liquid (CNSL) is considered as an important by-product of this

industry.

26

Extracted from the soft honeycomb structure of cashew nutshells - mesocarp spongy - (Figure I

-3) during the shelling process of cashew nuts, CNSL is an economical and abundant non-edible

agricultural renewable resource used in many applications in research and industry. CNSL

constitutes about 20-25% of the weight of the cashew nut. It is usually used in its technical state

in various industrial applications such as brake linings, surface coatings, paints, varnishes,

lacquers, adhesives or laminates.5

Figure I - 3. Cross section of a cashew nut and nutshell.

CNSL is the most known source of phenolic lipids in plants. The oil is mainly composed of four

phenolic constituents – hydroxyalk(en)ylbenzene homologs namely anacardic acid, cardanol,

cardol and 2-methyl cardol - substituted in meta position by an unsaturated C15 alkyl chain

(Figure I - 4). Unlikely to other phenolic lipids found for instance in cereals, the chain length of

these constituents is not varying. However, each of them is composed of a mixture of four

components differing by their unsaturation degree, from saturated to tetraenoic one.7

Figure I - 4. Chemical structure of CNSL components a) anacardic acid, b) cardanol, c) cardol

and d) 2-methylcardol.

Different oil compositions, i.e. the abundance of the four constituents and their respective

unsaturated forms, are obtained depending on the extraction process. These processes can be

roughly classified in two types: extractions in cold/room temperature conditions and extractions

in heating conditions.

27

Naturally occurring CNSL - obtained by cold-pressing or solvent-extraction –contains mainly four

phenolic constituents: anacardic acid (70-80%), cardol (15-20%), cardanol (1-7%) and traces of

2-methyl cardol (1-4%).

Technical CNSL (i.e. commercial CNSL) is extracted by roasting the nutshells and is mainly

constituted of cardanol (60-85%), cardol (4-20%), and traces of 2-methylcardol (1-5%). It barely

contains anacardic acid which is converted into cardanol through thermal decarboxylation during

the roasting and refining processes (Figure I - 5). Oligomeric or polymeric materials (7-20%)

were also found to be present mainly in technical CNSL.8,9

Figure I - 5. Anacardic acid decarboxylation.

The composition of the different grades of the obtained oils by these extraction processes are

gathered in Table I - 1.10

CNSL type CNSL phenolic components (%)

Anacardic acid (%) Cardanol (%) Cardol (%) 2-methylcardol (%)

Natural CNSL 74.1-77.4 1.2-9.2 15.0-20.1 1.7-2.6

Technical CNSL 1.0-1.8 74.7-84.7 11.6-18.9 2.2-5.2

Table I - 1. Composition of the phenolic components in natural and technical CNSL.11

2 Extraction of cardanol from CNSL and reactivity

The industrial grade of cardanol oil recovered from CNSL, may reach 90% of cardanol content

and a smaller percentage of cardol and methylcardol.12, 13 As above mentioned, cardanol is a

mixture of four phenolic molecules differing by their degree of unsaturation of their alkyl side

chain and the determination of their relative abundance has been the subject of many researches

through various methods. Table I - 2 summarizes the abundances of the different unsaturations

as a function of the employed characterization technique. It can be observed that depending on

the characterization technique and on the origin of the product the unsaturation abundances can

slightly vary.

28

Cardanol side chain

unsaturations (%)

Saturated

(%)

Monoene (%) Diene (%) Triene (%)

Employed technique

Molecular distillation - 60.0 10.0 30.6

Silver ion chromatography 5.4 48.5 16.8 29.3

TLC-GLC 2.7 29.5 16.6 51.2

TLC-mass spectroscopy 2.0 31.3 15.2 51.5

Table I - 2. Composition of the abundances of the constituents of cardanol by various

techniques.10

Cardanol was thus found to display an average of 1.5 unsaturations, with a majority of tri-

unsaturated compound (40-50%), followed by the mono-unsaturated compound (30-35%), the

di-unsaturated compound (15-20%), and very few saturated compound (1-4%) (Figure I – 6).

Figure I - 6. Average compositions of the cardanol alkyl side chain.

Cardanol displays a similar reactivity than phenol, and is thus a promising renewable substituent

to petroleum-based phenolic compounds. Indeed, cardanol has three different sites available for

panoply of chemical reactions (Figure I – 7).

Figure I - 7. Representation of the possible chemical modifications on the three reactive sites of

cardanol.

29

The reactive hydroxyl group on cardanol allows chemical reactions such as esterification,14

allylation,15, 16 epoxidation,17-25 or ethoxylation.26, 27 Structural changes may also occurred by

reacting the aromatic ring, for example through condensation,28 nitration,29 sulfonation,30,31

bromination,32 and hydrogenation.33 Furthermore, cardanol can also undergo chemical

modifications on the C15 alkyl side chain. Indeed, the side chain unsaturations enable reactions

such as hydrogenation,33 hydrosilylation,34 epoxidation,17, 18 phenolation,35 or metathesis

reactions.36

Consequently, cardanol is used in a wide range of applications (plasticizers, surfactants, curing

agents, antioxidants), depending on its chemical modification, as described in the following sub-

chapter. In the study described in the Chapter II, we took advantage of the amphiphilic chemical

structure of cardanol to synthetize ammonium surfactant by reaction on the phenolic hydroxyl

function (Figure I – 8a). The synthesis of cardanol-based benzoxazine monomers highlighted in

Chapter III occurred also by reaction on the cardanol hydroxyl group, coupled to a reaction on the

aromatic ring on cardanol (Figure I – 8b). Finally the synthesis of a cardanol diglycidyl ether

compound studied in the Chapter IV resulted from modification on both hydroxyl phenolic group

and alkyl side chain unsaturations of cardanol (Figure I – 8c).

Figure I - 8. Fine chemicals and functional molecules from cardanol.

30

3 Cardanol based chemicals and functional molecules

Among fine chemicals and functional molecules from cardanol reported in the literature, there

are plasticizers, surfactants, curing agents or antioxidants.

3.1 Plasticizers and reactive diluents

The incorporation of a plasticizer molecule within a polymeric material increases its flexibility

and processability. A plasticizing compound is usually a low molecular weight molecule with both

suitable polar and non-polar entities. Indeed a plasticizer molecule is able to penetrate within a

polymeric matrix through hydrophobic compatibility and to establish polar attractive forces with

the polymeric matrix chains reducing thus the cohesive forces between the polymer chains

(Figure I – 9).

Figure I - 9. Schematic representation of polymer matrix a) plasticizer-free and b) in presence

of a plasticizer.

Due to its chemical and physical properties, cardanol is a promising bio-based plasticizer. The

C15 alkyl chain represents the hydrophobic entity of cardanol, while the hydroxyl group can be

chemically modified into a hydrophilic group endowing plasticizing properties to the molecule.

Hence, with the actual concern of replacing the commonly used phthalate-based plasticizers

because of toxic release,37 both raw and chemically modified cardanol compounds are intensively

used as plasticizer.

For instance neat cardanol has been used as plasticizer for Poly(methyl methacrylate) (PMMA)

as reported by Prabhakaran et al.38. The rheological properties were influenced by the addition

of cardanol to PMMA. The viscosity decreased from 6.4 Pa.s to 1.5 Pa.s with increasing the weight

31

ratio of cardanol/PMMA from 0.33 to 1. Furthermore, the plasticizing effect of cardanol was

evidenced by the decrease of the Tg of PMMA-cardanol blends from 48 °C to -12 °C with the

addition of 50 wt % of cardanol in PMMA.

Chlorinated cardanol as well as its chlorinated acetyl and methoxy derivatives were tested for the

partial replacement of dioctyl phthalate (DOP) in polyvinyl chloride (PVC) leading to an

improvement of the properties of the material as resumed in Table I – 3.39 The DOP was added

to the PVC compound in a 50/50 ratio to the synthetized cardanol-based plasticizers.

Plasticizer

DOP

DOP/Cl-

cardanol

DOP/Cl-

cardanol

acetate

DOP/Cl-

cardanol methyl

ether

Percentage

retention

Physical

properties

(%)

Hardness 105.4 108.1 109.0 94.36

Tensile

strength

122.8 100.6 101.2 114.8

Modulus 143.4 111.7 126.2 138.2

Elongation 90.9 83.3 92.9 92.3

Table I - 3. Percentage retention of the physical properties after ageing of the PVC compounds

dioctyl phthalate (DOP), Cl-cardanol, Cl-cardanol acetate, Cl-cardanol methyl ether.39

The chlorinated cardanol methyl ether (Cl-cardanol methyl ether) appears to be a good plasticizer

for PVC with comparable performances to DOP, particularly thermal once. Similarly, acetyl

cardanol derivatives were evaluated as plasticizer in PVC.14, 40, 41 Thermal and mechanical

properties of the resulting PVC-based materials were comparable to those of PVC plasticized with

di-ethyl-hexyl-phtalate (DEHP) or DOP lonely.

However, a well-known drawback of plasticizers is their migration from the bulk to the surface

of the host polymer matrix. To prevent this phenomenon plasticizers are generally modified with

a reactive function towards the polymer matrix (reactive plasticizer). Furthermore, the addition

of a reactive plasticizer to high viscosity epoxy is known to reduce the viscosity and facilitate the

materials processing. In the case of cardanol, the most common reactive cardanol-based

plasticizer used to prevent its migration is obtained from the reaction of cardanol with

epichloridrin in basic conditions. This cardanol derivative is commercially available under the

Trade mark NC-513 (Cardolite) (Figure I - 10).42

32

Figure I - 10. Chemical structure of mono-epoxidized cardanol NC-513 from Cardolite.

Cardolite finds applications in solvent free epoxy systems used in protective, industrial, and floor

coatings. The reactivity of this mono-epoxy cardanol has been enhanced by the epoxidation of its

side chain unsaturation to form cardanol poly-epoxy derivative (Figure I - 11). This compound

was then used as reactive diluent for a cardanol-based epoxy.18 The viscosity of a cardanol-based

epoxy decreased significantly from 4780 mPa.s to 2150 mPa.s with the addition of cardanol poly-

epoxy derivative from 10 to 20 %.

Figure I - 11. Chemical structures of cardanol polyepoxy derivatives plasticizers.18

3.2 Surfactants

Surfactants are amphiphilic molecules constituted of a hydrophobic part (the tail) and a

hydrophilic group (the head). They are largely used as detergents, wetting and/or foaming

agents, emulsifiers or dispersants due to their ability to lower the surface tension of a liquid,

between two liquids or between a liquid and a solid.43 Surfactants are classified into four classes

based on the nature of the hydrophilic group (Figure I -12).

Petroleum-stemmed linear alkyl benzenes are the most commonly used reactants for the

synthesis of surfactants. A sustainable alternative would be the synthesis of cardanol-based

surfactants as it could be expected from its appropriate chemical structure. Even though

unmodified cardanol cannot be considered as surfactant but its chemical structure and inherent

amphiphilic properties are ideal for the synthesis of bio-based surfactants. Indeed the C15 alkyl

chain represents the hydrophobic part while the aromatic ring bearing a hydroxyl group

represents the slightly hydrophilic part. The amphiphilic properties of cardanol can be

accentuated by chemical modifications of the phenolic hydroxyl group, obtaining thus cardanol-

33

based surfactants. Through numerous possible chemical modifications of its phenolic hydroxyl

function, various types of surfactants were synthetized from cardanol such as anionic, non-ionic

or cationic surfactants.

Figure I - 12. Schematic representation of the various types of surfactants a) cationic, b)

anionic, c) non-ionic and d) zwitterionic.

3.2.1 Anionic surfactants

Anionic surfactants are negatively charged and have a pronounced hydrophilic character. They

are usually used as wetting or foaming agents in the diverse industries. Anionic surfactants are

the most developed type of cardanol-based surfactants. Cardanol-based sulfonate surfactants are

synthetized from different synthesis pathways. Cardanol sulfonation can be achieved for example

by reaction with fuming sulphuric acid (Figure I -13).30, 31 Sulfonate cardanol surfactant (SC) was

found to have comparable detergent properties to traditional dodecylbenzene sulfonate (DDBS)

surfactant, and can thus be considered as a good alternative. Indeed, the values obtained for

cardanol sulfonate surfactants were very close to those for commercial DDBS when comparing

surface tensions (obtained minimum surface tension = 28 mN/m and 32.25 mN/m for SC (15 %

w/v) and DDBS (15 % w/v) surfactants respectively) and critical micelle concentrations (CMC =

0.372 mol/L and 0.435 mol/L for SC and DDBS surfactants respectively).

34

Figure I - 13. Synthesis of cardanol sulfonate surfactants.30

A sulfonated cardanol-based surfactant was synthetized through diazotation coupling reaction

between cardanol and sulfonic acid diazonium salt (Figure I - 14).44 This surfactant generates

stable emulsions of aniline in water. The corresponding polymer, polyaniline (PANI), is a versatile

conducting polymer in oxidized state (component of organic light emitting devices or organic

photovoltaic devices). As PANI is positively charged it requires counter ion, called dopant, to

ensure electroneutrality. The molecular structure of this cardanol-based dopant allows the

preparation of conducting highly ordered and water soluble PANI nanofibers. Moreover, the

cardanol-based dopant displays free hydroxyl phenolic functionalities, allowing the possibility to

fine-tune the PANI material.

Figure I - 14. Synthesis of cardanol diazonium sulfonate surfactant.44

Anionic type carboxylate surfactants can also be synthetized by modification of the phenolic

hydroxyl function of cardanol (Figure I - 15).45 They were shown to lower the surface tension

and to produce microemulsions in mixture with sodium dodecyl sulfate. A CMC of 8.3x10-4 mol/L

with a corresponding surface tension of 29.16 mN/m was reported.

Figure I - 15. Chemical structure of cardanol carbonate surfactant.45

Surfactants may also bear reactive functions and could thus be able to take part in polymerization

reactions. These reactive-surfactants known as “surfmers” can be used in order to improve the

final material properties.46 Sulfonated acrylate cardanol surfmers (Figure I - 16) are obtained by

35

reaction between different cardanol acrylates and chlorosulfonic acid, and their properties were

compared with standard non-reactive sodium dodecyl sulfonate anionic surfactants (SDS) (Table

I - 4).47

Figure I - 16. Chemical structure of sulfonated acrylate cardanol surfactants a) sulfonated-3-

pentadecyl phenyl acrylate and b) sodium-2-acryloxy ethan-1-oxy(3-pentedecyl) benzene

sulfonate.47

The CMC of the reactive surfactants were reported to be much lower than the conventional SDS

surfactant. Nevertheless, no evaluation of the influence of the reactive surfactants on materials

elaboration were reported by Kattimuttathu et al..47

Compound CMC (mol/L) Surface tension at CMC

(mN/m)

sulfonated-3-pentadecyl

phenyl acrylate

8.7 x 10-5 35.52

sodium-2-acryloxy ethan-

1-oxy(3-pentedecyl)

benzene sulfonate

1.7 x 10-5 31.61

sodium dodecyl sulfonate 0.37 32.25

Table I - 4. Physico-chemical properties of the reactive surfactants compared to the properties

of standard non-reactive sodium dodecyl sulfonate anionic surfactant.

3.2.2 Non-ionic surfactants

Non-ionic surfactants may also be synthetized from cardanol, especially polyethoxylates (Figure

I - 17) that are commonly based on fatty alcohols or alkylphenols.27, 48 Their properties were

characterized by measuring their reduction in surface tension of water by dilute solutions (1 %)

of polyethoxylates, and determine the optimum ethoxylate chain length. It was found that

cardanol polyethoxylate with a C8 ethoxylate chain length showed similar surfactant properties

than traditional t-nonylphenol polyethoxylate.

36

Figure I - 17. Chemical structure of cardanol polyethoxylate surfactants.27, 48

3.2.3 Cationic surfactants

Cationic surfactants can also be synthetized from cardanol. Nevertheless only two studies are

reported in the literature. The synthesis of a quaternary ammonium salt from cardanol was

described.49 The distinctive feature of this compound is the quaternary ammonium located at the

end of the aliphatic chain of cardanol aiming at enhancing the lipophilic character of the

surfactant (Figure I - 18).

Figure I - 18. Chemical structure of cardanol quaternary ammonium salt surfactants.49

Several heterogeneous reactions such as oxidations and Williamson ether synthesis were tested

with cardanol quaternary ammonium salt as phase transfer catalyst. The synthesis yields were

reported similar or even higher to those obtained with a commercially available quaternary

ammonium salt (Aliquat®) (Table I - 5).

Yields (%) of phase transfer catalysed reactions

quaternary

ammonium salt

KMnO4 oxydation NaClO oxydation Williamson ether

synthesis

cardanol based

R = CH3

76 67 76

cardanol based

R = CH2CH3

74 27 98

cardanol based

R = CH2CH2CH3

60 26 84

Aliquat® 64 49 60

Table I - 5. Isolated product yields (%) of phase transfer catalysed reactions.49

37

It is worthy to note that such ammonium salts can find applications for the functionalization of

fillers, like mineral clays. Verge et al.50 reported the synthesis of an ammonium surfactant from

cardanol for the compatibilization and dispersion of sepiolite clay into epoxy thermoset. Mono-

epoxidized cardanol – commercially available NC-513 – was reacted with ethylene diamine and

protonated in acid medium (Figure I - 19). Cardanol-based ammonium surfactants were found

to enhance the compatibility between sepiolite clay and epoxy networks. The studies dealing with

these cationic cardanol-based surfactants are developed in Chap III.

Figure I - 19. Synthesis of cardanol ammonium salt surfactants.51

3.3 Curing agents

With the trend to decrease the carbon footprint of plastics, bio-based curing agents were found

to be particularly appropriate for the preparation of epoxy-based thermosets. More particularly,

phenalkamine is the most commonly developed curing agent from cardanol.52 Phenalkamines are

synthetized by Mannich reaction between cardanol, formaldehyde and diamines (Figure I - 20).

Figure I - 20. Synthesis of cardanol phenalkamine curing agent.52

They advantageously allow the curing of epoxy resin at low temperature (T = 25 °C)53, 54 and lead

to the improvement of the toughness of the resulting resins thanks to the flexible alkyl chain.

Phenalkamines synthetized by reacting cardanol with a mixture of hexamethylenediamine (HDA)

and diethylenetriamine (DETA) (Figure I - 21) were shown to significantly improve the

toughness of Bisphenol A diglycidyl ether (BADGE) epoxy resins in comparison to DETA as curing

agent.55 Additionally a clear decrease of the Tg was observed. Indeed the Tg of the BADGE epoxy

material cured with a phenalkamine synthetized from cardanol and HDA (Tg = 49.5 °C) was found

to be significantly lower than the Tg of a BADGE epoxy material cured with DETA (Tg = 126.7 °C).

38

Figure I - 21. Chemical structure of phenalkamine component from a) hexamethylenediamine

and b) diethylenetriamine.55

The final properties of thermosets cured with phenalkamine compounds depend on the kind of

polyamine used for the synthesis (aromatic or aliphatic) and on the molecular weight of the

resulting phenalkamine, as well as on the amine percentage. The molecular weight of the

resultant phenalkamine depends on the ratio of cardanol, amine and formaldehyde used.

Kathalewar et al. studied the effect of the molecular weight of phenalkamines on the curing and

on the properties of epoxy coatings.56 Phenalkamines of different molecular weight and amine

content – polyphenalkamines - were synthetized from the reaction between cardanol,

formaldehyde and varying concentrations of isophorone diamine (IPD) (Figure I - 22).

Figure I - 22. Synthesis of phenalkamine compounds from cardanol with varying molecular

weight and amine content.56

BADGE epoxy based coatings were then elaborated by curing with the various phenalkamines

and compared with BADGE coatings cured with commercial phenalkamine ARK351. All the

thermosets exhibited single Tg values (Table I – 6).

The Tg values obtained using DSC increased in the order ARK351 < PA1 < PA2 < PA3. An

increasing of the crosslinking density and of the Tg of the thermosets was reported to be in

39

relation with the increase of the phenalkamine molecular weight and amine content. In addition,

it is assumed that the cycloaliphatic moiety in cardanol-based phenalkamines samples was also

responsible for higher Tg than ARK351 sample, which was based on aliphatic polyamine.

Properties PA1 PA2 PA3 ARK351

Mn (g/mol) 498 843 1371 458

Tg (°C) 71 75 88 65

Cross-link

density

(mol/m3)

107 373 784 659

Table I - 6. Properties of phenalkamines synthetized from cardanol, formaldehyde and

isophorone diamine.56

Nevertheless, the high toxicity of formaldehyde, identified as a carcinogenic compound, in

addition to low primary amine functionality of the resulting phenalkamines are main drawbacks

for the use of Mannich-based phenalkamine curing agents. To overcome these shortcomings

Darroman et al.16 proposed the synthesis of a cardanol-based aromatic amine (cardanol

cysteamine) by thiol-ene chemistry (Figure I - 23) and the elaboration of a fully bio-based epoxy

thermoset material.

Figure I - 23. Synthesis of cardanol-based phenalkamine compound by thiol-ene chemistry.16

The researchers focused on synthesizing a poly-amine cross-linking agent. Cardanol was first

allylated by reaction with allyl bromide and the unsaturation of the cardanol alkyl side chain

could be functionalized by thiol-ene chemistry by reaction with hydrochloride cysteamine.

Thermosets materials from cardanol-based diglycidyl ether compound (NC-514), cured with

commercial NX-5454 phenalkamine and with cardanol cysteamine, respectively (Figure I - 24)

were elaborated and their thermo-mechanical properties were compared.

The glass transition temperature values are low for both formulations NC-514/NX-5454 (1/1

ratio) and NC-514/cardanol cysteamine (1/1 ratio) with Tg = 38 °C and 21 °C respectively. The

crosslinking densities of the corresponding networks were also calculated from the DMA storage

modulus at 60 °C above the Tg. The crosslinking density of the NC-514/NX-5454 (ʋe = 280.0

40

mol/m3) is significantly higher than for the NC-514/cardanol cysteamine network (ʋe = 20.3

mol/m3). The higher Tg and crosslinking densities of NC-514/ NX-5454 network can be explained

by the short diethylene triamine (DETA) used for the synthesis of NX-5454 phenalkamine.

Figure I - 24. Chemical structures of a) cardanol-cysteamine, and b) commercial NX-5454

phenalkamine.

3.4 Antioxidant

Antioxidants are used as additives in various polymer-based materials. Indeed, their presence

inhibits the deterioration of the organic material by oxidation under atmospheric conditions

which increases the material lifetime. The most current and efficient additives are ortho and/or

para substituted phenolic compounds. The anti-oxidant effect is depending on the substituents

electronic effects and on their steric hindrance. Indeed, electron-donating effect of the

substituents increases the hydroxyl oxygen electron density, resulting in an efficient radical trap.

An important steric hindrance of the substituents prevents the coupling of phenoxy radicals and

increases their efficiency.57

Figure I - 25. Chemical structures of cardanol-based antioxidants.

41

Cardanol, through its phenolic chemical structure and particularly through the steric hindrance

brought by the alkyl side chain has been reported to be a suitable compound for antioxidant

applications, especially for petroleum products. Nevertheless, the antioxidant activity of non-

modified hydrogenated cardanol and cardol compounds was very low in comparison to

commercial antioxidant compounds such as butyl hydroxyl toluene (BTH).58 In consequence,

various modifications of cardanol were reported (Figure I - 25) attesting of its efficiency as

radical scavenger.

The alkylphenol synthetized by Rios et al.59 (A1, Figure I - 25) by alkylation of hydrogenated

cardanol was reported to reduce the formation of oxidation products in mineral lubricant oil

(MLO). Differential Thermal Analysis (DTA) of mineral lubricant oil with various antioxidants

such as cardanol-based 5-n-pentadecyl-2-tert-butylphenol (A1) and currently used 2,6-di-t-

butyl-4-methylphenol (BHT, an alkylphenol) and IRGANOX® (a diphenyl phosphate) are

summarized in Table I - 7. The higher degradation temperatures were recorded for MLO

modified with the cardanol-based antioxidant, Tmax = 246 °C, justifying its effective antioxidant

properties.

Sample Ti (°C, air) Tmax (°C, air)

MLO 91 225

MLO + 1 % A1 171 246

MLO + 1 % BHT 164 221

MLO + 1 % IRGANOX 166 230



temperature.)

The antioxidant effect of cardanol-based organophosphate compounds (A2, Figure I - 25) in

mineral lubricant oil (MLO) was also studied.60 The organophosphate antioxidant compound (A2)

was synthetized by alkylation of hydrogenated cardanol, followed by reaction with diethyl

chlorophosphate. Its antioxidant effectiveness was demonstrated by DTA measurements of MLO

with the cardanol-based phosphate compound and compared to MLO with alkylphenol and

diphenyl phosphate antioxidants (Table I - 8).

The antioxidant effectiveness of cardanol-based phosphate compound is proven by the higher

initial thermal degradation temperature (Ti = 156 °C) than for mineral oil without antioxidant (Ti

= 91 °C). Furthermore, its antioxidant effectiveness is comparable to those of current alkylphenols

or diphenyl phophates. The good thermo-oxidative stability of cardanol-based phosphate

compound can be explained by the bulkier substituent on ortho and para positions, increasing

42

the structures conjugation. Further studies on cardanol-based phosphate antioxidants

compounds (A4 and A5, Figure I - 25) reported similar results, and confirmed their efficient

antioxidant action for mineral oils.61

Sample Ti (°C, air) Tmax (°C, air)

MLO 91 226

MLO + 1 % A2 156 204

MLO + 1 % alkylphenol 178 239

MLO + 1 % diphenyl phosphate 152 201



temperature.)

With the aim of combining the antioxidant properties of hydroxyl 4-thiaflavane compounds and

the amphiphilic property of cardanol, Amorati et al.62 proposed the synthesis of a cardanol-based

4-thiaflavane anti-oxidant (A3, Figure I - 25) by Diels-Alder reaction. The rate constants for the

reaction with peroxyl radicals were measured by studying the autoxidation of styrene

(monitoring of the oxygen consumption) at 30 °C in presence of the synthetized antioxidant

compounds. The cardanol-based 4-thiaflavane antioxidant (A3) appeared very efficient because

it displayed rate constants, for reaction with peroxyl radicals, from 50 to 70 times higher than

hydrogenated cardanol, independently from the medium used to run the measures (Table I - 9).

kinh/105 M-1s-1

Measurement

medium

Styrene/PhCl Styrene/H2O H2O/PhCl

Cardanol 0.1 0.1 1

A3 (R = H) 7.0 5.2 0.7

A3 (R = CH3) 7.0 5.3 0.9

Table I - 9. Inhibition rate constants (kinh) obtained by studying the AIBN initiated autoxidation

of styrene at 30 °C in homogeneous solution using chlorobenzene (PhCl) as a solvent, or in a

two-phases water/styrene system.62

4 Cardanol-based polymers

Due to its particular chemical structure, cardanol is used as a building block for the synthesis of

many different polymer materials such as phenolic or epoxy resins, as well as polybenzoxazines

or polyurethane thermosets. The three available reactive sites on cardanol enable the synthesis

of numerous kinds of cardanol-based polymers. Furthermore, the presence of the C15 alkyl chain

43

endows hydrophobic properties to the material as well as flexibility on account of internal

plasticization.

4.1 Phenolic resins

One of the most considered applications of cardanol is its use as phenolic precursor for novolac

or resole type resin. Indeed, cardanol can undergo condensation with formaldehyde at ortho or

para position of the phenolic ring to form cardanol-formaldehyde (CF) resins (Figure I - 26).63

Figure I - 26. Synthesis of cardanol-based phenolic resin.63

The presence of the alkyl side chain increases hydrophobicity and results in highly flexible

materials with lower mechanical properties than usual phenol-formaldehyde resins. As a

consequence, cardanol-formaldehyde resins are barely used alone, but mainly in blends with

phenol-formaldehyde resins to obtain materials with good toughness.28, 64, 65

Some studies also reported the substitution of formaldehyde by furfural - a bio-based heterocyclic

aldehyde obtained from agricultural waste - and the synthesis of cardanol-furfural resins (Figure

I - 27). The replacement of formaldehyde by furfural promotes the thermal stability of the

phenolic resin. Indeed, according to the TGA results, cardanol-furfural resins display a higher

thermal stability as cardanol-formaldehyde resins. The furfural moiety of cardanol-furfural resins

was shown to be thermally more stable than the methylene bridge of cardanol-formaldehyde

resins.66

Figure I - 27. Condensation of cardanol with furfural and para-hydroxyacetophenone.66

44

4.2 Polyurethane resins

Polyurethanes (PU) are mainly used as coatings, adhesives and flexible or rigid foams. They are

obtained by the reaction of a polyol with a di- or polyisocyanate (Figure I - 28).

Figure I - 28. Synthesis of a polyurethane.

Cardanol is a good precursor for the synthesis of polyurethane resins considering its easy

conversion to polyol compound. The most current modification to obtain polyols from cardanol

relies on the reaction of the cardanol hydroxyl group or by condensation on the phenolic ring.

Furthermore, previous researchers reported the use of cardanol derivatives for the elaboration

of PU materials with enhanced thermal and mechanical properties. PU resins exhibiting good

thermal and mechanical properties were obtained for example from pre-synthetized cardanol-

formaldehyde resins,67-70 or from cardanol-furfural resins.71 Nevertheless, direct synthesis of

cardanol-based diols or polyols was also considered for the elaboration of cardanol-based PU

materials. These syntheses are detailed in the following paragraphs.

4.2.1 Synthesis of cardanol-based polyols

Cardanol-based diols (Figure I - 29) have been synthetized by reaction of cardanol hydroxyl

group with 3-chloropropane-1,2-diol,72 with epichlorohydrin,73 or by condensation of p-

aminophenol on cardanol.69 The two first syntheses resulted in the formation of aliphatic diols

while the third approach aimed at forming a molecule bearing two phenol moieties.

45

Figure I - 29. Chemical structures of cardanol-based diols a)72 b)73 c)69.

Cardanol-based polyols can also be synthetized by condensation reaction on the phenolic ring,

for example by reaction with oxazolidine (Figure I - 30),74 or with melamine and di-ethanolamine

(Figure I - 31).75

Figure I - 30. Synthesis of cardanol-based polyol by reaction with oxazolidine.74

The Mannich polyols synthetized by Ionescu et al. (Figure I - 31) were found to have a lower

viscosity (viscosity range of 3 to 5 Pa.s at T = 25 °C) than petrochemical Mannich polyols from

phenol and nonyl-phenol (25-30 Pa.s at T = 25 °C). Cardanol-based Mannich polyols were used

for the elaboration of rigid polyurethane foams with good mechanical and fire retardancy

properties. The Tg of the PU foams were found to be in the range of 110-120 °C. Thermal

degradation starts around 250 °C.

46

Figure I - 31. Synthesis of cardanol-based polyols by reaction with melamine and di-

ethanolamine.75

Flame retardant polyol with low viscosity were synthetized from reaction between cardanol,

melamine and di-ethanolamine (Figure I - 31).75 Rigid polyurethane foams were then elaborated

by reaction of the synthetized polyols with poly-isocyanates as curing agents and cyclopentane

as blowing agent. The introduction of the flame-retardant melamine moiety in the molecular

structure of cardanol-based polyol enhanced the thermal stability and the flame resistance of the

PU materials.

Low viscosity cardanol-based polyols were obtained by Suresh et al.73 exhibiting various range of

hydroxyl functionality values (Figure I - 32).

Figure I - 32. Synthesis of cardanol-based polyols by reaction with epichlorohydrin and

diethanol amine or with glycerol monochlorohydrin.73

47

For instance, a Cardanol-based triol was synthetized by epoxidation of the cardanol hydroxyl

group followed by a reaction with diethanol amine. Another type of cardanol based triol

compound was synthetized by the reaction between cardanol and glycerol monochlorohydrin.

The obtained polyols were characterised by a low viscosity. The corresponding PU materials

(with diphenyl methanediisocyanate) were rigid and exhibit good mechanical and thermal

properties with Tg = 98 °C.

Another way to synthetize polyols from cardanol is the chemical modification of the alkyl chain

unsaturations. Primary hydroxyl groups can be easily grafted onto the cardanol side chain either

by performic acid oxidation (Figure I - 33),76 or by thiol-ene coupling with 2-mercaptoethanol

(Figure I - 34).77

The cardanol-based polyols synthetized by Suresh et al. 76 (Figure I - 33) were evaluated in the

preparation of rigid polyurethane foams by reaction with 1,4-diazabicyclo[2.2.2]octane. Their

mechanical and viscoelastic properties were comparable to PU foams elaborated from

commercial polyols.

Figure I - 33. Synthesis of cardanol-based polyols by performic acid oxidation.76

The polyols from cardanol synthetized by Fu et al. 77 (Figure I - 34) were used for the elaboration

of PU materials by reaction with hexamethylene diisocyanate. The thermal properties of the

corresponding PU materials are gathered in Table I - 11.

48

Figure I - 34. Synthesis of cardano-based polyols by thiol-ene coupling with 2-

mercaptoethanol.77

Two kinds of polyols were synthetized from cardanol: CAP1 and CAP2 represented in Figure I –

34. The highest Tg was obtained for the PU foam from CAP1 with Tg = 31.6 °C, wheras for CAP2 Tg

= 16.1 °C (Table I – 10). The lower Tg of PU material from CAP2 compared to PU material from

CAP1 is probably due to the long carbon chain introduced on the phenolic hydroxyl group and

increasing the flexibility of the polymer chains. The degradation temperatures showed no

remarkable difference because the degradation process is mainly attributed to the cardanol chain

scission.

Sample Tg (°C) T10% (°C) Tmax (°C)

CAP1 31.6 302.5 346

CAP2 16.1 291.8 333

Table I - 10. Thermal of CAP1 and CAP2 based PU materials.77 (T10% is the temperature at 10

wt% weight loss and Tmax is the temperature at maximum rate weight loss).

4.2.2 Cardanol-based non-isocyanate PU

The handling of isocyanate raw materials and their use for the production of polyurethane

products has become an issue due to the high toxicity of isocyanate. In this context, the

development of non-isocyanate polyurethanes through the reaction of amines and cyclic

carbonates is of growing interest. The synthesis of cashew nutshell liquid (CNSL)-based urethane

polyols via a non-isocyanate route has been reported.78 Cyclic carbonate derivative of diglycidyl

ether of cardanol was obtained by addition reaction of high pressure CO2 followed by reaction

with primary hydroxylamines yielding to the formation of hydroxyl and urethane groups (Figure

49

I - 35). The so-synthetized polyols were then cured using hexametoxy methylene melamine as

hardener yielding PU materials.

Figure I - 35. Synthesis of CNSL-based urethane polyols via a non-isocyanate route.78

4.3 Epoxy resins

Epoxy resins are well-known high performance thermosets used in numerous applications such

as coatings, adhesives, composite matrix etc. due to their good thermo-mechanical, chemical and

electrical properties.79 The actual concern about the use of petroleum-based phenolic compounds

for chemical applications encouraged researchers to develop sustainable alternatives, among

them various modifications and the use of cardanol as epoxy pre-polymer were reported in the

literature.

Di- or poly-epoxy monomers from cardanol are commercially available (Cardolite – NC-514), and

are synthetized through a two-step reaction with cardanol as starting reagent (Figure I - 36). The

studies based on these monomers are detailed in Chap IV- 1.

Figure I - 36. Chemical structure of diglycidyl ether of cardanol – commercially available NC514

- from Cardolite Corporation.

50

Most of the time cardanol epoxidation is used for the enhancement of the properties of cardanol-

formaldehyde phenolic resins. Indeed, their properties can be improved by additional

polymerization of the epoxy groups. Furthermore the reaction of the epoxy group with various

compounds such as with carboxyl-terminated polybutadiene allows the enhancement of the

impact resistance of the resin (Figure I - 37).20-22

Figure I - 37. Proposed reaction between epoxy groups of cardanol and carboxyl-terminated

polybutadiene.22

Kanehashi et al. suggested the synthesis of epoxy pre-polymers from cardanol by epoxidation

with epichlorohydrin in basic conditions of the cardanol hydroxyl group, followed by a thermal

polymerization of the cardanol alkyl side chain double bonds. (Figure I - 38).25 Epoxy coating

materials are afterwards obtained by reaction/curing with various diamines at room

temperature.

Figure I - 38. Synthesis of epoxidized cardanol pre-polymer.25

Finally, an enzymatic synthesis was proposed as a green approach for the epoxidation of Cardanol

(Figure I - 39).80 The unsaturations of the alkyl chain were epoxidized by reacting with lipase in

the presence of acetic acid and hydrogen peroxide, prior to form a polymer with epoxy-

functionalized pending C15 chains through coupling of the phenol moieties with peroxidase and

hydrogen peroxide. Peroxidase was shown by the authors to polymerize meta-substituted

phenols such as cardanol with chemical selectivity. Peroxidase was thus used to obtain

polycardanol and epoxide-containing cardanol. During the epoxidation by lipase/H2O2/acetic

acid, some polycardanols are crosslinked due to highly oxidative environment. The amount of

crosslinked polycardanols is higher for the polymer (Route B) than for the monomer (Route A).

The route A rather the route B is thus recommended to produce epoxide-containing

polycardanols as prepolymer.

51

Figure I - 39. Synthesis of epoxidized cardanol and polycardanol. 80

Finally the as-synthetized prepolymers were cured with a phenalkamine to elaborate the final

crosslinked material. Film samples of 50 µm thickness were prepared on a glass slide. The

hardness of the resulting materials measured by pencil scratch technique revealed that the

hardness improved with increasing epoxy content suggesting that the epoxy groups play a major

role in the materials hardness. Epoxide-containing polycardanols reached the highest hardness

of 9 H when cured for 5 h at 150 °C, a higher value compared to a commercially available alkyl

resin coating at 4 H. Furthermore, the addition of a phenalkamine curing agent still enhanced the

hardness to the material up to 5 H within 2 h curing. Epoxide containing polycardanol resins were

thus demonstrated to be a viable bio-based alternative to phenol-formaldehyde resins for

applications requiring high hardness and mechanical durability.

4.4 Polybenzoxazine resins

Polybenzoxazine (PBz) resins are another class of high performance thermoset materials. They

are emerging since three decades, and due to their outstanding properties and to their mono-

component resin status, they are considered as promising substitutes to phenolic or epoxy resins.

Polybenzoxazine resins are obtained through the ring-opening polymerization of benzoxazine

(Bz) monomers. The synthesis of benzoxazine monomers is based on a Mannich-like reaction

between a phenolic compound and formaldehyde, followed by a ring-closure process on a

phenolic derivative (Figure I - 40).81

52

Figure I - 40. Synthesis of a benzoxazine monomer.81

Through its phenolic structure, cardanol appears as a suitable bio-based phenolic compound for

the synthesis of Bz monomers. Indeed, several works report the use of cardanol for the synthesis

of novel bio-based Bz monomers and their corresponding PBz materials. The studies dealing with

these cardanol-based monomers and thermosets are detailed in Chapter III.

5 Conclusion

This first chapter highlights that cardanol is an important industrial crop that can be used for

many applications. Furthermore, the presence of different reactive sites (phenol, unsaturation

etc.) makes it as versatile chemical platform to design a wide range of molecules with high added-

value applications such as surfactants, antioxidants or plasticizers to polymer precursors. In

particular, due to its intrinsic properties, cardanol has been widely used for the synthesis of bio-

based surfactants and for the elaboration of phenolic, epoxy, or polyurethane materials. More

recently, the use of cardanol for the design of benzoxazine monomers is gaining more and more

interest, since it tackles several issues frequently encountered with benzoxazine monomers such

as high melting temperatures or the high brittleness of the resulting polybenzoxazine materials.

The following chapters are highlighting various chemical modification strategies we designed to

access new cardanol-based derivatives to be used for the elaboration or reinforcement of

polymeric materials.

The chapter II deals with the synthesis of reactive ammonium cardanol-based surfactants and the

study of their reactivity for the preparation of clay composite materials with BADGE. In the

chapter III a new strategy for the elaboration of bio-based and processable Bz materials by

combining cardanol with other naturally occurring phenolics is reported and studied. Finally the

use of Bz resins for the macromolecular reinforcement of a cardanol di-glycidyl ether resin by the

elaboration of interpenetrating polymer networks will be investigated.

53

Chapter II: Surfactants from cardanol

1 Introduction

Due to its naturally amphiphilic structure, cardanol is an excellent candidate for the preparation

of surfactants, as it has been detailed in Chapter I – 3.2. Indeed, surfactants are amphiphilic

molecules constituted of a hydrophobic part (the tail) and a hydrophilic group (the head). The

C15 alkyl side chain provides an essential hydrophobicity while the slightly polar hydroxyl group

allows a wide variety of chemical functionalization.82 Notwithstanding this particularly adequate

structure, cardanol-based surfactants are just emerging as a green alternative to conventional

petroleum-derived nonylphenols for the preparation of surfactants.4, 30, 31, 44-49, 51 Surfactants are

largely used as detergents, wetting and/or foaming agents, emulsifiers or dispersants due to their

ability to lower the surface tension of a liquid, between two liquids or between a liquid and a solid.

They are also largely used as clay organomodifier for the elaboration of clay-polymer

nanocomposite materials. In the present chapter, we aimed at synthesizing new ammonium

cationic surfactants from cardanol displaying different reactivities. Then we studied their effect

on the exfoliation of Montmorillonite clay within Bisphenol A diglycidyl ether (BADGE) epoxy

thermoset for the elaboration of composite materials. A state-of-the-art about the elaboration of

silicate layered polymer composite materials, the compatibilization between clay minerals and

polymer materials (clay organomodification) as well as the choice of the surfactant kind will be

introduced in the following part.

1.1 Preparation of nanocomposite materials

With the aim of improving polymeric materials properties, numerous researchers studied the

dispersion of compatible inorganic materials within the polymeric matrix. The addition of

particles as fillers leads to improvement of the material thermal, mechanical or conductive

properties such as stiffness and toughness, barrier effect or fire resistance. A large range of

natural and synthetic fillers are available for their elaboration. (Table II – 1).83

54

Chemical nature Filler examples

Element Graphite

Metal chalcogenides (PbS)1.18, (TiS2)2, MoS2

Carbon and Carbon oxides Graphite, Graphite oxide, Carbon Nanotubes

Metal phosphates Zr(HPO4)

Clays and layered silicates Montmorillonite, hectorite, saponite,

fluoromica, fluorohectorite, Vermiculite, kaolinite, magadiite

Layered double hydroxides M6Al2(OH)16CO3·nH2O, M=Mg, Zn

Other Nanocellulose, Nanochitin

Table II - 1. Example of fillers for the elaboration of nanocomposites.83

The pioneer work of the Toyota research group (1990) on polyamide 6 reinforced with

alkylamonium-modified Montmorillonite (MMT)84, 85 opened the gate to the use of clays and

layered silicates as polymer fillers. More particularly, polymer-layered crystal nanocomposites

are a class of composite materials. These materials are obtained by the intercalation of the

polymer within the particles layers. Such materials can be defined as nanocomposites when the

dispersed clay particles are sized in the range of nanometres (Less than 100 nm). It is noteworthy

that a homogeneous dispersion of clay is essential to an efficient reinforcement of a composite.

The percentage of clay needed to enhance the thermal and mechanical properties of polymer

layered silicate nanocomposite is very low (2 to 5 wt %). As a consequence, a great advantage of

these materials is their light weight.

Among the possible polymeric materials available for the elaboration of nanocomposites, the

study of epoxy based polymeric matrix has been significant. Indeed, epoxy thermosets are

broadly used in adhesives and coatings. Nevertheless, high performance applications are hardly

reached with non-modified epoxy thermosets.79 The elaboration of epoxy composites, by the

incorporation of layered silicate filler particles, was shown to lead to an enhancement of the

materials properties86 and was thus widely studied. 83, 86-90 The mechanical properties of lamellar

silicate-modified epoxies are strongly dependent on the fillers size, organophilic treatement and

on their intercalation/exfoliation state within the final material.79

1.2 Structure and properties of clay and layered silicates as fillers

Clay and lamellar silicates, especially the smectite type - 2:1 clay minerals - are widely available

and the most commonly used as natural fillers. More particularly, MMT clays have several assets

which justify their wide use: a high cation exchange capacity (CEC, meq/100g), a multiscale

organization (Figure II - 1a), good swelling properties in water and a large surface area.91, 92 The

distinctive structure of MMT clay consists in platelets each composed of two tetrahedral silica

55

sheets -SiO4- framing an octahedral alumina sheet -Al(OH)3- (Figure II - 1b), separated by

metallic cations.

Figure II - 1. Schematic representation of a) MMT multi-scale organization,93 and b) MMT

crystallographic structure.89

Through isomorphic substitutions of structural ions within the MMT sheets, a charge deficiency

is created. Indeed, some ions within the platelet sheets can be replaced by lower charged ions.

For instance, Al3+ can be replaced by Fe2+ or Mg2+. The MMT platelets are thus globally negatively

charged. Consequently, exchangeable counter-ions are present in the interlayer space between

the platelets in order to insure the clay platelets electro-neutrality. The nature of the cations and

their hydration are mostly determining the interlayer dimension. The interlayer distance

between two platelets is described as a basal spacing d001. In the case of MMT clay the interlayer

cations are essentially hydrated Na+ and Ca2+, conferring a hydrophilic character to the MMT clay.

As polymeric materials, such as epoxies, are generally characterised by a hydrophobic behaviour,

the modification of the clay minerals hydrophilic property is essential for adequate matrix-filler

compatibility. Indeed, the properties of nanocomposite materials are strongly impacted by the

morphology and the filler dispersion state within the polymeric matrix.83, 94 Depending on the

polymer-clay compatibility several dispersion states can be obtained (Figure II - 2).83

56

Figure II - 2. Schematic representation of a) phase separated microcomposites, b) intercalated

nanocomposites, and c) exfoliated nanocomposites.

Phase separated composites are obtained (Figure II - 2a) when the polymer is not able to

intercalate the MMT sheets. Aggregates or tactoids of primary particles of MMT are dispersed

within the polymeric matrix and a microcomposite-like behaviour is observed. An intercalated

state (Figure II - 2b) is reached when the polymer is able to spread between the clay platelets

layers, increasing the basal distance by keeping an ordered structure with alternate layers of clay

and polymer. The exfoliated state (Figure II - 2c) is obtained when the polymer is able to

intercalate the clay platelets layers or when monomers are intercalated between the clay platelets

prior their polymerization. The clay layers become totally independent and the crystallographic

orientation is lost. Both intercalated and exfoliated states correspond to nanocomposite materials

with an improvement of the corresponding neat polymeric material properties. Nevertheless, the

exfoliated state appears to be the most efficient in terms of mechanical and barrier properties

enhancement95, 96 and a particular attention has been paid to the understanding of the exfoliation

mechanism of lamellar silicates, especially for MMT clay.97, 98 Indeed, in order to obtain an

exfoliated structure it is essential to enhance the clay-polymer compatibility and to promote

either the intercalation of the polymer chains or the in-situ polymerisation of monomers within

the interlayer space. The surface modification of the clay mineral by an organic compound

(organomodification) represents a widely studied approach.88, 99

57

1.3 Clay organomodification strategies

Elaboration of MMT nanocomposites by direct polymer intercalation is hardly reached due to

their discordant properties. Indeed, most of the polymers are hydrophobic whereas pristine MMT

clay is hydrophilic due to the presence of hydrated metallic cations within the sheets interlayer

space. The elaboration of MMT nanocomposites requires thus the clays organomodification. For

the last two decades, many works report on the investigation of MMT exfoliation mechanism in

polymers and how to drive them.94, 98, 100

Through its particular structure composed of lamellar sheets, the MMT modification to

hydrophobic/more organophilic compound is easily achievable. Clay organomodifications can be

achieved predominantly by two processes: (1) a non-covalent grafting (by a cationic exchange of

the interlayer cations with cationic surfactants) or (2) a covalent grafting (reactive groups

towards the polymer are bonded on the edge or on the surface of the clay platelets).101

In the following part, we will mainly focus on the clay organomodification strategies for the

reinforcement of epoxy resins.

1.3.1 Clay organomodification by cationic exchange reaction

MMT clay organomodification is generally achieved by cation exchange reaction. Indeed, the

interlayer cations insuring electronegativity of the materials are easily exchangeable, particularly

with organic ammonium or phosphonium-based surfactants.100, 102, 103 These alkylammonium or

alkylphosphonium cations allow lowering the surface energy of the clay minerals galleries and

the wetting properties of polymer matrices towards the organomodified MMT are thus improved.

The most used cationic surfactants for the organomodification of MMT clay as filler for epoxy

nanocomposites are ammonium-based surfactants, particularly quaternary ammonium ones.

Indeed, the hydration of quaternary ammoniums is lower than those of primary ammoniums and

their desorption is thus minimized. Notwithstanding, an exfoliated state is hardly reached if an

additional chemical catalysis is not provided.104 Indeed the polymer growing or networking

kinetics must be higher within the clay mineral interlayer spaces compared to outside otherwise

there might be a rate competition between the platelets exfoliation and the polymer matrix

gelation during polymerization.105 Indeed, when the polymerization rate is higher in the

interlayer galleries than in the outside, the formation of an intragallery polymer network is firstly

initiated and the limited polymer network (outside the clay interlayer) remains sufficiently

mobile to facilitate further migration of the monomers into the clay interlayer galleries for further

exfoliation. In the case of epoxy as polymeric matrix, a correlation has been found between the

surfactant Lewis acidity and a catalytic growth of the epoxy network, favouring the clay mineral

layers separation (exfoliation) in the following order: CH3(CH2)17NH3+ > CH3(CH2)17N(CH3)H2+ >

58

CH3(CH2)17N(CH3)2H+ > CH3(CH2)17N(CH3)3+.105, 106 Primary ammonium surfactants are thus

favouring the clay exfoliation within an epoxy matrix through acid catalyses, whereas quaternary

ammonium surfactants tend to lower hydration and desorption of the surfactants. This

correlation highlights the difficulty to select the appropriate type of surfactant.

Figure II - 3. Schematic representation of the monomer inclusion within MMT, followed by in-

situ polymerization to reach MMT exfoliation.

Furthermore, the exchange between interlayer cations and organic surfactants allows not only

the clay modification from a hydrophilic to a hydrophobic character but also the modification of

the interlayer spacing. Indeed, the interlayer distance is also an essential parameter to consider

for the elaboration of nanocomposite materials. Actually, most of the nanocomposite materials

are elaborated by direct intercalation of polymers from solution or melts within the clay

interlayer space, as well as by the inclusion of monomers that polymerize in the interstice (Figure

II - 3).101

The formation of exfoliated clay nanocomposites is strongly dependent on the nature of the

alkylammonium cations. Indeed, longer linear alkyl chains facilitate the formation of

nanocomposites. 8 to 15 carbon long alkyl chains surfactants are essential to adequately push

apart the clay mineral layers to allow the polymer chains or monomers to diffuse within the clays

galleries and to obtain an exfoliated state. Lan et al. 107 reported the organomodification of MMT

clays with ammonium surfactant of different alkyl chain length and the elaboration of

nanocomposite materials with BADGE cross-linked by Jeffamine D2000. They highlighted the

relation between the ammonium clay organomodifier chain length and the clay exfoliation.

Indeed, in the case of MMT clay modified with CH3(CH2)7NH3+, the clay galleries hydrophobicity

is relatively low and the interlayer space is narrow. The amount of intercalated epoxide and

amine cross-linker is thus insufficient to achieve exfoliation. The phase dispersed in the

59

composite resulting from CH3(CH2)11NH3+ organomodified MMT and the epoxy matrix is a

mixture of exfoliated clay platelets and clay primary particles. On the contrary, MMT clay

organomodified with CH3(CH2)17NH3+ surfactant allowed the intercalation of epoxide monomers

and amine cross-linkers within the clay interlayer galleries, and lead thus to the formation of

exfoliated clay platelets based nano-composite.

1.3.2 Clay organomodification by cationic exchange reaction and covalent grafting

Beside the compatibility enhancement provided by the cationic exchange with surfactants, clay

minerals could also be made compatible towards epoxy precursors. Indeed, when the clay is

modified with amine, anhydride or carboxylic groups for instance, the epoxy monomers could

react with the reactive groups and the polymer network could grow within the interlayer space.79

To this aim, several researchers modified MMT clay for instance by covalent grafting of

organosilane compounds with various functionalities onto the hydroxyl groups on platelet

surfaces or edges. The grafted organosilanes may be reactive toward epoxy polymers for example

if they are bearing amine, anhydride or carboxylic groups.108-111

Nevertheless, Le Pluart et al.108 highlighted the possible reaction of covalent grafted

organosilanes on the layer edges between themselves leading to a collapse of the mineral layers

and preventing their exfoliation. The clay organomodification by cationic exchange prior to the

covalent grafting of functionalized organosilane compounds should be favoured. Indeed, the prior

organomodification would increase the interlayer spacing, helping thus the diffusion of the

organosilane compounds (and afterward epoxy monomers) within the interlayer space and

favouring thus their covalent grafting on the platelets surfaces and afterwards the platelets

exfoliation.

As described previously, the clay organomodification by a cationic surfactant is essential to

change the clay hydrophilic character to a more organophilic character, as well as to enhance the

clay platelets interlayer space. On the other hand, the covalent grafting of functionalized

organosilane compounds onto the clay platelets allow the easy introduction of reactive functions

towards epoxy compounds, favouring their polymerization within the clay platelets.

Le Pluart et al. proposed the modification of MMT clay by combination of cationic exchange and

covalent grafting reactions.108 The MMT clay interlayer space and hydrophobic property were

modified by the introduction by cationic exchange reaction of dimethylbenzylammonium

surfactants. The MMT clay was then further modified by the grafting of amino-silane compounds

-reactive towards epoxy polymers- onto the hydroxyl groups situated on the surfaces and edges

of the MMT clay platelets (Figure II - 4).

60

Figure II - 4 Grafting of an amino-silane compound on prior organomodified MMT clay.108

Nevertheless, surfactants could also bear other reactive functions and could thus be able to take

part in polymerization reactions with various polymer kinds. This strategy developed by Pluart

et al. paved the way to a convenient clay organomodification method by modifying clay minerals

through the incorporation of reactive surfactants. This strategy is studied in the following work.

1.4 Cationic surfactants from Cardanol

As described previously, mostly cationic surfactants are used for clay organomodification by

cationic exchange reaction. To date, only two studies on cardanol-based cationic surfactants were

reported in the literature. A hydrogenated cardanol-based quaternary ammonium with the

quaternary ammonium placed at the end of the alkyl chain was synthetized and used as a phase

transfer catalyst (Figure II - 5).49

Figure II - 5. Chemical structure of cardanol-based quaternary ammonium surfactant from De

Avellar et al.49

Verge et al. 51 reported the synthesis of a cardanol-based ammonium surfactant (Figure II - 6)

from the commercially available cardanol mono-epoxy derivative NC-513 (Cardolite

Corporation).

61

Figure II - 6. Synthesis of cardanol-based ammonium surfactant from the cardanol mono-epoxy

derivative NC-513.51

This surfactant issued from cardanol was particularly appropriate to enhance the compatibility

between sepiolite, a needle-like clay mineral, and conventional Bisphenol A diglycidyl ether (1,4-

diaminocyclohexane - DAC - as hardener). The specific structure of the cardanol-based surfactant

enabled the modification of sepiolite clay through cation exchange reaction. Furthermore, free

NH2 and OH reactive groups on the surfactant allowed the reaction with epoxy monomers onto

the clay surface, improving the compatibility between clay and epoxy and promoting the growing

of the polymer network between the sepiolite needles. Thus, the organomodification of sepiolite

clay by the cardanol-based surfactant (PkH+) led to a good dispersion of the clay needles within

the BADGE polymeric matrix, in comparison to non-modified sepiolite clay (SEM analysis, Figure

II – 7).

Figure II - 7. Scanning Electron Micrographs of BADGE/DAC polymer network filled with a) 5

wt% neat sepiolite and b) 5 wt% sepiolite organomodified by PkH+.51

Moreover, the good dispersion of sepiolite clay needles within the polymeric matrix led to an

enhancement of the material thermo-mechanical properties. Indeed, the Tg was shifted to higher

temperature (from 180 °C to 195 °C) and the storage modulus was increased from 4.0 to 4.8 GPa

at 50 °C.

62

Based on these previous results, three different ammonium surfactants were prepared from

epoxidized cardanol NC-513. In a first time the effect of the cardanol-based surfactants on the

Montmorillonite clay organomodification was investigated. Then, their amino group content and

reactivity towards the BADGE epoxy matrix were studied as a benefit or a drawback to the

exfoliation of MMT layered clay mineral within a BADGE epoxy matrix. Indeed, the surfactant

activity towards BADGE could either help the MMT layer exfoliation or even aggregate those.112

These results are presented in the following section.

2 Results and discussion

The detailed experimental conditions are reported in annex p181.

2.1 Surfactants synthesis

As described in the previous part, keeping an amino-multifunctionnality is essential to promote

the clay oragnomodification in a first time, and the polymer growth within the clay platelets in a

second time. Primary and secondary amine groups available within the surfactant would allow

the grafting of epoxy compounds within the organomodified clay, improving thus the polymer

intercalation and growth within the clay. This first part, focused on the amino-multifunctionnality

of cardanol-based surfactants, specially tailored to highlight the surfactant reactivity–to–clay

exfoliation relationship. Three surfactants were prepared from an epoxy derivative of cardanol

(NC-513) with amino compounds of different amine functionalities toward epoxies.

The same conditions were applied to synthetize each surfactant (Figure II - 8). The cardanol-

based surfactants were synthetized through nucleophilic addition of a primary amine on the

epoxide group of NC-513 in chloroform. The amine was added in excess to the media in order to

favour the mono-addition of cardanol on the amine compound. Indeed, it is preferred to keep the

maximum of reactive (free) primary and secondary amine functions on the surfactant so that they

may be able to react once they are incorporated to the clay. Depending on the amine functionality,

cardanol-based surfactants CardS1, CardS2 and CardS3 were synthesized.

Tris(2-aminoethyl)amine (TAEA) was used as reagent for the synthesis of the CardS1 surfactant

with a functionality of 5 (f = 5) (because two free primary -NH2 functions accounting for 4 and

one secondary -NH function are available, accounting for 1). The use of ethylene diamine (EDA)

allowed the synthesis of the CardS2 surfactant with a functionality of 3 (f = 3) (one free -NH2 and

one free -NH functions). Finally, the CardS3 surfactant with a functionality of 1 (f = 1) was

synthetized with N,N-dimethylethylenediamine (DMEDA) (one free –NH function). The synthesis

and the chemical structures of the surfactants are displayed on Figure II - 8.

63

A family of novel cardanol-based ammonium surfactants, with increasing amino functionalities

towards epoxy, were thus synthetized: CardS1 (f = 5) > CardS2 (f = 3) > CardS3 (f = 1).

Figure II - 8. Schematic representation of the synthesis of the Cardanol-based surfactants.

2.2 Characterization of CardSx surfactants

2.2.1 Fourier Transform Infrared spectroscopy (FTIR)

The FTIR spectra of CardS1, CardS2 and CardS3, are depicted in Figure II - 9a, b &c respectively.

The FTIR spectra of all CardSx materials were very similar, as expected due to their close chemical

structure.

64

Figure II - 9. FTIR spectra of a) CardS1, b) CardS2, c) CardS3.

The characteristic peaks of the cardanol compound were observed, especially aromatic C-H

stretching at 3009 cm-1, strong CH2 and CH aromatic and aliphatic absorption band at 2927-2854

cm-1 arising mainly from the long alkyl chain and aromatic C-H out of plane deformations at 1637

cm-1. In addition, characteristic peaks of amine functions were also observed, such as N-H

stretching absorption band at 3287 cm-1, C-N stretching at 1101 cm-1, and the ethers C-O

stretching at 1048 cm-1.

2.2.2 Characterization by 1H NMR

1H NMR characterization was achieved to further confirm chemical structures of the cardanol-

based surfactants. The quantitative results for each CardSx compound are reported and the NMR

spectra are depicted in Figure II - 10 for the case of CardS1 and in the Figure II - 11 and - 12 for

CardS2 and CardS3 respectively.

65

The signal due to the aromatic protons at δ= 6.50-7.25 ppm was used as integration reference for

4H. The expected theoretical integrations were calculated by moderation based on the abundance

of unsaturation described in the literature.11 Nevertheless, cardanol-based products are

composed of four molecules differing by the unsaturation degree of their alkyl chains. These

unsaturation abundances can slightly vary regarding the origin and the processing of the CNSL

based bio-product for the manufacturing of NC-513. The assignments depicted in Figure II - 10

are based on a previous work50 and from a study on Cardanol-issued polyurethane resin

described in reference.70 To simplify, the experimental and theoretical integrations will be noted

Iexp and Ith respectively.

The NMR spectrum of CardS1 is displayed in Figure II – 10.

Figure II - 10. CardS1 1H NMR spectrum (Solvent CDCl3).

For each surfactant, the characteristic peaks of cardanol were observed, especially the aromatic

protons [1, 2, 3, 4] at 7.15 and 6.75 ppm (used as integration reference), the alkyl chain olefinic

CH2 protons [b2, d2, e2, g2, h2, a2] at 5.81, 5.35, and 5.03 ppm, the protons in α of the alkyl chain

unsaturations [c2, f2, i2] at 2.04 ppm, as well as the CH2 protons in α of the aromatic [o] at 1.59

ppm, the CH2 from the alkyl chain [b1, c1, d1, e1, f1, g1, h1, i1, j, k, l, m, n] at 1.31 ppm and the CH3 of

the alkyl chain at 0.91 ppm. The CH2 of the alkyl chain comprised between two unsaturations [c3,

f3] were detected at 2.28-2.95 ppm, together with CH2 protons from the used amine moiety. The

experimental and theoretical integrations of the CardS1 peaks are reported in the Table II - 2. As

66

it can be observed, the experimental integrations of the peaks corresponding to the cardanol

moiety were close to the expected integrations for a mono-addition of NC-513 on TAEA.

Beside the characteristic peaks from the cardanol moiety, the reaction of the NC-513 epoxy group

with the TAEA amine to yield CardS1 was confirmed by the presence of peaks at 3.84-4.23 ppm

corresponding to H in α to oxygen [5, 6]. Their integration corresponds to an opened epoxy cycle

as they integrated for Iexp = 3.5 H (Ith = 3 H). Furthermore, peaks corresponding to the TAEA

compound were also readily observed. The peaks at 2.28-2.95 ppm, Iexp = 15.6 H, Ith = 16.1 H,

corresponded to the CH2 [7, 8, 9, 10, 11] of TAEA combined to the CH2 between two unsaturations

of NC-513 [c3, f3]. The primary amines of TAEA [12] appeared at 3.4 ppm with Iexp = 4.3 H (Ith = 4

H), confirming the mono-addition of NC-513 on one TAEA moiety.

Chemical shift

(ppm) Assignment Iexperimental Itheoretical

0.91 Alkyl chain CH3 1.8 H 1.7 H


1.59 -CH2-Ar 2.3 H 2H

2.04 -CH2*=CH- 3.4 H 3.1 H

2.28 – 2.95

Amine moiety –CH2-

and cardanol moiety

=CH-CH2*-CH=

15.6 16.1

3.04 -NH2 4.3 4

3.84 – 4.23 H in α to O 3.5 3

4.93 – 5.90 Alkyl chain CH= 4.8 4.5

6.68 – 7.21 H-Ar 4 4

Table II - 2. CardS1 experimental and theoretical integrations.

The characteristic peaks from the cardanol moiety were also observed for the CardS2 compound

(Figure II – 11). The experimental integrations were very close to those of the theoretical

integrations and to the integrations found for CardS1. (Table II - 3)

The mono-addition of NC-513 on EDA was confirmed by the integrations and the presence of te

peaks at 3.86-4.30 ppm, Iexp = 3.4 H, Ith = 3 H, corresponding to reacted epoxy ring protons in α of

oxygens [5, 6], the peaks at 2.47-2.93 ppm corresponding to the CH2 [7, 8, 9] of EDA combined to

the CH2 between two unsaturations of NC-513 [c3, f3] for which Iexp = 8.5 H and Ith = 8.1 H, and the

peak at 3.18 ppm, Iexp = 2.5 H, Ith = 2H corresponding to the NH2 of EDA [10].

67


Chemical shift




1.61 -CH2-Ar 2.2 H 2H

2.04 -CH2*=CH- 3.3 H 3.1 H

2.47 – 2.93


and cardanol moiety

=CH-CH2*-CH=

8.6 8.1

3.18 -NH2 2.5 2

3.86 – 4.30 H in α to O 3.4 3

4.90 – 5.93 Alkyl chain CH= 4.7 4.5

6.64 – 7.25 H-Ar 4 4


Finally for the CardS3 compound, the peaks corresponding to the cardanol moiety were also

observed on the NMR spectra, and their integrations were consistent with a mono-addition of NC-

513 on an amine compound such as for CardS1 and CardS2. (Table II - 4).

68

The mono-addition of NC-513 on DMEDA was further confirmed by the following peaks: the CH2

[7, 8, 9] of DMEDA combined to the CH2 between two unsaturations of NC-513 [c3, f3] for which

Iexp = 13.6 H and Ith = 14.1 H, the protons of reacted epoxy ring protons in α of oxygens [5, 6] at

3.86-4.30 ppm, Iexp = 3.4 H, and Ith = 3 H.


Chemical shift




1.61 -CH2-Ar 2.2 H 2H

2.04 -CH2*=CH- 3.6 H 3.1 H

2.47 – 2.93


and cardanol moiety

=CH-CH2*-CH=

13.6 14.1

3.86 – 4.30 H in α to O 3.4 3

4.90 – 5.93 Alkyl chain CH= 4.9 4.5

6.64 – 7.25 H-Ar 4 4


For all the characterized compounds, the experimental integrations were slightly varying from

the expected integrations. This is due to the fact that cardanol is a natural-occurring compound

69

with diverse compositions, which lead to complex NMR spectra. Nevertheless, the number of

aromatic protons is a good reference because only the cardanol is bearing aromatic protons. Thus

for a mono-addition of NC-513 on TAEA for example, only 4 aromatic H should be observed. In

the present case, the estimation of 4 aromatic H as integration reference seemed to be correct, as

4.53 aromatic H were integrated for the integration of the global CardS1 corresponding spectrum

(Total number of proton: exp = 54.67 / th = 55).

In conclusion, the NRM spectra and the integrations let pretend to a majority of mono-addition of

NC-513 on the different amine-containing molecules, confirming the structures of the synthetized

surfactants obtained by IR characterization.

2.2.3 Characterization by MALDI-TOF/MS

The chemical structures of the three synthetized surfactants were further characterized by

MALDI/TOF-MS analysis. The surfactant experimental mass could thus be compared to the

expected mass in order to fine-tune their chemical structure.

In order to characterize the molecules, α-cyano 4-hydroxycinnamic acid (CHCA) was used as

protic matrix for MALDI-MS analysis. By using this matrix, only the protonated molecule should

be detected.

Cardanol is a product composed of four different molecules, varying through their alkyl chains

unsaturation degree. As a result, the MALDI-MS spectrum obtained from compounds synthetized

from cardanol displayed a fingerprint pattern, allowing the easy recognition of cardanol-

containing compounds by MALDI-MS analysis.51 For example, in the case of the CardS1

compound, synthetized with TAEA (M = 146 g/mol), a peak spreading from 501 to 507 m/z was

expected for the mass peak of a mono-addition of TAEA on the epoxidized cardanol [CardS1+H]+.

Indeed, the molar mass of NC-513 is varying from M = 354 g/mol and M = 360 g/mol, depending

on the alkyl side chain unsaturation degree.

For each surfactant, the MALDI-MS analysis in Figure II – 13a, c & e gave rise to an intense peak

assigned to the mono-addition of the epoxy derivative of cardanol (NC-513) moiety onto the

amine-containing reagent (chemical formula in Figure II – 8). For instance, the MALDI-MS

analysis of the CardS1 compound revealed as expected the mono-addition of NC-513 on TAEA, as

the corresponding peak could be observed at 501 m/z (Figure II – 13a). Similarly, the mono-

addition of NC-513 on EDA (CardS2) and DMEDA (CardS3) were confirmed by the presence of the

corresponding peaks at 415 and 443 m/z respectively.

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The mass for each Cardanol-based surfactant were in accordance with their expected structure,

and the protonated mono-addition compounds of NC-513 on the various amine-containing

reagents were the main detected compounds.

Figure II - 13. MALDI-MS spectra of CardS1 using a) CHCA & b) DCTB as matrix, CardS2 using

c) CHCA & d) DCTB and CardS3 using e) CHCA & f) DCTB as matrix.

In addition, to the MALDI-MS analyses with CHCA as protic matrix, MALDI-MS analysis using

Trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) as matrix

were also achieved and are reported in Figure II - 13b, d & f.

Additional MALD-MS analyses using DCTB as matrix were achieved in order to validate the

structural features of the obtained surfactants and to highlight their available amine

functionalities. Indeed, DCTB is known to react with primary and secondary amines both in

solution and in the gas phase, to produce molecule-matrix adducts, characterized by +184 Da

shifted peaks (proportionally to the number of N-H bonds).113 In this reaction, an amino group of

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the surfactant replaces the dicyanomethylene group of DCTB forming a matrix adduct via a -C=N-

bond (Figure II – 14). As DCTB is not a protic matrix, silver (Ag) was added to the molecule-

matrix mixture in order to protonate them for their detection.

Figure II - 14. Proposed mechanism for DCTB adduction to an aliphatic primary amine.113

These side reactions with DCTB were readily observed here for all the three surfactants in

satisfactory accordance with their structures and the content of amino groups. DCTB was only

able to react four times on CardS1 (f = 5) with characteristic peaks observed at 685.5 m/z [CardS1

+ H + 1 x 184 Da], 869.7 m/z [CardS1 + H + 2 x 184 Da], 1237.9 m/z [CardS1 + H + 4 x 184 Da].

Nevertheless, the fifth addition of DCTB on CardS1 could be expected for this compound. This last

reaction was probably impeded by the sterical hindrance. An amine functionality of f = 4 will thus

be considered for CardS1 in the rest of this study. The DCTB matrix reacted as expected three

times on CardS2 (f = 3) and one time on CardS3 (f = 1) characterized by the peaks observed at

599.5 m/z [CardS2 + H + 1 x 184 Da] and 967.7 m/z [CardS2 + H + 3 x 184 Da] for CardS2 and at

627.5 m/z [CardS3 + H + 1 x 184 Da] for CardS3.

These characterizations by MALDI-MS analysis using DCTB as matrix corroborated the

surfactants structures identified with CHCA matrix, and further validated their amine

functionalities.

In conclusion, MALDI-MS analyses confirmed both the mass of the expected chemical structures

and the amine functionalities of the synthetized cardanol-based surfactants. The effective amine

functionalities available on each surfactant can be summarized as follow: CardS1 (f = 4) > CardS2

(f= 3) > CardS3 (f = 1).

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2.3 MMT clay organomodification and characterization

2.3.1 O-MMT preparation procedure

MMT clay is widely used for the reinforcement of epoxy thermosets and was thus chosen for the

elaboration of composite materials. As described previously, MMT is a hydrophilic compound,

whereas epoxy compound is hydrophobic. In order to improve the epoxy-clay compatibility, it is

essential to modify the hydrophilic MMT to a more hydrophobic compound. This modification of

the MMT hydrophilic property can be achieved by its organomodification by the pre-synthetized

ammonium cardanol-based surfactants.

Each of the synthetized surfactant was used for the organomodification of MMT by standard

cation exchange procedure. 2 mole equivalent in regards to the MMT’s Cationic Exchange

Capacity (CEC = 116 g/mol) were used for the organomodification procedure.

In a first step, the surfactants (2 equivalents to the MMT’s CEC) were protonated in an EtOH/HCl

solution. The protonated surfactant solution was added in a second step to the MMT clay (1

equivalent), previously dispersed in H2O. The obtained O-MMT was filtrated and washed with

ethanol/water solution, and further freeze-dried. The protonation is known to preferably occur

on tertiary and secondary amines (more basic than primary amines). The resulting O-MMT

products are noted CardS1-MMT, CardS2-MMT and CardS3-MMT.

2.3.2 Characterization of O-MMT by X-ray diffraction (XRD)

With the aim to confirm the MMT organomodification by cationic exchange reaction, XRD

characterization was carried out. The exchange between the MMT interlayer cations and the

synthesized surfactants should modify the interlayer spacing. So, the interlayer distance has been

tracked on MMT and O-MMT by XRD analysis (Figure II - 15).

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Figure II - 15. X-Ray diffractograms of pristine MMT and O-MMT.

The XRD diffractogram of non-modified MMT showed a diffraction peak at 2θ = 7 ° (d = 12.6 Å).

The diffractograms of O-MMT showed all diffraction peaks at lower angles: 2θ = 4 ° (d=22.1 Å),

2θ = 4.2 ° (d=21 Å), 2θ = 4.5 ° (d=19.6 Å) for CardS1-MMT, CardS2-MMT and CardS3-MMT

respectively (Figure II - 15), meaning that the interlayer spaces were quite similar for each clay

mineral as expected due to the close chemical structures of each surfactant.

In conclusion, the interlayer spacing increasing from 12.6 Å for the pristine MMT to around 20-

22 Å for the O-MMT witnessed the efficient ion exchange between interlayer cations and

cardanol-based surfactants, confirming thus the efficient MMT-organomodification.

2.3.3 Characterization of O-MMT by MALDI-TOF/MS

The O-MMT clay was characterized by MALDI-MS (DCTB-Ag matrix) to verify that the surfactant

was present within the clay platelets. Indeed, after the clay organomodification by cationic

exchange, the surfactants should be present within the clay platelets in their protonated form.

The clay platelets are not protonated, and thus not detected by MALDI-MS.

As compared to the native surfactants, the MALDI analyses (DCTB-Ag matrix) of O-MMT resulted

in completely different mass spectra (Figure II – 16).

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Figure II - 16. MALDI-MS spectra, using DCTB-Ag as matrix, of a) CardS1-MMT, b) CardS2-

MMT, and c) CardS3-MMT.

As depicted on Figure II - 16a for CardS1-MMT, the protonated surfactant was readily detected

within the MMT clay at m/z 501. As mentioned earlier, DCTB is known to react with primary and

secondary amines both in solution and in the gas phase, to produce molecule-matrix adducts,

characterized by +184 Da shifted peaks (proportionally to the number of N-H bonds).

Nevertheless, a unique +184 Da mass shift (addition of DCTB) was observed. Indeed, the presence

of amonium function was shown to reduce or fully avoid the DCTB side reaction.113 In comparison,

for neat CardS1 (not within the clay), the protonated specie was poorly detected and an amine

functionality of f = 4 was found because 4 additions of DCTB on the molecule were detected (Chap

II, 2.2.3; Figure II - 14). Both observations were thus in accordance with the presence of species

of CardS1 protonated prior to the mixing with the DCTB matrix and any irradiation and mass

analysis. In consequence, it can be concluded that the CardS1 surfactant was present in its

protonated form within the MMT clay. Similar results were obtained for MMT-CardS2 and MMT-

CardS3 (Figure II - 16b and - 16c respectively), both of them were detected as protonated

species at m/z 415 and 443, respectively, while the reaction with DCTB was completely avoided

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(no +184 Da mass shift). The CardS2 and CardS3 surfactants were thus also shown to be present

in a protonated form (prior to irradiation and mass analysis in presence of DCTB) within the MMT

clay.

In conclusion, the XRD analysis of the O-MMT revealed increased interlayer spacing, conveying

the effective organomodification of the clay by the three surfactants. Furthermore, the three

surfactants were found by MALDI-MS analysis to be present in their protonated form within the

O-MMT clay, further confirming the efficient clay organomodification by the synthetized

surfactants. Nevertheless, the fact that the surfactants were in their protonated form within the

O-MMT clay and that they do not further react with DCTB suggest a different reactivity towards

the BADGE epoxy – i.e. the available amino functionalities (AAF).

2.4 Evidence of the surfactant amino-multifunctionnality within MMT clay

The MALDI-MS (DCTB-Ag matrix) analyses results of the surfactants within MMT clay (CardS1-

MMT, CardS2-MMT, and CardS3-MMT) supposed a change in the surfactant available amine

functionalities. Indeed, their protonated form seemed to influence on the availability of the amine

functions of the surfactants to further react with the BADGE epoxy. In order to determine the

available amine functionality of the surfactants (free to further react with epoxy matrix) once

incorporated within the MMT clay, a mono-functional furfuryl glycidyl ether (Fge, Figure II - 17)

was added to the O-MMT clay.

Figure II - 17. Chemical structure of furfuryl glycidyl ether (Fge).

The epoxy group of Fge is supposed to react with the neutral primary and secondary amines of

the surfactants (Figure II - 18).

Figure II - 18. Reaction between epoxy and primary and secondary amine functions.

The detection by MALDI-MS analysis of the amount of Fge compound grafted on each surfactant

will allow the determination of the number of available amine functions free to react with epoxy

groups in each O-MMT.

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Following the addition of Fge, the Fge-grafted surfactants were characterized by MALDI-MS

analysis using DCTB-Ag as matrix. As Fge was added directly to the O-MMT clays, the surfactants

were thus in their protonated form and thus no longer able to react with DCTB (Chapter II, 2.3.3).

In consequence, in these experiments no CardSx – DCTB adduct were anymore expected. This

characterization allows to track the available amine content of the surfactants (means the free

primary and secondary amines), highlighted by the CardSx – Fge adducts potentially detected.

The resulting MALDI-MS spectra are depicted on Figure II - 19.

Figure II - 19. MALDI-MS spectra of Fge-grafted a) CardS1-MMT, b) CardS2-MMT, and c)

CardS3-MMT using DCTB-Ag as matrix.

Three additions of the Fge mono-epoxy on CardS1-MMT were readily detected: mono-addition at

m/z 655.5, di-addition at m/z 809.5, tri-addition at m/z 963.6) (Figure II – 19a). These results

were expected as f = 4 for CardS1. Indeed, because Fge only reacts with neutral amines, three

77

available amine functionalities (AAF = 3) are quantified for CardS1-MMT (CardS1 in its

protonated form within MMT).

Similarly, in the case of CardS2-MMT two additions of Fge were detected (AAF = 2) in Figure II –

19b, at m/z 569 (mono-addition) and m/z 723.6 (di-addition), as expected from protonated

CardS2 (f = 3).

For CardS3-MMT (Figure II – 19c) the protonated surfactant was readily detected at m/z 443.4

as the major product, indicating that the protonated CardS3 surfactant within MMT was not able

to react with Fge. However, a unique addition of Fge is surprisingly detected at m/z 597. This

addition of Fge was not expected from the CardS3 composed of a secondary and a tertiary amine

(f =1). Indeed, the protonated surfactant should not be able to react anymore as the protonation

is known to preferably occur on secondary amines (more basic than primary amines).

Nevertheless, the low abundance of this peak revealed the very poor reactivity of CardS3 towards

Fge. The mono-addition product of Fge on CardS3-MMT could be explained by the reactivity of

the secondary amine towards Fge in its neutral form, influencing the protonation equilibrium.

In conclusion, CardS3-MMT seemed not to be able to react with epoxy groups because the

protonated CardS3 specie was in majority detected. A higher reactivity towards Fge was observed

for the CardS2-MMT and CardS1-MMT samples, as the protonated surfactants were no longer

detected in the associated MALDI-MS spectra (expected at m/z 415 and 501 respectively). Indeed,

the detection of the Fge-grafted surfactants within O-MMT clay by MALDI-MS analysis confirmed

that the synthetized CardS1 and CardS2 surfactants contained available amine functionalities free

to react towards epoxy after the organomodification procedure. Furthermore, the expected

difference of the surfactants reactivity related to their amine content and nature could also be

observed. Indeed, the protonated CardS1 compound (f = 4) was able to react three times with Fge,

and protonated CardS2 (f = 3) reacted two times with Fge. As expected, the CardS3 compound (f

= 1) reacted almost not with Fge. The surfactants could thus be classified according to their

available amine functionalities (AAF) able to further react with epoxy after organomodification:

CardS1 (AAF = 3) > CardS2 (AAF = 2) > CardS3 (AAF <1).

2.5 Preparation and characterization of CPN materials

2.5.1 CPN preparation procedure

Clay mineral-based polymer nanocomposite (CPN) with conventional diglycidyl ether of

Bisphenol A (BADGE) were prepared to validate the impact of the available amine functionalities

of surfactants onto the MMT exfoliation. It is worthy to remind that the CPN with MMT or O-MMT

78

were prepared thanks to a simple magnetic stirring without any additional dispersion or

exfoliation enhancement.

Composite materials, composed of BADGE epoxy cured by diaminocyclohexane (DAC) and

including 10 wt% of O-MMT organomodified by CardS1, CardS2 or CardS3, were elaborated and

their morphology as well as their properties were investigated. A 10 wt% pristine MMT/BADGE

composite was also prepared as a reference.

2.5.2 CPN characterization by X-ray diffraction (XRD)

The effect of the MMT organomodification on the interlayer space between the clay platelets was

previously characterized. The interlayer distance was shown to increase from 12.6 Å (pristine

MMT) to around 20 Å regardless to the used surfactant.

In the following part, the relationship between amino-functionnalities of the surfactant reactive

towards epoxy within the clay and their effect on the MMT clay intercalation or exfoliation within

the BADGE polymer matrix were studied. To this aim, the composite materials were characterized

by XRD analysis.

X-ray diffractograms of the CPN are reported on Figure II – 20. First of all, it can be noted that a

diffraction peak from 2θ = 10 ° to 2θ = 20 °, due to BADGE, was observed in each diffractogram of

CPN materials.

Figure II - 20. X-ray diffractograms of CPN prepared with 10 mass% of pristine and

organomodified MMT by CardS1, CardS2 and CardS3.

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For the reference pristine MMT/DEGBA CPN, the MMT diffraction peak was located around 6 °,

corresponding to a 15 Å interlayer distance between the MMT clay platelets and indicating that

the clay was not exfoliated. Furthermore, the XRD analysis of the raw MMT (Chap. II – 2.3.2)

indicated an interlayer distance of 12.6 Å. It can be concluded that the epoxy polymer barely

intercalated the pristine MMT.

In the case of the diffractograms corresponding to O-MMT/BADGE CPNs, a clear trend appeared

concerning the MMT clay dispersion state. Indeed, in the case of CardS3 (AAF < 1), a clear

intercalated structure was obtained with a diffraction peak at 3.2 ° (corresponding to an

interlayer length of 28 Å) in comparison to CardS3-MMT (2θ = 4.5 °, dCardS3-MMT = 19.6 Å). The shift

of the diffraction peak to lower angles indicated that the monomers were able to diffuse within

the clay platelets. However, because the CardS3 surfactant did not present enough available

amine functionalities to allow its reaction with the epoxy matrix the exfoliation of platelets during

polymerization did not occur.

When CardS2 was used to organo-modify MMT (with an expected AAF of 2), a partially exfoliated

structure was observed as depicted by the shoulder located around 2.2 ° (d = 40 Å). The clay was

partially exfoliated within the epoxy matrix and some intercalated clay aggregates were still

present. Finally, when CardS1 (with an expected AAF of 3) was used, no diffraction peak was

observed above 2 ° indicating that an exfoliated state tended to be reached.

The effect of the reactivity – i.e. the amine available functionality content - of the surfactants on

the exfoliation of clay within an epoxy polymer matrix was demonstrated. The clay

organomodification by the surfactant with the higher available amine functionnalities (CardS1,

AAF = 3) led to an exfoliated state, whereas the surfactants with lower AAF resulted in partially

exfoliated or intercalated states (CardS2 (AAF = 2) and CardS3 (AAF < 1) respectively).

2.5.3 CPN Thermal characterisation

DSC characterization of BADGE/O-MMT CPN materials elaborated with MMT clay

organomodified by the most reactive surfactant CardS1 was carried out with the aim to determine

the effect of the clay exfoliation on the final materials thermal properties.

In a first time, the epoxy thermoset BADGE cured with 1,2-diaminocyclohexane (DAC) in

stoichiometric proportions was prepared as a reference (BADGE/DAC). Then, epoxy

nanocomposite materials with various amount of MMT were prepared. BADGE/MMT

nanocomposite materials were elaborated with 5 %, 7% or 10 % of pristine MMT, labeled

hereafter CPN5%, CPN7% and CPN10% respectively. The effect of the BADGE/ MMT ratio was

then investigated by the DSC analysis (Figure II – 21).

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pristine MMT.

As observed by XRD analysis on Figure II - 17, materials elaborated from BADGE and pristine

MMT led to composite materials where the dispersed MMT clay was aggregated. Indeed, the MMT

diffraction peak around 6 ° was readily observed, indicating that the MMT was not intercalated

or exfoliated within the elaborated epoxy materials. Nevertheless, as it could be observed on the

DSC thermograms displayed on Figure II - 21, the addition of pristine MMT to BADGE/DAC epoxy

thermoset allowed an increase of the materials Tg. It was shifted from 170 °C for the BADGE/DAC

reference to 200 °C for CPN7% and CPN10% and to Tg = 205 °C for CPN5%. The classical polymer-

inorganic filler interaction must be responsible for this polymer chain mobility hampering and so

the Tg increased.114

In the same way, BADGE/O-MMT (modified by CardS1) nanocomposite materials were

elaborated with 5 %, 7 % or 10 % of CardS1-MMT, labeled hereafter CPN-OMMT5%, CPN-

OMMT7% and CPN-OMMT10% respectively. The corresponding DSC thermograms are displayed

in Figure II - 22.

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MMT modified by CardS1.

The surfactant CardS1 was demonstrated to be the most reactive surfactant towards the BADGE

epoxy leading to an exfoliated structure of the O-MMT clay within the epoxy matrix. The

nanocomposite structure of those materials was confirmed by the absence of MMT diffraction

peak on the XRD diffractogram (Figure II – 20). The thermal properties of the CPN-OMMT5%,

CPN-OMMT7% and CPN-OMMT10% nanocomposite materials were thus expected to be different

from their counterpart composite based on aggregated MMT. Despite an exfoliated structure of

the O-MMT clay, the Tg of the nanocomposite materials were found to decrease when compared

to the materials with pristine MMT clay. Indeed, the measured Tg were decreasing from Tg = 170

°C for the BADGE/DAC to Tg = 165 °C, 150 °C and 130 °C for CPN-OMMT5%, CPN-OMMT7% and

CPN-OMMT10%, respectively. The Tg are decreasing with increasing amount of O-MMT, and thus

increasing amount of cardanol-based surfactant. As the MMT is modified by a cardanol-based

surfactant, this effect may be attributed to a predominating plasticizing effect induced by the

cardanol alkyl side chain. This phenomenon could furthermore be attributed to

homopolymerization of the epoxy monomers triggered by the presence of cationic compounds,

decreasing thus the materials crosslinking density. Indeed, for the material elaborated with

pristine MMT, the materials Tg were observed to increase with the presence of pristine MMT (Tg

= 170 ° C for BADGE/DAC and Tg = 205°C, 200 °C, 200 °C for CPN5%, CPN7% and CPN10%,

respectively), despite the aggregate state of the pristine MMT clay within the epoxy matrix.

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2.5.4 CPN characterization by SEM and EDX analyses

Morphological observations with scanning electron microscopy (SEM) were performed to

confirm XRD analyses about the extent of the clay exfoliation in the polymer matrix. The use of

the most reactive surfactant CardS1 for the clay organomodification was shown to result in

exfoliated clay within the BADGE epoxy matrix. On the contrary, an intercalated structure was

achieved for the materials obtained from the clay modified with the less reactive surfactant

CardS3. In order to compare the two structures, the SEM analyses were performed on the

BADGE/CardS1-MMT CPN and BADGE/CardS3-MMT CPN materials. On Figure II - 23 are

reported a) topographic micrographs, b) chemical contrast micrographs and c) aluminium

mapping of MMT-CardS3 (above pictures) and MMT-CardS1 (bottom pictures) CPN. As a

reminder, MMT contains aluminum oxide in its crystal structure. SEM images were recorded on

fractured samples.

Figure II - 23. I) Scanning electron micrographs of the fracture of MMT-CardS3 (above part)

and MMT-CardS1 (bottom part) based CPN. a) corresponds to the topographic micrographs, b)

to the chemical contrast (BSE detector, the lightest the points and the heaviest the elements)

and c) is the aluminium distribution of the analysed area

II) Element composition obtained for analyses of an aggregate (EDS1) and unfilled area (EDS2).

(EDS3) corresponds to the homogeneous area

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In the case of CardS3 based CPN, large aggregates (several tenth µm) were visible on the

topographic micrographs (Figure II – 23a, above part). Local energy dispersive X-Ray analyses

(EDX) measurements were carried out in order to identify the aggregates (Figure II – 23b, above

part, EDS1). The aluminum distribution (Figure II – 23c, above part) and the local EDS

measurements clearly evidenced that the aggregates were mainly composed of Al, main

components of alumino-silicate clay minerals. EDX measurements performed on areas without

aggregates (Figure II – 23b, above part, EDS2) were mainly composed of C and O, corresponding

to the chemical composition of the epoxy matrix.

In the case of the CardS1-based CPN (Figure II – 23a, bottom part), a homogeneous structure

was observed. Aluminum mapping (Figure II – 23c, bottom part) indicated that the element was

uniformly distributed all over the surface of the observed fracture. Whatever the part analyzed

by EDX, a similar composition was observed (an example is reported on Figure II – 23b, bottom

part, EDS3).

SEM/EDX analyses were in good adequacy with XRD measurements: the use of the less reactive

surfactant CardS3 resulted in composite materials with clay aggregates within the polymer

matrix, and no trace of exfoliated clay (no trace of Al) was found in the areas free of aggregates.

On the contrary, the use of the most reactive surfactant CardS1, with high amino group content,

led to an exfoliation of platelets-like clay minerals in epoxy, as the Si and Al compounds were

homogeneously present within the BADGE/CardS1-MMT material.

3 Conclusions

This study dealt with the synthesis of three bio-based surfactants and the comparison of their

different reactivity on the dispersion of MMT in epoxy. The surfactants were synthesized from a

glycidyl ether derivative of cardanol, a C15-alkylphenol. Three amines were used to modify the

cardanol-issued molecule, differing by the number of available amine groups Tris(2-

aminoethyl)amine (TAEA), ethylene diamine (EDA) and N,N-dimethylethylenediamine

(DMEDA), yielding to surfactants with different amount of reactive functionalities towards epoxy.

CardS1 synthetized from NC-513 and TAEA has an amine functionality of 4 (f = 4) as evidenced

by the formations of 4 adducts with DCTB observed by MALDI-MS characterization. Similarly,

CardS2, the product of the reaction between NC-513 and EDA, was shown to have 3 reactive

amine functionalities (f = 3), and CardS3 synthetized from EDA and NC-513 showed the lower

amine functionality content with f = 1.

X-ray diffractograms and MALDI-TOF/MS were used to evidence the success of the

organomodification as the interlayer space was demonstrated to increase with the presence of

the cardanol-based surfactants. Nevertheless, due to their close chemical structure, the uses of

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the three cardanol-based surfactants led to roughly the same interlayer distance between the

platelets.

In sum, a deeper clay exfoliation was expected during epoxy-amine polymerization process giving

the nanocomposite material at the end. That is why the available amine functionality content of

each surfactant, once situated within the MMT clay, was investigated. Indeed, as it could be

observed by MALDI-MS analysis, the surfactants seemed to display a different reactivity

according to their environment (without or within the clay platelets). To verify the available

amine functionality content of the surfactants within the clay, furfuryl glycidy ether (Fge)

compound was grafted to the surfactants, and the Fge-grafted surfactants were detected by

MALDI-MS characterization. As expected, more Fge units were grafted to the surfactants with

higher amino group content. Nevertheless, available amine functionality (AAF) of the surfactants

within the clay were found to be lower than those of the neat surfactants: CardS1 (AAF = 3) >

CardS2 (AAF = 2) > CardS3 (AAF < 1). Clay mineral-based polymer (CPN) with conventional

diglycidyl ether of bisphenol A were then prepared with the three O-MMT.

Lower glass transition temperatures than for the reference BADGE/DAC materials were observed

when O-MMT modified by CardS1 was added. Indeed, the addition of MMT clay modified by

cardanol-based surfactants seemed to lower the materials properties due to the plasticizing effect

of the cardanol alkyl side chain and homopolymerization of the epoxy monomers induced by the

presence of cationic species. Still, the introduction of O-MMT clay modified by cardanol-based

surfactants may be an innovative way to increase the flexibility of some brittle thermosets such

as polybenzoxazines.

Finally, it was concluded thanks to XRD and SEM analyses coupled with energy dispersive X-ray

analyses that the reactivity of the surfactants led to an enhancement of the dispersion of MMT

platelets. No diffraction peak was observed by XRD when the most reactive surfactant (CardS1)

was used to modify MMT, while a clear intercalated structure was evidenced for the surfactants

with the lowest amino group content (CardS2 and CardS3). Similarly, SEM/EDX evidenced a

better dispersion of O-MMT platelet when using CardS1. This cardanol-based surfactant was thus

efficient for promoting both ion exchange and exfoliation of the clay platelets; it is thus a good

candidate for Montmorillonite clays dispersion.

The efficiency of the synthetized cardanol-based surfactants on the clay exfoliation on a

Bisphenol-A based epoxy matrix was highlighted in this work. The approach of modifying MMT

clay by a bio-based surfactant could further be applied to bio-based epoxy matrices in order to

lower the carbon footprint of the materials and to tend to the elaboration of fully bio-based high

performance materials.

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Chapter III: Benzoxazines from cardanol

1 Introduction

Benzoxazines (Bz) gained a great interest due to their huge potential to overcome several short-

coming of conventional novolac and resole-type phenolic resins while keeping clear assets. Di-

functional benzoxazines (di-Bz) are widely studied since the last two decades and the growing

number of new benzoxazine (Bz) structures attest the clear benefit that represents its versatile

chemical design. Indeed, the versatility in the chemical structure of Bz monomers comes from

large variety of phenolic and amino-based compounds available. With the growing trend to

producing environmentally-friendly and high performance materials derived from renewable

resources, the use of bio-based phenolic derivatives for the synthesis of Bz monomers is

considered as a viable alternative to petroleum-based phenolic counterparts. Under this trend,

several reports have studied the use of bio-based phenolic compounds such as cardanol, vanillin,

eugenol, etc.… for the synthesis of mono- or di-functional Bz monomers. Nevertheless, the

processability (melting and shaping) of these monomers remains generally difficult due to too

close melting and polymerization temperatures. An interesting approach for acting on the Bz

monomers processing windows consists in the versatile synthesis of asymmetric di-Bz

monomers using for example a diamine as bridging group between cardanol and a second

phenolic derivative. It yields in a lowering of the melting temperature in comparison to the

symmetric monomers. This proposal is expounded in this chapter.

1.1 Benzoxazine thermosets

1.1.1 Generalities

Thermoset polymers are mainly represented by phenolic, epoxy or bismaleimide resins. These

polymers are well known for their high performance applications due to notable thermal and

mechanical properties, good chemical resistance and flame retardation. However, these high

performance multicomponent thermosets suffer from significant shortcomings such as high

brittleness as well as the formation of voids and by-products during curing. Benzoxazine resins –

namely polybenzoxazines (PBz) – are a new class of thermoset polymers emerging since several

decades and are considered as a promising substitution of phenolic or epoxy resins. Indeed, in

addition to properties similar to those of phenolic or epoxy resins,115, 116 PBz are also

characterized by low water absorption,115 high char yield116 and near-zero volumetric shrinkage

or expansion during polymerization.117, 118 Benzoxazine monomers are synthesized through a

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Mannich-like condensation of a phenolic derivative, a primary amine (aliphatic or aromatic) and

formaldehyde, followed by a ring-closure process (Figure III - 1).81, 119

Figure III - 1. Classical two-step approach for the synthesis of mono-benzoxazine monomers.120

Mono-benzoxazine monomers (m-Bz) are gathering the monomers composed of one benzoxazine

group, in opposition to di-benzoxazine monomers (di-Bz), composed of at least two benzoxazine

moieties (Figure III - 2). Di-Bz monomers can be synthetized from various starting reagents,

either from a diphenolic compound (1eq) with a primary amine (NH2-R) (2eq) and

paraformaldehyde (4eq), or from a diamine compound (NH2-R-NH2) (1eq) with a phenol

derivative (2 eq) and paraformaldehyde (4 eq).

Figure III - 2. Chemical structure of a) mono-benzoxazine (m-Bz) and b) di-benzoxazine (di-Bz)

monomers.

87

1.1.2 Benzoxazine polymerization

Polymerization of Bz monomers – generally 1,3-benzoxazine isomers121 – is achieved by

thermally-induced auto-catalysed ring-opening polymerization (ROP) (Figure III – 3), avoiding

therefore the use of strong acid catalysts and/or the formation of by-products.118

Figure III - 3. Thermally-induced ring opening polymerization of Bz monomers.120

Thus PBz resins are advantageously mono-component resins, compared to phenolic or epoxy

resins. Indeed, Bz ROP occurs without the use of catalyst in a temperature frame of 160 °C to 220

°C. Bz monomers contain a small amount of impurities such as phenolic raw materials and

oligomers, allowing the initiation of the polymerization as the temperature arise. The

polymerization is then auto-catalysed by the formation of phenolic compounds through the

monomer ring-opening.118

Depending on the structural nature of the Bz monomers, either linear or cross-linked polymers

are obtained. It has been shown that Bz monomer polymerization preferentially occurs at the

ortho position of the hydroxyl function (Figure III – 3).119, 122, 123 Polymerization of m-Bz typically

leads to low weight linear polymers around a few hundreds to a few thousands g/mol.123

Especially for m-Bz monomers from para-substituted phenolic compounds, it was demonstrated

that the polymerization was self-terminated after a single ring-opening. Indeed, the

polymerization was stopped at a dimer level by the formation of a six-membered ring between

the aza-methylene and the hydroxyl group of the phenolic ring (Figure III - 4).124, 125

88

Figure III - 4. Dimer product of para-substituted m-Bz monomer via ring-opening reaction.124

However, if the m-Bz phenolic ring is reactive enough, meaning additional polymerization

positions such as para positions are available, even m-Bz monomers could lead to cross-linked

PBz.120 Indeed, if the para and/or meta positions are available, they may also react in the

polymerization process. The reactivity reduces from ortho to para and from para to meta, which

is rather unreactive (Figure III - 5).120

Figure III - 5. Possible polymerization reactions sites in order the most to the least

predominant: 1 ortho, 2 para, 3 meta.120

Nevertheless, PBz from m-Bz monomers are usually low molecular weight materials due to

competition between thermal dissociation of the monomers and the chain propagation as

demonstrated by Reiss et al..123 On the contrary, di- or poly-functional Bz monomers lead almost

systematically to infinite molecular weight cross-linked polymers due to their higher

functionality.126, 127 The use of di-Bz monomers for the elaboration of high performance materials

is in consequence widely preferred to m-Bz monomers.

89

1.1.3 Effect of hydrogen bonding and π-π supramolecular interactions on polybenzoxazines

properties

Excellent properties were reported for PBz resins. Nevertheless Ishida et al.115 reported that,

despite displaying high Tg’s and high moduli, the crosslinking density of PBz resins remained very

low in comparison to epoxy resins. Generally, high glass transition temperature is in correlation

with the high crosslinking density. Wirasate et al.128 studied the dependency of various hydrogen-

bonding infrared modes to understand the hydrogen-bonded structure in the PBz resins. They

reported two types of hydrogen bonds within PBz materials. Both statistically distributed and

conformationally preferred hydrogen bonding may contribute to the stiffness of the system and

led to high Tg and high modulus polymer. The excellent properties of PBz resins have further been

attributed to the hydrogen bonds within the materials by several other studies.129-133

The reinforcement strategy of PBz resins generally relies on extensively used polymer fillers as

polyhedral oligomeric silesquioxanes (POSS),134-136 clay minerals,137-141 or carbon nanotubes.142-

146 Recent works on carbon nanotubes (CNT)/polybenzoxazines composites raised interests onto

convenient composites preparations based on π-π supramolecular interactions leading to good

reinforcement of the PBz materials.142, 143, 146 Nevertheless, the thermo-mechanical properties of

PBz/CNT composite materials were moderate and strongly dependent on the functionalization of

the CNTs fillers.136 Dumas et al.143 proposed the elaboration of PBz/CNT nanocomposites with

good thermo-mechanical properties through the facile and efficient dispersion of neat CNTs

within various Bz compounds: M1 (Bisphenol A/aniline based Bz monomer) and M2 (1,4-

phenylene diamine/phenol based Bz monomer) (Figure III - 6).

Figure III - 6. Chemical structures of the Bz monomers used for the elaboration of Bz/CNT

nanocomposites.143 – M1: Bisphenol A/aniline based Bz monomer and M2: 1,4-phenylene

diamine/phenol based Bz monomer.

For nanocomposite compounds containing 5 wt% of CNTs, the Tg and storage modulus of M1-

based PBz material remained unchanged, whereas a significant improvement was observed for

M2-based PBz materials. Indeed, the Tg of the M2-based PBz material was shifted by 50 °C to

90

higher temperatures, and the onset of its thermal degradation was shifted from 250 °C to 300 °C.

These results were correlated to strong supramolecular filler-matrix π-π interactions.

Regarding clay minerals, a traditional organomodification approach is employed to promote clay

dispersion in Bz. As defined in the previous chapter, this strategy relies on the exchange of the

clay inter-platelets cations by a reactive and organophilic cation to enhance the diffusion of Bz

monomers within the clay platelets galleries and therefore favouring the polymer growing to

reach an exfoliated state. 140, 141, 147, 148 Conscious of the strong interactions driving the properties

of PBz networks, it appears clear that using supramolecular interactions for the reinforcement of

PBz matrix is a facile and efficient strategy.

Motivated by these approaches and in order to study the interaction between pristine clay and

PBz resins, prior to clay organomodification, we proposed to study the supramolecular

interaction between kaolin and poly(EDBz).149 Indeed, kaolin is a common raw material which

main component is kaolinite, a 1:1 clay mineral composed of single layers with a SiO4 tetrahedral

network connected to Al(O, OH)6 octahedral networks with platy particle of hexagonal symmetry.

The layers are held together via hydrogen bonds, dipolar interactions and attractive Van der

Waals forces, which results in a low intrinsic inner surface reactivity. Isomorphic substitutions

within the layers generate negative charges that are counterbalanced by alkali cations (Na+ and

K+) situated at the interlayer. Such cations are known to catalyse Bz crosslinking reactions.150

Thus, due to its intrinsic interactions, kaolin appears as an adequate candidate to form

supramolecular assembly with Bz. Composite materials, containing 10 wt% of neat kaolin, were

elaborated. The FTIR measurements attested of the establishment of supramolecular H-bonding

interactions between EDBz and kaolin in the monomer melt, leading to fine clay dispersion into

the resin after polymerization, as evidenced by SEM analyses (Figure III - 7).

Figure III - 7. Representative SEM images of a) pristine kaolin and b) 10 wt% kaolin/EDBz.

Thanks to the promoted dispersion of kaolin driven by the H-bonding interactions, the thermal

and thermo-mechanical properties of the benzoxazine resins were significantly improved. For

instance, increases of the Tg from 161 °C to 171 °C, of the storage modulus from 3.4 GPa to 4.9

91

GPa and the thermal stability from 220 °C to 245 °C were triggered by the incorporation of 10

wt% of kaolin. The completed study is not detailed in this manuscript, please report to Ganfoud

et al.149 for additional information.

1.1.4 Polymerization catalysis

Even though the polymerization of benzoxazine monomers is thermally activated and auto-

catalysed by the formation of new phenolic compounds through the ring opening polymerization,

some initiators/catalysts may be added to trigger the polymerization of Bz monomers at lower

temperature.151-155 Wang et al.151 achieved a screening of the use of possible initiators and/or

catalysts for reducing the curing temperature and curing time of Bisphenol A/aniline - based Bz

monomers (BA-a). The polymerization of (BA-a) monomers with 5 mol% of various catalysts was

carried out at 20 °C during 20 h. The thermal properties of the Bz monomers cured in presence

of effective catalyst were investigated and compared to the properties of the thermally cured neat

(BA-a) material (Tg = 177 °C, Char yield = 30 %). It was observed that the use of some catalysts

for the polymerization resulted in materials with higher Tg and higher char yield. Particularly

when Lewis acids such as PCl5, PCl3, POCl3 and TiCl4 were used, Tg’s higher than 200 °C were

recorded. Furthermore, char yields around 50 % were recovered from TGA analysis. The use of

catalysts could thus be interesting for the elaboration of thermal protection materials. In

conclusion a broad variety of catalysts may be used for the ring opening polymerization of Bz

monomers at lower temperature.

Beside their effective catalyst activity, the majority of the catalysts appear to be petroleum-based

and/or toxic. MgCl2 and ZnCl2 were evaluated as a safer alternative and as new catalysts to reduce

the polymerization temperature of a (cardanol/aniline)-based Bz monomers, which usually

polymerize at elevated temperature (around 260 °C).156 As it can be observed in Table III - 1, the

use of 1 mol% of these catalysts enabled to significantly reduce the polymerization temperature,

even below 200 °C in the case of MgCl2.

Catalyst Polymerization

temperature (°C)

No catalyst 260.6

MgCl2 193.1

ZnCl2 207.1

p-TsOH 206.0

Table III - 1. Polymerization temperatures of (cardanol/aniline) PBz cured with 1 mol%

catalyst.156

92

Some researchers studied also the ring opening catalysis of Bz monomers by the addition of

catalytic functional groups on the monomers such as carboxylic acids.157, 158 Andreu et al.158

analysed the thermal polymerization behaviour of several carboxylic-containing Bz monomers

(Figure III - 8), and studied their effect on the polymerization temperature when used as co-

monomer with a (phenol/aniline) monomer (m1). The thermal properties of the different Bz

monomers are in Figure III - 8.

Figure III - 8. Chemical structure and thermal properties of Bz monomers containing carboxylic

groups.158

As it can be seen in Table III - 2, small amounts of monocarboxylic monomer induced a reduction

of about 20 to 30 °C of the polymerization temperature which was even more important when

the amount of carboxylic-containing co-monomer increased. For over 25 % of co-monomer

amount, the polymerization temperatures were even lower than for m2 or m3 alone. In

comparison, mixtures with dicarboxylic monomer m4 were reported to have a stronger catalytic

effect. Indeed, with 5 % of m4, the temperature of copolymerization with m1 was decreased by

50 °C. When comparing the Tg of the copolymer PBz materials, it could be observed that materials

obtained from carboxylic-containing Bz monomers tended to have higher Tgs than m1 based PBz

materials. These results were most probably due to higher crosslinking due to hydrogen bonding

with increasing content of cardboxylic acid functions.

93

Co-monomer % co-monomer Polymerization

temperature (°C) Tg (°C)

Reference :

m1 alone - 262 111

m1 + m2 5 238 121

m1 + m2 50 178 107

m1 + m3 5 232 120

m1 + m3 50 187 146

m1 + m4 5 215 128

m1 + m4 50 192 158

Table III - 2. Thermal properties Bz materials from reaction between m1 and carboxylic-

containing Bz co-monomers m2, m3, and m4. 158

1.1.5 Focus on di-benzoxazine monomers

Di-functional Bz monomers are favoured for the elaboration of high performance PBz materials.

They are divided in two classes, depending on whether they are prepared from a di-phenol (Class

A) or a diamine (Class B). These two classes are schematized in Figure III - 9.

Figure III - 9. Chemical structures of Class A and Class B di-Bz monomers.

The structure-to-properties relationship is similar for Class A and Class B di-Bzs. The rigidity or

the electronic state of the bridging group has a similar impact. Nevertheless, class B di-Bz

monomers, i.e. phenols bridged with a diamine, are of major interest owing to their versatile

synthesis and the numerous mono-phenolic and diamine reagents available. Nevertheless, the

nature of the diamine bridging group is strongly affecting the synthesis conditions and the

thermal properties of Bz monomers and corresponding PBz resins.159-161 162-164 Furthermore, the

nature of the substitution of the phenolic compound drives particular functionality of the Bz

monomers,159, 165-167 such as functional groups promoting the thermal activation of the ROP or

increasing the crosslinking density of the resulting PBz materials.

In the coming paragraphs, we will only focus on the state-of-the art on Class B di-Bzs as they are

the main focus of the work presented in this chapter. For more details, a full description is given

in [Pierre Verge, Laura Puchot, Cédric Vancaeyzeele, Frédéric Vidal, Youssef Habibi, "Symmetric vs

94

asymmetric di-Bz monomer design: structure-to-properties relationship" in "Advanced and

Emerging Polybenzoxazine Science and Technology," Ishida, H.; Froimowicz, P. Eds. Elsevier,

Amsterdam (2016).]

1.2 Synthesis of Class B benzoxazines

The synthesis of class B di-Bz monomers is determined by the nature and origin of each reagent

while the synthesis conditions and yields are strongly affected by the electron donating and

withdrawing effects as well as by the length of the diamine bridging group (Figure III - 10).

Figure III - 10. Chemical structure of Class B di-Bz monomer.

1.2.1 Electron donating and withdrawing effect

The nature of the bridging group represents one of the main factors affecting the ring-closing

reaction of the Bz oxazine rings (Figure III - 1). The influence of electron donating or withdrawing

effects of different bisphenol bridging groups on the Bz ring closure were previously

investigated.168 It was evidenced that the electron donating effect of bridging groups such as –

CH2 or a single bond promotes the formation of the Bz oxazine ring. On the contrary, the

withdrawing effect of bridging groups such as –CO or –SO2 stabilizes the mesomeric form of the

phenolic groups, and thus decreases the capacity of bisphenol to close the oxazine ring. Similarly,

the electronic effect of the diamine bridging group is also affecting the oxazine ring synthesis.

Indeed, the basicity of the primary amines is an important factor for the Bz monomer synthesis.169

Hence, an electron withdrawing effect of the diamine bridging group will tend to lower the amino

group basicity, impeding the Bz oxazine ring closure. On the contrary, electron donating effects

of the diamine bridging group will enhance the basicity of the primary amino groups, promoting

the Bz oxazine ring formation.

1.2.2 Flexibility of the bridging diamine

The flexibility of aliphatic diamines is also impacting the reaction conditions of the monomers

synthesis. The effect of the chain length of aliphatic diamines as bridging groups was

95

investigated.162 The reaction times of the Bz monomer synthesis with increasing diamine chain

length, from short and relatively rigid ethylenediamine to long and relatively flexible 1,12-

diaminooctane, are listed in Table III - 3.

Monomer Diamine Reaction Time (h)

P-ad2 H2N-(CH2)2-NH2

Ethylene diamine 1.5


1,4-diaminobutane 4


1,6-hexane diamine 8


1,8-diaminooctane 10


1,12-diaminododecane 12

Table III - 3. Reaction times of synthesis of Bz monomers in CHCl3 at reflux with increasing

diamine chain length.162

It was evidenced that a short length diamine allowed a faster and easier monomer formation than

a long chain diamine.162 As it can be seen in Table III - 3, the reaction times were shifting from

1.5 h to 12 h while increasing the diamine chain length from 2 to 12 carbons. Low reaction times

are thus favoured by short length diamine bridging groups such as ethylenediamine.

1.3 Thermal properties of Class B di-Bz monomers and PBz resins

As related by numerous studies, the flexibility and chain length of the diamine bridging groups

are largely determining the thermal properties of the di-Bz monomers and their corresponding

PBz materials.

1.3.1 Flexibility and chain length of the bridging diamine

As PBz resins are mainly intended for high performance applications, aromatic diamines that

stand as rigid bridge have been widely used for the design of di-functional Bz monomers,

hereafter known as aromatic-di-Bz. These rigid bridging groups, inspired from the development

of epoxy-based thermoset materials, are largely preferred for the synthesis of high glass

transition temperature (Tg) materials. The thermal properties of model aromatic-di-Bz

monomers, synthetized from aromatic diamines and phenols, and those of their corresponding

PBz materials are listed in Table III - 4.

96

Bz monomer Tm

(°C)

Tp

(°C)

Tg

(°C) Ref.

1,4-phenylenediamine (pd)

- - 260 170

N,N diaminodiphenylmethane (ddm)

123 244 208 160

(4-aminophenyl)ether (dde)

- - 194 170

4,4’-diamino diphenyl sulfone (dds)

209 261 184 160

(4-(4-aminophenoxy)phenyl)ether (44appe)

164 239 172 160

2,2-bis(4-(4-aminophenoxy)naphthalene (ndpa)

152 249 170 160

Table III - 4. Melting point (Tm) and polymerization temperature (Tp) of model aromatic-di-Bz

monomers and Tg of their corresponding aromatic-PBz materials.

Materials with high Tg typically ranging from 170 °C to 260 °C were obtained with aromatic

diamines as bridging groups. Higher flexibility of the aromatic diamine backbone, for example in

the case of 44appe or ndpa, induced a lower Tg, 172 °C and 170 °C respectively, than for Bz with

more rigid aromatic diamine such as 1,4-phenylenediamine (Tg = 260 °C). However, the relatively

high melting temperatures of aromatic-di-Bz monomers (above 120 °C) complicate the materials

processing (molding and shaping), due to the short processing windows Tproc, defined as the

difference between the monomer melting temperature (Tm) and its polymerization temperature

(Tp).

97

The brittle nature of aromatic PBz materials has led researchers to consider aliphatic diamines

as flexible bridging group to design Bz monomers, hereafter known as aliphatic-di-Bz. The

thermal properties of model aliphatic-di-Bz monomers, synthetized from various chain length

linear diamines and phenol, and their corresponding aliphatic-PBz materials are listed in Table

III - 5.

Bz monomer Tm (°C) Tp (°C) Tg (°C) Ref.

Ethylene diamine

112 185 179 162

1,4-diaminobutane

94 225 169 162

1,6-hexane diamine

83 225 171 162

1,8-diaminooctane

73 236 137 162

1,12-diaminododecane

49 241 105 162

Table III - 5. Thermal properties of aliphatic- di-Bz monomers, synthetized from various chain

length linear diamines and phenol, and Tg of their corresponding aliphatic-PBz materials.

The chain length of flexible linear diamine bridging groups is an essential parameter affecting the

thermal properties of the di-Bz monomers and their related PBz materials. The melting

temperatures of aliphatic Bz monomers were found to be significantly lower than those of

aromatic-di-Bz monomers (< 155 °C), while their polymerization temperatures remained in the

usual temperature range of 200-220 °C. Moreover, the melting temperatures of the aliphatic Bz

monomers were considerably decreased, from 112 °C to 49 °C, with increasing the diamine

bridging group chain length. Thus, the processing windows Tproc of aliphatic di-Bz monomers

were wider than for aromatic-di-Bz, from 73 °C to 192 °C with increasing the diamine chain

length. Furthermore, the glass transition temperatures (Tg) also decreased proportionally from

179 °C to 105 °C with increasing the diamine chain length.162

98

In conclusion, the synthesis of aromatic-di-Bz monomers yielded to compounds with relatively

high melting temperatures, and to aromatic PBz with high Tg. On the contrary, flexible bridging

groups (aliphatic diamines) allowed the synthesis of low melting temperature aliphatic-di-Bz

monomers, with a wide processing window. Nevertheless, the higher flexibility of the aliphatic

bridging group impedes the Tg of the materials, underlining the difficulty to find a compromise

for the design of high performance materials with moderate processing conditions.

1.3.2 Additional functional groups

The introduction of some functional groups has been tentatively considered to promote lower

thermal activation or to improve the properties of the resultant PBz materials.

The effect of the allyl group of o-allylphenol on Bz monomers prepared with various diamines

was studied.159, 166, 165 However, despite a lowering of the polymerization activation temperature,

the presence of the allyl group on the phenolic ortho position hampered the polymerization

process of the benzoxazine, resulting in lowering the crosslinking density of the networks.

Maleimide functional groups, were shown to enhance the PBz materials thermal properties.167 A

set of di-Bz monomers was synthetized by bridging phenyl maleimides with various diamines

using xylene as high boiling point solvent (Figure III - 11). The ring-opening polymerization of

the phenyl maleimide-based Bz monomers, as well as the addition-polymerization of the

maleimide groups occurred in the same temperature range of traditional Bz monomers (Tp ~ 200

°C - 220 °C), while the resulting PBz materials exhibited high Tg (c.a. 300 °C) and excellent thermal

stability (T5% > 370 °C).

Figure III - 11. Synthesis of di-Bz monomers bearing maleimide functional groups. 167

In summary, class B di-Bz monomers are considered as the most appropriate and versatile

structures for the synthesis of novel high performance PBz materials. The choice of the diamine

99

strongly affects the synthesis conditions, yields, thermal properties and polymerization kinetics

of class B di-Bz monomers and of their corresponding PBz materials. First of all, a moderate/wide

processing window is important for the easy elaboration of PBz materials. As aromatic-di-Bz

monomers were characterized by high melting temperatures and narrow processing windows,

the use of an aliphatic diamine should be preferred for the synthesis of di-Bz monomers easier to

process due to their wide processing windows. Furthermore, even though the melting

temperature of Bz monomers decreased with increasing the aliphatic diamine chain length, their

Tg was clearly shifted to lower temperatures, lowering the thermo-mechanical properties of the

resulting PBz materials. In addition, the synthesis of Bz monomers with long aliphatic chains was

reported to be distinctly more difficult. As a result, short aliphatic diamine bridging groups, such

as ethylene diamine, should be preferred for the synthesis of di-Bz monomers displaying

moderate processing windows therefore resulting in high crosslinked PBz materials with good

thermal and mechanical properties.

1.4 Bio-based benzoxazine: State of the art

With the growing trend to produce environmentally-friendly and high performance materials

derived from renewable resources, the use of bio-based phenolic derivatives for the synthesis of

Bz monomers is considered as a viable alternative to petroleum-based phenolic counterparts. A

broad screening of various mono- or di-functional Bz monomers from naturally occurring

phenolic compounds, and their resulting materials have been reported during the last years,

attesting the clear trend of promoting the use of renewable bio-resourced reagents for the

development of competitive bio-based thermosets (Figure III - 12).

100

Figure III - 12. Example of naturally occurring phenolic derivatives used for the synthesis of

bio-based Bz monomers.

1.4.1 Vanillin

Vanillin is a phenolic compound with an ortho methoxy group and a para formyl group,

historically produced through extraction from vanilla seedpod but stems industrially mostly from

the processing of lignin.3, 171 Due to the high abundance of sustainable lignin resources,172, 173

vanillin appears as a promising substitute to oil-derived phenolic compounds or polymer

building-blocks.174-178 Its use as a precursor for the synthesis of bio-based Bz monomers was

recently studied.179, 180

The formyl group contained in the vanillin compound is of great interest for the synthesis of bio-

based Bz monomers. Indeed, with the appropriate stoichiometric amount of reagents and through

a convenient order of their introduction and reaction, the aldehyde function is not consumed

during the synthesis. This function is thus considered as an additional reactive group on the Bz

monomer, able to further react with other chemical compounds or to increase the material

crosslinking density.

The chemical structures as well as the thermal properties of vanillin-based Bz monomers and

their corresponding materials, reported in the literature, are summarized in Table III - 6.

101

Bz monomer Tm

(°C)

Tp

(°C)

Tg

(°C)

T5%

(°C) Ref.

1)

Vanillin/Aniline

83 231 - 347 179

2)

Vanillin/Furfurylamine

125 205 270 351 180

3)

Vanillin/Ethylene diamine

205 213 - 283 181

4)

Vanillin/4,4’-diamino diphenyl sulfone (dds)

229 277 255 339 181

5)

Vanillin/N,N diaminodiphenylmethane (ddm)

177 234 231 352 181

102

6)

Vanillin/ (4-aminophenyl)ether (dde)

145 234 227 322 181

7)

Vanillin/2,2-bis(4-(4-aminophenoxy)naphthalene

(ndpa)

- 228 202 488 181

Table III - 6. Thermal properties of vanillin-based Bz monomers, synthetized from mono-

functional amines or diamines, and Tg and T5% of their corresponding PBz materials.

It has been shown that the presence of the aldehyde group on vanillin has an immediate effect on

the thermal properties of the Bz monomer. Indeed, the presence of the formyl group on the

vanillin compound induces the formation of inter- and intra-molecular H bonds. Consequently, in

comparison to classical phenol-aniline Bz monomer, the melting temperature of vanillin-aniline

Bz monomer (Table III - 6, line 1) increased from 61 °C to 83 °C, whereas its polymerization

temperature decreased from 263 °C to 231 °C.179 The effect of inter- and intra-molecular H

bonding is further highlighted by the high melting temperatures of vanillin-based di-Bz

monomers. Indeed, the melting temperatures of the monomer reported in Table III – 6 were not

found to be lower than 145 °C (dde, Table III – 6, line 6), reaching even 229 °C for the di-Bz with

DDS as diamine (Table III – 6, line 4). These high melting temperatures, really close to the

polymerization temperatures are impeding the processing of these monomers (melting and

shaping). Nevertheless, vanillin-based Bz monomers led remarkably to cross-linked materials in

spite of substituted phenolic ortho and para positions, impeding the polymerization. It turns out

that the participation of the aldehyde group in the ring opening polymerization of the Bz

monomers has been previously reported.182 However, it was shown that the additional

crosslinking reactions, due to the presence of an aldehyde group within a Bz monomer, occur

mainly at the ortho position of the phenolic compound (Figure III - 13).

103

Figure III - 13. Schematization of the participation of the aldehyde group in the ring opening

polymerization of the para hydroxyl benzaldehyde Bz monomers.182

As the vanillin ortho position is blocked by a methoxy group, it can be assumed that the additional

crosslinking of vanillin-based Bz monomers is mainly caused by the decarboxylation of the formyl

group (Figure III - 14). Furthermore, some residual formyl groups, which did not undergo

decarboxylation, are forming inter-molecular H-bonding, further increasing the PBz crosslinking

density. Finally, the presence of the residual formyl groups is catalysing the Bz monomers ROP.182

181

Figure III - 14. Crosslinking of vanillin-based di-Bz monomers.181

In consequence, due to the presence of the aldehyde functions and thus to the formation of inter-

and intra-molecular H bonds, the vanillin-based materials were shown to display very high Tgs.

Indeed, vanillin-based di-Bz monomers resulted in PBz networks with Tg values reaching 255 °C

(DDS, Table III – 6, line 4). Nevertheless, di-vanillin Bz monomers are suffering from an evident

drawback: their short processing windows. Indeed, melting temperatures of di-vanillin Bz

monomers are too close from their polymerization temperatures, hindering their processing

(molding and shaping).181

104

1.4.2 Guaïacol

Guaïacol is another lignin-derivative phenolic compound, also studied as precursor for the design

of bio-based benzoxazine monomers.

Up to now, to the best of our knowledge, only mono-functional Bz monomers from guaïacol were

reported in the literature. The effect of two different bio-based primary amines on the thermal

properties of the monomer and corresponding PBz material were studied (Table III - 7). DSC

measurements revealed a Tg of 82 °C for a material obtained from the reaction between guaïacol

and stearylamine (Table III – 7, line 1). When furfurylamine was used for the synthesis of

guaïacol-based Bz monomer, an increase of the Tg to = 148 °C was reported (Table III – 7, line 2).

The authors did not give any information about the monomers melting points: the PBz materials

were shaped by solution casting of the monomers dissolved in acetone.

Bz monomer Tm (°C) Tp (°C) Tg (°C) T5% (°C) Ref.

1)

Guaïacol/Stearylamine

- - 82 329 183

2)

Guaïacol/Furfurylamine

- 240 148 352 183

Table III - 7. Thermal properties of guaïacol-based Bz monomers, synthetized from mono-


1.4.3 Lignin-derivatives

Among the lignin derivatives, coumaric (CA) and ferulic (FA) acids are present in relatively large

quantity in various plants as main components of lignocellulose.184 In addition, phloretic acid (PA)

is a phenolic compound obtained by hydrogenation of p-coumaric acid (Figure III - 15).

105

Figure III - 15. Chemical structure of lignin-derivative compounds: coumaric acid (CA), ferulic

acid (FE), and phloretic acid (PA).

These lignin-derivative compounds, as well as their methylated equivalents (CAM, FAM and PAM

respectively), were studied as precursor of mono-functional Bz monomers (Table III - 8). Bz

monomers with relatively high melting temperatures were obtained. Polymerization

temperatures of the Bz monomers were strongly affected by the carboxylic acid function. Indeed,

the carboxylic acid function acts as a polymerization catalyst, lowering the polymerization

temperatures compared to Bz with methylated functions. Thus, similarly to di-vanillin Bz

monomers, processing windows of Bz monomers with carboxylic acid function were low, due to

high melting temperatures (Tm = 117 °C and 121 °C for CA-Bz, FA-Bz) and low polymerization

temperatures (Tp = 137 °C and 130 °C respectively). The use of the methylated coumaric and

ferulic compounds allowed an increase of the processing window by increasing the

polymerization temperatures (processing windows = 107 °C and 37 °C respectively).

Furthermore, low thermal stability was reported for CA-Bz and FA-Bz, as well as for their

methylated derivatives CAM-Bz and FAM-Bz. Indeed, except for phloretic acid and methylated

phloretic acid based Bz monomers (PA-Bz and PAM-Bz), the polymerization proceeded with

partial decomposition, probably due to the presence of the conjugated double bond. This

phenomenon also impeded the preparation of suitable materials.

Bz monomer Tm (°C) Tp (°C) Tg (°C) T5% (°C) Ref.

1)

CA/aniline

117 137 119 220 184

106

2)

CAM/aniline

109 216 154 280 184

3)

FA/aniline

121 130 120 200 184

4)

FAM/aniline

166 203 135 135 184

5)

PA/aniline

122 212 130 130 184

6)

PAM/aniline

156 197 115 143 184

Table III - 8. Thermal properties of lignin-derivative-based Bz monomers, synthetized from

mono-functional amines or diamines, and Tg and T5% of their corresponding PBz materials.

107

1.4.4 Eugenol

Eugenol, through its availability and low cost, has also attracted attention for the synthesis of bio-

based Bz monomers. Eugenol is the main component (72 to 90 %) in the essential oil obtained

from cloves. It can also be extracted from other essential oils such as nutmeg, cinnamon, basil or

bay leaf oils. Eugenol chemical structure is a di-substituted phenolic compound by a methoxy and

an allyl group at ortho and para positions respectively. Consequently, due to blocked ortho and

para positions, only the low reactive meta positions are available, impeding the formation of a

cross-linked eugenol-based network (Figure III – 16).

Figure III - 16. Available positions for ring opening polymerization of eugenol-based Bz

monomer.

Furthermore, despite the allyl functional group on eugenol compound in para position, no

enhancement of the crosslinking density through homopolymerization of the resulting materials

was reported. Indeed, as the allyl group is attached to an aromatic structure, any formed radical

is stabilized by mesomeric effect, preventing free radical polymerization.185, 186 However, the

crosslinked materials from eugenol-based Bz monomers was obtained by using the allyl group as

a reactive function, and copolymerizing them with bismaleimides (Figure III - 17).187

Figure III - 17. Elaboration of crosslinked materials from eugenol-based Bz monomers by

copolymerization between allyl group and bismaleimides.187

108

As it can be observed in Table III - 9 m-Bz monomers from eugenol displayed large processing

windows but the Tg of the resulting materials, obtained from DSC, were relatively low (Tg = 101

°C and 148 °C for eugenol Bz monomers with stearylamine and furfurylamine respectively)

(Table III – 9, line 1 and 2).186 Similarly to di-Bz monomers from other naturally occurring

phenolic compounds, di-Bz monomers from eugenol and various aromatic diamines were all

displaying fairly high Tm > 90 °C, hampering also the elaboration of eugenol-based PBz

materials.188

Bz monomer Tm

(°C)

Tp

(°C)

Tg

(°C)

T5%

(°C) Ref.

1)

Eugenol/Stearylamine

49 218 101 313 186

2)

Eugenol/Furfurylamine

74 198 148 361 186

3)

Eugenol/ (4-(4-aminophenoxy)phenyl)ether

(44appe)

90 250 - 260 188

4)

Eugenol/1,4(bis(4’-aminophenoxy)phenyl sulfone)

(14apps)

100 250 - 275 188

5)

Eugenol/ (4-aminophenyl)ether (dde)

140 225 - 240 188

109

6)

Eugenol/4,4’-diamino diphenyl sulfone (dds)

130 255 - 295 188

7)

Eugenol/1,4-phenylene diamine

150 250 - 225 187

Table III - 9. Thermal properties of eugenol-based Bz monomers, synthetized from mono-


1.4.5 Coumarin

Coumarin was also studied as bio-resourced reagent for the synthesis of bio-based Bz monomers.

The specific coumarin compounds bearing a hydroxyl group in position 7 are of particular

interest for the synthesis of bio-based Bz monomers. Several studies reported the synthesis of Bz

coumarin monomers either from umbeliferone (Figure III - 18a) or from 4-methylumbeliferone

(Figure III - 18b) coumarin compounds. Their properties are reported in Table III - 10.

Figure III - 18. Chemical structures of a) umbeliferone and b) 4-methylumbeliferone coumarin

compounds.

Even though the corresponding PBz materials exhibited high glass transition temperatures (Tg

around 185 °C), the processing of these materials is impeded by high melting temperatures, above

140 °C. However, coumarin-based PBz materials were shown to have relatively high degradation

temperatures, above 300 °C. Consequently, coumarin compounds are considered as competitive

bio-based reagents for the synthesis of high performance PBz materials, comparable to

traditional petroleum-based ones.

110

Bz monomer Tm

(°C)

Tp

(°C)

Tg

(°C)

T5%

(°C) Ref.

1)

Umbeliferone/aniline

147 220 183 327 189

2)

4-methylumbeliferone/aniline

153 232 189 312 190

3)

4-methylumbeliferone/p-toluidine

163 229 - 304 191

Table III - 10. Thermal properties of coumarin-based Bz monomers, synthetized from mono-


1.4.6 Cardanol

Growing interest has arisen towards the synthesis of Bz monomers stemming from Cardanol.

Indeed, the particular chemical structure of cardanol appears as a clear asset for the synthesis of

PBz materials. Cardanol displays a similar reactivity as phenol through the presence of the

hydroxyl group. Furthermore, the long alkyl chain in meta position imparts hydrophobicity and

flexibility, through internal plasticization of the alkyl chain, to the usually brittle PBz materials.

Moreover, the ortho and para positions of cardanol are available for the synthesis of Bz monomers

and their polymerisation respectively.

The chemical structures, as well as the thermal properties of cardanol-based Bz monomers and

their corresponding materials are resumed in Table III - 11.

111

BZ monomer Tm

(°C)

Tp

(°C)

Tg

(°C)

T 5%

(°C) Ref.

1)

Di-cardanol /Ammonia

- 243 36 - 155

2)

Cardanol/Aniline

- 263

58

355

192

3)

4)Cardanol/Stearylamine

- 276

52.8

- 193

4)

Cardanol/Benzylamine

- 263

54

- 193

5)

Cardanol/Furfurylamine

- 271 100 - 194

6)

Cardanol/4,4’-diamino diphenyl sulfone (dds)

- 251 - 299 195

196

7)

Cardanol/ (4-(4-aminophenoxy)phenyl)ether

(44appe)

114 233 - 348 195

196

8)

70 267 - 354 195

196

112

Cardanol/bis-(3-(4-aminophenoxy)phenyl)ether (34

appe)

9)

Cardanol/2,2-bis(4-(4-

aminophenoxy)phenyl)propane (appp)

- 263 - 323 195

196

Table III - 11. Thermal properties of cardanol-based Bz monomers, synthetized from mono-


Almost all of the reported cardanol-based Bz monomers synthesized with short amines did not

display a melting endotherm in response to DSC analysis, as the monomers were in a waxy

amorphous state at ambient temperature. This phenomenon could be attributed to the steric

hindrance generated by the C15 alkyl side chain of cardanol that prevent crystallization.

However, it can be noticed that high melting temperatures were observed for cardanol-based di-

Bz monomers with rigid aromatic diamine as bridging groups, such as bis-(3-(4-

aminophenoxy)phenyl)ether or (4-(4-aminophenoxy)phenyl)ether (Tm = 70 °C and 114 °C

respectively). (Table III – 11, lines 8 and 7)

Generally Bz ring opening polymerization temperatures are ranging from 160 °C to 220 °C,126

while with cardanol, the polymerization temperature were reported to be higher (between 230

°C and 260 °C). The higher polymerization temperatures were certainly due to the steric

hindrance brought by the side chain, impeding the polymerization upon curing. Hence, the

molding and shaping of cardanol-based Bz monomers is facilitated by a wide processing window,

but their overall processing is strongly hampered by high polymerization temperatures (< 230

°C).

Furthermore, it is noteworthy that the thermo-mechanical properties of these PBz materials were

almost never characterized by DMA analysis, as it is very difficult to obtain self-supported

materials due to the steric hindrance of alkyl side chain, yielding to low molecular weight

polymer. Thus, the glass transition temperatures of short amine based PBz reported in the

literature were obtained from DSC analysis (Table III – 11, lines 6 to 9). They are found to be

very low, from 36 °C to 60 °C.

Ambrozic and al. proposed to increase the functionality of the Bz monomer through the reaction

between cardanol and furfurylamine (Table III – 11, line 5).194 The furanic ring of furfurylamine

is highly reactive and promotes thus an increase of the crosslinking density.197 Indeed, when

comparing cardanol-based mono-functional Bz monomers to other amine derivatives, such as

aniline or benzylamine (Tg = 58 °C and 52.8 °C respectively) (Table III – 11, line 2 and 4,

113

respectively) for example, a distinct shift of the Tg to higher temperatures (Tg = 100 °C), was

observed for the furfurylamine-based PBz material. Very interestingly, the use of furfurylamine

accessed to the formation of a self-supported material, which could be analysed by DMA.

Consequently, cardanol-based Bz monomers displayed wide processing windows owing to their

low melting temperatures due to the steric hindrance brought by the C15 alkyl chain. However,

the low crosslinking density and Tg of the corresponding PBz materials, as well as the high

polymerization temperatures, are major drawbacks for the elaboration of high performance

thermosets from cardanol with good thermo-mechanical properties.

1.4.7 Urushiol

Urushiol is another naturally occurring phenolic compound, extracted from lacquer trees. Its

chemical structure is very close to those of cardanol as it is a 3-substituted catechol derivative

with a C15 alkyl chain in meta position. Like for the cardanol compound, the unsaturation degrees

of the alkyl chain, from unsaturated to tri-saturated, and their abundances are varying (Figure

III - 19).

Figure III - 19. Chemical structure of urushiol.

One benzoxazine moiety can be synthetized on the available hydroxyl ortho position of urushiol.

Unlike cardanol, urushiol does not present a free ortho position for the polymerization.

Nevertheless, free para and meta positions are available for the urushiol-based Bz monomers

polymerization (Figure III - 20).

114

Figure III - 20. Available positions for ring opening polymerization of urushiol-based Bz

monomer.

The properties of the Bz monomers synthetized from urushiol are resumed in Table III - 12.

BZ monomer Tm

(°C)

Tp

(°C)

Tg

(°C)

T5%

(°C) Ref.

1)

Urushiol/Aniline

/ 211 140 325 198

2)

Urushiol/N,N diaminodiphenylmethane (ddm)

110 212 135 350 199

Table III - 12. Thermal properties of urushiol-based Bz monomers, synthetized from amines or

diamines, and Tg and T5% of their corresponding PBz materials.

A liquid Bz monomer (Tm < Tamb) was obtained through reaction with paraformaldehyde and

aniline with a polymerization temperature of Tp = 211 °C (Table III – 12, line 1).198 Similarly to

cardanol, urushiol appears as a good precursor for the synthesis of low melting temperature Bz

monomers. In spite of the presence of the long alkyl chain, the corresponding urushiol-based PBz

materials exhibited high glass transition temperatures of 135 °C (urushiol/aniline) and 140 °C

(urushiol/ddm) (Table III – 12, line 1 and 2, respectively) while cardanol/aniline PBz exhibited

a Tg of 58 °C (Chapter III - 1.4.6). Urushiol-based Bz monomers are thus promising for the

development of tough bio-based PBz materials with good thermo-mechanical properties.

In conclusion, the use of naturally occurring phenolic compounds for the synthesis of Bz

monomers allows the lowering of the carbon footprint, and enables the introduction of some

115

additional and/or functional groups within the Bz monomers. Alike petroleum-based Bz

monomers, the nature of the diamine bridging group strongly affects the bio-based Bz monomers

properties and their polymers. Short aliphatic diamine bridging groups, such as ethylene diamine,

should as well be preferred for the synthesis of bio-based Bz monomers. Indeed, the use of short

aliphatic diamines promotes expected moderate processing windows, while resulting in high

crosslinked PBz materials with good thermal and mechanical properties.

Nevertheless, most of the Bz monomers synthetized from bio-based phenolic compounds are

suffering from several disadvantages, either for the synthesis of the Bz monomer, or for the

elaboration and/or for the properties of the final materials. Natural occurring phenolic

compounds such as lignin-derivatives or coumarin compounds lead to highly crosslinked PBz

materials with good thermo-mechanical properties, whereas their processing is hindered by

narrow processing windows. On the contrary, bio-based Bz monomers synthetized from phenolic

compounds like cardanol, urushiol, or eugenol display large processing windows, but low

crosslinking density and low Tg. As the overall performance of PBz is strongly affected by oxazine

ring substitutions, drawbacks of some bio-based phenolic compounds could be offset by the

assets of others to yield Bz monomers with large processing windows and corresponding high

performance PBz materials.

1.5 Asymmetric benzoxazine monomers

1.5.1 State of the art

Bz monomer substitutions can modify their melting temperatures and impact the crosslink

density of the resulting PBz, allowing thus the control of their properties. Additional

functionalities could also be imparted to the monomer by appropriate chemical derivatization of

the Bz monomers as Ishida reported for a new benzoxazine-based surfactants.200 Nevertheless,

due to the symmetric nature of the monomer, the functionalities that could be added are limited

by the chosen phenolic derivative.

An elegant approach of adding different functionalities on Bz monomers consists of designing

asymmetric di-Bz monomers, using for example a diamine as bridging group between two

phenolic derivatives exhibiting each a particular functionality. Different synthesis strategies were

developed in order to access asymmetric di-Bz monomers.

The first example dealing with the synthesis of an asymmetric di-Bz monomer was reported

recently (2013).201 Aminophenol was reacted with the aldehyde group of a hydrobenzaldehyde

compound to form an imine linkage between the two phenolic compounds (Figure III - 21). The

imine was reduced by using NaBH4 and the oxazine rings were further formed using

116

formaldehyde. The second oxazine ring was obtained by ring-closure reaction using a mono-

amine, either butylamine (u-butyl-Bz) or hexylamine (u-hexyl-Bz). Both asymmetric Bz, u-hexyl-

Bz and u-butyl-Bz, have shown similar processing properties (Tp in the range of 210 °C - 240 °C)

with very large processing windows as no melting endotherm was observed on the DSC

thermograms.

Figure III - 21. Synthesis di-Bz asymmetric monomer by reaction between aminophenol and

hydrobenzaldehyde and butylamine (u-butyl-Bz) or hexylamine (u-hexyl-Bz).201

Another possibility is to start from a mixture of symmetric and asymmetric Bz monomers. They

were prepared from phenol, eugenol and 1,4-phenylenediamine by Dubois et al.202 (Figure III -

22). The three Bz monomers were synthetized ‘in-situ’ without a real control of the occurring

reactions. The introduction of an eugenol part within the molecule allowed a solvent-free

synthesis while the phenol part was used to enhance the crosslink density of the resulting

material. The Tg increased from 120 °C to 220 °C with the (phenol : eugenol) ratio ranging from

(1 : 1) to (1.8 : 0.2).

117

Figure III - 22. Synthesis of blends of di-eugenol, di-cardanol and asymmetric eugenol/cardanol

di Bz monomers. 202

Motivated by these approaches, we proposed to design an asymmetric bio-based di-Bz monomer

based on vanillin and cardanol.203 Indeed, symmetric di-Bz monomer synthetized from vanillin

and ethylenediamine (EDA) suffers from a major drawback: its melting temperature (Tm = 218

°C) is too close to its polymerization temperature (Tp = 225 °C) making its processing (molding

and shaping) very challenging.181 To tackle this issue, we aimed in the present work to prepare

bio-phenol based di-Bzs exhibiting large difference between Tm and Tp which can be achievable

by the design of asymmetric di-Bzs with vanillin moiety and another phenolic compound yielding

Bz with low melting temperatures. From previous studies,196 it was expected that cardanol could

be a good candidate to design asymmetric Bz monomers with vanillin to obtain low melting

temperature Bzs and thus expand the processing window. Indeed, the cardanol alkyl side chain

provides better processability and flexibility to the material through internal plasticization.

Furthermore, the presence of the alkyl chain causes steric hindrance, lowering thus the

compound reactivity. Indeed, it was observed that the synthesis of di-vanillin Bz monomer was

straightforward and fast whilst the synthesis of di-cardanol was rather slow. The steric hindrance

brought by the cardanol side chain impeded also its polymerization upon curing, as indicated by

the low enthalpy recorded in DSC for the di-cardanol Bz monomer (32.5 J/g versus 121 J/g for di-

vanillin) as well as the formation of a loosely crosslinked network. Indeed, the steric hindrance

brought by the alkyl chain lead to material with low molecular weight, as attested by the difficulty

to obtain material from di-cardanol Bz that does not creep above Tg.


The detailed experimental conditions are reported in annex p 181.

118

2.1 Symmetric benzoxazine monomers synthesis and characterization

2.1.1 Symmetric Bz monomer synthesis

In a first time, symmetric benzoxazine monomers from phenol, vanillin or cardanol (coined

hereafter di-phenol, di-vanillin and di-cardanol) were synthetized by reacting together phenol or

vanillin or cardanol, paraformaldehyde and ethylene diamine (EDA) is stoichiometric ratio 2:4:1

(Figure III - 23).

Figure III - 23. Synthesis of symmetric Bz monomers from various phenolic compounds like

phenol, vanillin or cardanol.

The structural features of the obtained products were characterized by 1H NMR and HRMS.


- Di-phenol benzoxazine monomer

The 1H NMR spectrum corresponding to the di-phenol Bz monomer is depicted in Figure III - 24.

119

Figure III - 24. 1H NMR spectrum (in CDCl3) of di-phenol benzoxazine monomer.

The 1H NMR spectrum of the reference di-phenol Bz monomer displays the characteristic peaks

of a benzoxazine structure. Indeed, the formation of the Bz was revealed by the presence of peaks

corresponding to the protons from the O-CH2-N and Ar-CH2-N groups. These characteristic groups

were observed in the case of the di-phenol monomer at δ = 4.07 ppm and δ = 4.92 ppm

respectively. Furthermore, the signal integrations were confirming the structure of the di-

benzoxazine from phenol and EDA. The signal of the aromatic protons [1,2,3,4] at δ = 7.15 – 6.78

ppm was taken as integration reference and should integrate for 8 H. Thus, the integrations for

the peaks corresponding to O-CH2-N [6] and Ar-CH2-N [5] were found to integrate for Iexp = 3.73

H and Iexp = 4.02 H respectively as expected (Ith = 4.00 H for each peak). The signal corresponding

to EDA [7] was also observed at δ = 3.02 ppm and Iexp = 4.08 H (Ith = 4.00 H). The 1H NMR analysis

confirmed the expected chemical structure of the di-phenol Bz monomer. The chemical shifts, as

well as their experimental and theoretical integrations are summarized in Table III - 13.

120

Chemical shift


3.02 N-CH2*-CH2

[7] 4.08 H 4.00 H

4.07 Ar-CH2-N

[5] 4.02 H 4.00 H

4.92 O-CH2-N

[6] 3.73 H 4.00H

7.15 – 6.78 H-Ar

[1,2,3,4] Ref 8.00 H 8.00 H

Table III - 13. Assignments of the 1H NMR peaks of the di-phenol benzoxazine monomer and

their theoretical and experimental integrations.

- Di-vanillin benzoxazine monomer

The 1H NMR spectrum corresponding to the di-vanillin monomer is depicted in Figure III - 25.

Figure III - 25. 1H NMR spectrum (in CDCl3) of di-vanillin benzoxazine monomer.

For the di-vanillin Bz monomer, the peak corresponding to the –OCH3 [6] function of vanillin was

chosen as integration reference. In the case of a di-vanillin monomer, this peak should integrate

for 6H. On the di-vanillin 1H NMR spectrum displayed in Figure III - 25, the characteristic peaks

corresponding to the vanillin compound were revealed. The hydrogens from the aldehyde

121

function [7] appeared at δ = 9.81 ppm with Iexp = 2 H (Ith = 2 H). The integration of aromatic proton

of vanillin [1, 2] at δ = 7.13-7.32 ppm further confirmed the presence of two vanillin moieties (Iexp

= 1.99 H and Ith = 2.00 H). Peaks corresponding to EDA [5] were also observed at δ = 3.02 ppm

where Iexp = 3.70 H (Ith = 4 H). Furthermore, characteristic peaks at δ = 4.13 ppm and at δ = 5.08

ppm, which correspond to the Ar-CH2-N [3] and to O-CH2-N [4] protons respectively, indicated

the formation of di-Bz monomer from vanillin. All the expected theoretical integrations as well as

the corresponding experimental integrations for the di-vanillin monomer are reported in Table

III - 14.

Chemical shift


3.02 N-CH2*-CH2

[5] 3.70 H 4.00 H

3.95 O-CH3

[6] Ref 6.00 H 6.00 H

4.13 Ar-CH2-N

[3] 4.01 H 4.00 H

5.08 O-CH2-N

[4] 4.02 H 4.00H

7.13 H-Ar

[1, 2] 1.99 H 2.00 H

7.32 H-Ar

[1, 2] 1.99 H 2.00 H

9.81 (C=O)H2

[7] 2.00 H 2.00 H

Table III - 14. Assignments of the 1H NMR peaks of the di-vanillin benzoxazine monomer and


- Di-cardanol benzoxazine monomer

Similarly, the structure of the di-cardanol Bz monomer was confirmed by the 1H NMR

characterization (Figure III - 26).

In regard to the integration of the NMR signals relative to the cardanol compound, the precise

integration depends obviously on the composition of cardanol and related proportion of different

isomers. The integrations are usually calculated by moderation based on the abundance of

122

unsaturation described in the literature.11, 51, 204-206 These unsaturation abundances can slightly

vary regarding the origin and the processing of raw Cardanol extracted from CNSL. As such the

integration may diverge from sample to other. The unsaturations abundances of the used

cardanol were considered as following: tri-unsaturated (n=3) ~ 41%, di-unsaturated (n=2) ~

23%, mono-saturated (n=1) ~ 34%, saturated (n=0) ~ 3%.11, 50, 204-206 In addition, the difference

of relaxation times between aromatic and aliphatic hydrogen may complicate the accurate

quantification of all protons. Therefore, the peaks related to the aliphatic chain of cardanol were

integrated to the aliphatic hydrogen in β position of the cardanol aromatic ring, which should

integrate for 2H.

Figure III - 26. 1H NMR spectrum (in CDCl3) of di-cardanol benzoxazine monomer.

The characteristic peaks of cardanol were observed, especially the aromatic protons [1, 2, 3] at δ

= 6.60 – 6.88 ppm which integrate each for about 2 H (see Table III - 15) indicating the probable

presence of two cardanol moieties within the monomer. This was further confirmed by the

integration of the following peaks from cardanol , the alkyl chain olefinic CH2 protons [b2, d2, e2,

g2, h2, a2] at δ = 4.96 – 5.88 ppm, the protons in α of the alkyl chain unsaturations [c2, f2, i2] at δ =

1.98 – 2.09 ppm, as well as the CH2 protons in α of the aromatic [o] at δ = 2.49 – 2.57 ppm, the CH2

from the alkyl chain [b1, c1, d1, e1, f1, g1, h1, i1, j, k, l, m, n] at δ = 1.23 – 1.43 ppm and the CH3 of the

alkyl chain [a1] at δ = 0.86 – 0.94 ppm. The CH2 of the alkyl chain comprised between two

unsaturations [c3, f3] were detected at δ = 2.76-2.87 ppm. The experimental and theoretical

integrations of the di-cardanol Bz compound peaks are reported in the Table III - 15. As it can be

observed, the experimental integrations of the peaks corresponding to the cardanol moiety are

123

close to the expected integrations for the di-cardanol Bz monomer containing two cardanol

moieties.

The formation of the benzoxazine structure was verified by the presence of benzoxazine

characteristic peaks at δ = 4.03 ppm and at δ = 4.89 ppm corresponding to Ar-CH2-N [4] and to O-

CH2-N [5] respectively, both peaks integrating as expected for approximately 4.00 H.

Chemical shift


0.86 – 0.94 -CH3

[a1] 4.08 H 3.54 H

1.23 – 1.43

-CH2

[b1, c1, d1, e1, f1, g1,

h1, i1, j, k, l, m, n]

27.58 H 27.12 H

1.54 – 1.64 -CH2 in β from Ar

[n] 4.00 H 4.00 H

1.98 – 2.09 CH2*=CH

[c2, f2, i2] 7.47 H 6.20 H

2.49 – 2.57 CH2-Ar

[o] 4.47 H 4.00 H

2.76 – 2.87 CH2*(=CH)2

[c3, f3] 4.74 H 4.20 H

2.99 N-CH2*-CH2

[6, 7] Ref 4.00 H 4.00 H

4.03 Ar-CH2-N

[4] 3.98 H 4.00 H

4.89 O-CH2-N

[5] 4.00 H 4.00 H

4.96 – 5.88 CH=

[b2, d2, e2, g2, h2, a2] 1.69; 7.55; 0.94 H 1.64; 6.48; 0.82 H

6.60 – 6.90 H-Ar

[1, 2, 3] 2.01; 2.07; 1.93 H 2.00; 2.00; 2.00 H

Table III - 15. Assignments of the 1H NMR peaks of the di-cardanol benzoxazine monomer and


124

*Matrix

2.1.3 Characterization by MALDI-TOF/MS or HRMS

The chemical structure of the di-phenol symmetric Bz monomer were confirmed by MALDI-

TOF/MS characterisation, and by High Resolution Mass Spectrometry (HRMS) characterisation

for the di-vanillin and di-cardanol monomers.

- Di-phenol benzoxazine monomer

The chemical structure of the synthetized reference di-phenol Bz monomer was characterized by

MALDI-TOF/MS. The corresponding spectrum is displayed in Figure III - 27.

Figure III - 27. MALDI-TOF/MS spectrum of di-phenol benzoxazine monomer.

The expected protonated compound [M+H]+ was observed at m/z 297. Nevertheless, ions at m/z

285 and at m/z 283, assigned as [M+H+H2O-CH2O]+ and [M-H+H2O-CH2O]+ resulting from a

reaction during the analysis timeframe were also detected, as expected from mass spectrometry

analyses of Bz monomers. 207, 208 Indeed, di-Bz monomers were found to strongly react during the

timeframe of mass analysis through ion/molecules reactions upon the addition of water and the

subsequent release of formaldehyde from the protonated compound. Since air humidity

encountered during the preparation undoubtedly accounts for this ion/molecule reaction, their

occurrences have not been avoided despite the use of a solvent-free sample preparation.

125

- Di-vanillin benzoxazine monomer

The HRMS spectrum of the di-vanillin Bz monomer is displayed in Figure III - 28.

Figure III - 28. HRMS spectrum of di-vanillin benzoxazine monomer.

The protonated specie of di-vanillin [M+H]+ appeared at m/z 413, confirming the formation of a

di-Bz monomer from vanillin. Likewise for the di-phenol Bz monomer, ions at m/z 401 and at m/z

399, assigned as [M+H+H2O-CH2O]+ and [M-H+H2O-CH2O]+ resulting from a reaction during the

analysis timeframe were also detected as expected.

A zoom of this spectrum region is visible on the Figure III - 29 as well as the theoretical mass

spectrum expected for the di-vanillin compound.

Figure III - 29. HRMS analysis of di-vanillin Bz monomer a) Zoom of the experimental product

peaks b) Theoretical mass of the expected product.

126

As observed in the Figure III - 29, the di-vanillin Bz monomer was detected at m/z 413.1703. The

mass of the di-vanillin Bz monomer is very close to the expected mass of m/z 413.1707,

confirming the chemical structure verified by the previous 1H NMR analysis.

- Di-cardanol benzoxazine monomer

Likewise for the di-vanillin monomer, the expected typical peaks of di-cardanol Bz were present

in the corresponding HRMS spectrum: the compound protonated specie [M+H]+ appeared at m/z

709 as well as at m/z 696 and at m/z 694, assigned as [M+H+H2O-CH2O]+ and [M-H+H2O-CH2O]+

ions of di-cardanol Bz monomer respectively (Figure III - 30).

Figure III - 30. HRMS spectrum of di-cardanol benzoxazine monomer.

A zoom of this spectrum region as well as the theoretical mass spectrum expected for the di-

cardanol Bz monomer is displayed in Figure III - 31.

Figure III - 31. HRMS analysis of di-cardanol Bz monomer a) Zoom of the experimental product


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The experimental mass observed for di-cardanol at m/z 709.5668 is very close to the expected

theoretical mass of m/z 709.5667, confirming the chemical structure of di-cardanol Bz

compound.

Nevertheless, some unexpected additional peaks were observed around m/z 380-400 (Figure III

- 30). In order to verify that these peaks are not impurities but fragments of the original di-

cardanol compound, MS/MS analysis was achieved on the monomer.

As it can be readily observed on the MS/MS spectrum of the di-cardanol Bz monomer (Figure III

- 32), remaining peaks at m/z 401, 383, and 358 were resulting from fragmentation during the

analysis timeframe.

Figure III - 32. MS/MS analysis of di-cardanol Bz monomer.

In conclusion, the synthetized compounds appear to be pure as confirmed by the MALDI/TOF-

MD and HRMS characterizations.

2.1.4 Characterization by DSC and TGA

The thermal behaviour of the symmetric monomers was investigated by DSC and TGA analyses.

For each monomer, the DSC and TGA analyses were carried out at a heating rate of 20 K/min

under nitrogen atmosphere.

- Di-phenol Bz monomer

The DSC and TGA analysis of the di-phenol monomer are displayed in Figure III - 33. The DSC

analysis revealed a moderate processing window of the di-phenol monomer with Tm = 115 °C and

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Tp = 212 °C. The processing of this monomer to a polybenzoxazine material is thus relatively easy.

Furthermore, it can be observed on the TGA analysis that the monomer was able to polymerize

at elevate temperatures, around 210 °C, before undergoing thermal degradation (T5% = 287 °C).

Figure III - 33. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of di-phenol monomer.

- Di-vanillin Bz monomer

As it can be observed on the Figure III - 34, the di-vanillin Bz monomer displayed a relatively

high melting temperature of Tm = 218 °C, barely distinguished from the maximum exothermic

peak temperature of ring-opening reaction occurring at Tp = 225 °C. These close transition

temperatures, impede the monomer processing (molding and shaping), as the monomers

polymerization begins quasi simultaneously with its melting. The high melting temperature of di-

vanillin Bz monomer is probably inducted by the presence of the formyl group on vanillin,

promoting the formation of a stiff crystalline structure brought by intra- and inter-molecular H

bonding network.

In addition, the TGA analysis (Figure III - 34) revealed an early thermal degradation of the

monomer, even before the melting (T5% = 203 °C), further impeding the elaboration of a

polybenzoxazine material from the di-vanillin monomer.

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Figure III - 34. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of di-vanillin Bz monomer.

- Di-cardanol Bz monomer

In contrary to the di-vanillin compound, the di-cardanol Bz monomer exhibited a low melting

temperature of Tm = 44 °C. This result is most probably due to the presence of the C15 alkyl side

chain in meta position. Indeed, cardanol is well-known to provide flexibility to materials through

plasticizing effect. The polymerization temperature was found to be at Tp = 219 °C, within the

expected polymerization temperature range of di-Bz monomers. The di-cardanol Bz monomer

presents thus the advantage of a very large processing window.

Furthermore, when comparing the DSC and TGA analysis (Figure III - 35), it can be observed that

the di-cardanol Bz monomer thermal degradation occured at higher temperature than its ring

opening polymerization temperature. Indeed, T5% = 260 °C whereas Tp = 219 °C, indicating that

the monomer is able to polymerize without early thermal degradation. Moreover, it can be noted

that the thermal degradation temperature for the di-cardanol Bz monomer was much higher than

the degradation temperature of the di-vanillin Bz monomer (T5% = 203 °C).

130

Figure III - 35. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of the di-cardanol

benzoxazine monomer.

2.1.5 Characterization by rheology analysis

Rheology experiments were monitored for each symmetric Bz monomer in order to evaluate their

polymerization reactivity. The polymerization measurements were achieved with a plate-plate

geometry (diameter 25 mm, measure gap 0.5 mm) and recorded at an imposed 1 % deformation

at 1 Hz frequency at 190 °C.

It is worth indicating the unsuccessful monitoring of rheology experiments for di-vanillin Bz due

to the (quasi) simultaneous monomers melting, polymerization and thermal degradation. Indeed,

di-vanillin Bz exhibits a relatively high melting temperature (Tm = 218 °C) barely distinguished

from the maximum exothermic peak temperature of ring-opening reaction occurring at Tp = 225

°C (Figure III - 34). These close transition temperatures, in addition to the early thermal

degradation of the monomer (203 °C), impede its elaboration. Efforts to moderate the reactivity

by adjusting the curing conditions were unsuccessful.

- di-phenol Bz monomer

The rheo-kinetic characterization of the di-phenol Bz monomer upon polymerization is displayed

in Figure III - 36. The di-phenol Bz monomer crosslinking at 190 °C was evidenced by the rapid

increase of the storage and the loss modulus. The recorded gelation time, corresponding to the

crossover point of G’ and G’’, was very short as it is found to be in the range of [4-5] min,

confirming thus the high reactivity of di-phenol Bz monomer.

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Figure III - 36. Isothermal rheology monitoring of di-phenol Bz monomer at 190 °C – empty

markers: storage modulus G’; filled markers: loss modulus G’’.

- di-cardanol Bz monomer

The rheogram, depicted in Figure III - 37, represents the evolution of the storage modulus G’ and

the loss modulus G’’ of the di- cardanol Bz monomer during their polymerization at 190 °C. Full

ploted rheogram is depicted in Annex Figure 2 p 190.

Figure III - 37. Isothermal rheology monitoring of di-cardanol Bz monomer at 190 °C – empty

markers: storage modulus G’; filled markers: loss modulus G’’.

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The behaviour of di-cardanol upon heating is typical to thermosets with a significant increase of

both G’ and G’’, evidencing the starting of the crosslinking at 190 °C. The gelation time, was

observed in the range of [30-31] min highlighting the low reactivity of di-cardanol Bz monomers.

In conclusion, cardanol di-Bz monomer was found to display a large processing window (ΔTproc =

175 °C) due to very low melting temperature (Tm = 44 °C), which makes it an interesting precursor

for easily processable bio-based Bz. Indeed, when comparing to the di-phenol Bz monomer (Tm =

115, ΔTproc = 97 °C), the presence of the cardanol alkyl chain seemed to favorise lower melting

temperatures, probably due to sterical hindrance. However, the steric hindrance brought by this

side chain seemed to impede its polymerization upon curing as indicated by its very long gelation

time [30-31] min at 190 °C recorded in rheology experiments (di-phenol Bz monomer Tgel = [4-

5] min at 190 °C) and low enthalpy recorded in DSC (22.6 kJ/mol versus 49.9 kJ/mol for di-vanillin

Bz for example).

In consequence, the di-cardanol Bz monomer is interesting because of its low melting

temperature but the corresponding PBz material elaboration is nevertheless impeded by a long

gelation time and steric hindrance resulting in a poorly crosslinked polymer material. The use of

the di-vanillin Bz monomer to synthesize a self-standing PBz material on the contrary is hindered

by a too high melting temperature overlapping its polymerization and thermal degradation.

However, the good thermal properties of di-vanillin PBz due to the aldehyde function of vanillin

Bz are very encouraging.

Thus, we propose an innovative strategy to lower vanillin-based Bz monomers melting

temperatures in order to enable their processing. Cardanol was shown to provide, through

plasticizing effect of the C15 alkyl chain, flexibility to the resulting materials and to result in Bz

monomer with low melting temperature. More importantly, the low reactivity of cardanol driven

by its structural features offers therefore the possibility to control the synthesis of a mono-

cardanol Bz with a free primary amine moiety that can be further coupled with another bio-based

phenol like vanillin. We propose in the following part a synthesis of asymmetric monomers

combining cardanol and vanillin displaying low melting temperature and accessing PBz materials

with good thermo-mechanical properties.

2.2 Asymmetric benzoxazine monomers synthesis and characterization

2.2.1 Asymmetric Bz monomer synthesis

Accordingly, with an appropriate adjustment of the reagents stoichiometry, asymmetric

benzoxazine monomers were synthetized (cardanol, EDA, paraformaldehyde reacted in CHCl3 at

70 °C under reflux in stoichiometric ratio 1:1:2), mono-substituted cardanol-benzoxazine was

133

obtained. To produce the so-called Vani-Card asymmetric Bz monomer, vanillin was added in a

second step to the precedent reaction crude with paraformaldehyde in stoichiometric ratio 1:2

and reacted at 70 °C (Figure III - 38).

Figure III - 38. Synthesis of the asymmetric Vani-Card Bz monomer from cardanol and vanillin.

High yield (72 %) of Vani-Card Bz monomer was obtained as confirmed by 1H NMR and HRMS

(Figure III - 39 and - 40 respectively).


The recorded 1H NMR spectrum of Vani-Card is displayed in Figure III - 39. The spectrum

revealed the presence of characteristic peaks corresponding to the formation of the asymmetric

Bz monomer.

As previously mentioned, the precise integration of the NMR signals corresponding to peaks

relative to the cardanol compound, depends on the composition of cardanol and related

proportion of different isomers. The integrations are usually calculated by moderation based on

the abundance of unsaturation described in the literature. In addition to varying unsaturation

abundances, the difference of relaxing times between aromatic and aliphatic hydrogen may

complicate the precise quantification of all hydrogen from this asymmetric monomer.

An accurate integration was optimized where the –OCH3 function from the vanillin compound

was taken as integration reference for the peaks corresponding to the benzoxazine structure. This

peak should integrate for 3 H. As the cardanol alkyl chain unsaturation degree is varying and the

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relaxation times are differing from the other hydrogens, the related peaks will be integrated on

another reference. The aliphatic hydrogen in β position of the cardanol aromatic ring was taken

as integration reference and should integrate for 2 H.

Figure III - 39. 1H NMR spectrum (in CDCl3) of Vani-Card benzoxazine monomer.

First of all, the characteristic peaks of cardanol were observed, such as the aromatic protons [1,

2, 3] at δ = 6.60 – 6.88 ppm which integrate each for about 1 H (see Table III - 16) indicating

probably the presence of only one cardanol moiety within the monomer. This was further

corroborated by the integration of the remaining peaks from cardanol, the alkyl chain olefinic CH2

protons [b2, d2, e2, g2, h2, a2] at δ = 4.96 – 5.88 ppm, the protons in α of the alkyl chain

unsaturations [c2, f2, i2] at δ = 1.98 – 2.09 ppm, as well as the CH2 protons in α of the aromatic [o]

at δ = 2.49 – 2.57 ppm, the CH2 from the alkyl chain [b1, c1, d1, e1, f1, g1, h1, i1, j, k, l, m, n] at δ = 1.23

– 1.43 ppm and the CH3 of the alkyl chain [a1] at δ = 0.86 – 0.94 ppm. The CH2 of the alkyl chain

comprised between two unsaturations [c3, f3] were detected at δ = 2.76-2.87 ppm. The

experimental and theoretical integrations of the peaks corresponding to the cardanol moiety of

the Vani-Card monomer are reported in the Table III - 16 with the aliphatic hydrogen in β

position of the cardanol aromatic ring, as integration reference (I = 2 H). As it can be observed,

the experimental integrations of the peaks corresponding to the cardanol moiety are close to the

expected integrations for Vani-Card Bz monomer containing one cardanol moiety.

For the vanillin moiety of Vani-Card Bz monomer, the peak corresponding to the –OCH3 function

of vanillin [13] at δ = 3.86 – 3.94 ppm was chosen as integration reference. This peak should

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integrate for 3H (I = 3 H). The characteristic peaks corresponding to the vanillin compound

moiety were revealed in the NMR spectrum. The hydrogens from the aldehyde function [11]

appeared at δ = 9.81 ppm with Iexp = 1.01 H (Ith = 1.00 H). The integration of aromatic proton of

vanillin [10, 12] at δ = 7.12 - 7.34 ppm further confirmed the presence of one vanillin moiety (Iexp

= 1.00 and 1.01 H and Ith = 1.00 and 1.00 H). Peaks corresponding to EDA [6, 7] were also observed

at δ = 2.95 – 3.09 ppm where Iexp = 3.99 H (Ith = 4.00 H).

Furthermore, characteristic peaks at δ = 4.01 ppm and δ = 4.13 ppm assigned to Ar-CH2-N of

cardanol- [4] and vanillin-based [9] oxazine moieties respectively were detected, as well as at δ =

4.88 ppm and δ = 5.08 ppm assigned to O-CH2-N of cardanol- [5] and vanillin-based [8] oxazine

moieties respectively, attesting the formation of an asymmetric di-Bz monomer from vanillin and

cardanol.

Chemical shift

(ppm) Assignment

Compound

reference Iexperimental Itheoretical

0.85 – 0.96 -CH3

[a1] cardanol 2.04 H 1.77 H

1.23 – 1.41

-CH2

[b1, c1, d1, e1, f1,

g1, h1, i1, j, k, l, m,

n]

cardanol 13.53 H 13.56 H

1.54 – 1.64 -CH2 in β from Ar

[n] cardanol Ref 2.00 H 2.00 H

1.98 – 2.09 CH2*=CH

[c2, f2, i2] cardanol 3.41 H 3.10 H

2.49 – 2.56 CH2-Ar

[o] cardanol 2.00 H 2.00 H

2.75 – 2.87 CH2*(=CH)2

[c3, f3] cardanol 2.36 H 2.10 H

2.95 – 3.09 N-CH2*-CH2

[6, 7] benzoxazine 3.99 H 4.00 H

3.86 – 3.94 O-CH3

[13] Benzoxazine Ref 3.00 H Ref 3.00 H

4.01 Ar-CH2-N

[4] cardanol 1.99 H 2.00 H

4.13 Ar-CH2-N benzoxazine 1.99 H 2.00 H

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[9]

4.88 O-CH2-N

[5] cardanol 1.98 H 2.00 H

4.96 – 5.88

CH=

[b2, d2, e2, g2, h2,

a2]

cardanol 1.00; 3.76; 0.46 H 0.82; 3.24; 0.41

H

5.08 O-CH2-N

[8] benzoxazine 1.99 H 2.00 H

6.60 – 6.99 H-Ar

[1, 2, 3] cardanol 1.07; 1.06; 1.00 H

1.00; 1.00; 1.00

H

7.12 – 7.34 H-Ar

[10, 12] benzoxazine 1.00; 1.01 H 1.00; 1.00 H

9.81 (C=O)H

[11] benzoxazine 1.01 H 1.00 H

Table III - 16. Assignments of the 1H NMR peaks of the asymmetric Vani-Card Bz monomer and


2.2.3 Characterization by MALDI-TOF/MS

The asymmetric Bz monomer was also successfully detected by mass analysis (Figure III – 40a)

as the protonated Vani-Card specie was observed at m/z 559, as well as the expected ions

[M+H+H2O-CH2O]+ at m/z 547 and [M-H+H2O-CH2O]+ at m/z = 545.

The theoretical expected mass of Vani-Card is displayed on Figure III – 40b. The mass found for

the asymmetric monomer m/z 559.3531 is very close to the theoretical mass expected of m/z

559.3530, confirming the formation of the expected Vani-Card monomer.

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Figure III - 40. HRMS analysis of Vani-Card Bz monomer a) Zoom of the experimental product


Nevertheless, some additional peaks could be observed around m/z 400 (Figure III – 41). Those

peaks at m/z 399, 383 and 358 on the Vani-Card spectrum were resulting from the monomer

fragmentation during the mass analysis timeframe of the cardanol-based benzoxazine part of the

Vani-Card monomer. Indeed, as it can be observed on the MS/MS spectrum of the di-cardanol

monomer (Figure III - 32), some peaks resulting from fragmentation were readily detected at

m/z = 399-405, 383-387 and 358.

Figure III - 41. HRMS spectrum of Vani-Card benzoxazine monomer.

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2.2.4 Characterization by DSC

The thermal behaviour of the asymmetric Vani-Card Bz monomer was investigated by DSC

analysis, and compared to the symmetric di-vanillin and di-cardanol Bz monomers. For each

monomer, the DSC analysis was carried out at a heating rate of 20 K/min under nitrogen

atmosphere.

The DSC analyses of the asymmetric Vani-Card Bz monomer and of the symmetric di-vanillin and

di-cardanol Bz monomers are displayed in Figure III - 42.

Figure III - 42. DSC thermograms (N2, 20 K/min) of a) di-vanillin, b) Vani-Card Bz monomers

and c) di-cardanol Bz monomer.

Alike symmetric Bz monomers, the DSC thermograms of the asymmetric monomer (Figure III -

42b) showed an endothermic peak corresponding to the monomer melting temperature around

101 °C, and an exothermic peak, in the range of 200-250 °C, assigned to the curing by thermal-

activated ring-opening of the Bz monomer. It can be noticed that the melting temperature was

significantly decreased from Tm = 218 °C recorded for di-vanillin Bz to Tm = 101 °C for Vani-Card

enlarging therefore the processing temperature frame. The drastic melting temperature decrease

when substituting one vanillin moiety by cardanol compound is attributed most likely to the C15

alkyl side chain that disturbed the ordered structure of di-vanillin benzoxazines. Interestingly,

139

the temperatures of the ring-opening polymerization were slightly affected and remained in the

range of catalyst-free ring-opening reactions of Bz regardless the nature of the phenol. Indeed, Tp

shifted only from 225 °C to 227 °C for di-vanillin and Vani-Card Bz monomers respectively. These

results were consistent with those reported by Allen et al.209 who evidenced that the phenol

substitution strongly impacts the melting temperatures of Bz monomers, without influencing the

ring-opening polymerization temperature.

Moreover, it is important to notice that contrary to the di-vanillin Bz monomer, the thermal

degradation of Vani-Card Bz monomer occurred at higher temperature (T5% = 280 °C) than its

polymerization temperature (Tp = 227 °C) (Figure III - 43), further confirming the possibility of

elaborating PBz material from the Vani-Card Bz monomer.

Figure III - 43. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of the Vani-Card Bz

monomer.

2.2.5 Characterization by rheology analysis

Rheology experiment was monitored for the asymmetric Bz monomer in order to evaluate its

polymerization reactivity and to compare it to the reactivity of the symmetric di-cardanol Bz

monomer. The polymerization measurements were achieved with plate-plate geometry

(diameter 25 mm, measure gap 0.5 mm) and recorded at an imposed 1 % deformation at 1 Hz

frequency at 190 °C. Full plot rheogram is depicted in Annex Figure 3 p 191.

From a processing point of view, first and foremost, the synthesized asymmetric Vani-Card Bz

exhibited a moderate gelation time ([8-9] min at 190 °C, Figure III - 44) as opposed to di-cardanol

monomers for which the gelation time was very long at the same temperature, and to the di-

vanillin monomer which polymerization could not be recorded by rheology due to its high melting

temperature and close degradation temperature. Vani-Card gelation time was far below values

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reported for relevant bis-phenol-A/aniline Bz cured at 190 °C for which is around 39.9 min for

example.210

Figure III - 44. Isothermal rheology monitoring of Vani-Card (circular markers) and di-cardanol

(triangular markers) benzoxazines at 190°C – empty markers: storage modulus G’; filled

markers: loss modulus G’’.

The Vani-Card Bz monomer displays thus an enhanced reactivity, highlighted by a relative low

gelation time in comparison to a di-cardanol Bz monomer.

The properties of the symmetric and asymmetric Bz monomers are summarized in Table III - 17.

Bz monomer Tm a (°C) Tp a (°C) ∆H a (kJ/mol) T5% b (°C) Tgel c (min)

di-Vanillin 218 225 49.9 203 -

di-Cardanol 44 219 22.6 260 [30-31]

Vani-Card 101 227 45.0 280 [8-9]

Di-phenol 115 212 - 287 [4-5]

Table III - 17. Thermal properties of symmetric and asymmetric di-benzoxazine monomers.

Values are obtained from DSC (a), TGA (b) and rheology (c) analyses.

In Table III - 17 are also reported the melting and polymerization temperatures of a model

benzoxazine monomers prepared from the bridging of two phenols with ethylenediamine (so-

called di-phenol). Di-phenol Tm (115 °C) and Tp (212 °C) (Figure III - 33,) are similar to those of

Vani-Card, emphasizing the capability of Vani-Card to be processed as well as a short amine

bridged petroleum-based benzoxazine monomer.

141

In conclusion, the Vani-Card Bz monomer, through interesting properties of such as a low Tm and

thus a moderate processing window, as well as a high thermal degradation temperature and a

relative short gelation time, appears as a promising precursor for the elaboration of bio-based

PBz material with good properties.

2.3 Materials elaboration and characterizations

2.3.1 Materials elaboration

Polybenzoxazine materials were elaborated from the symmetric di-cardanol Bz monomer as well

as from the asymmetric Vani-Card Bz monomer, and their characteristics were compared.

The monomers were degassed during 1 h above melting temperature (50 and 105 °C, for Vani-

Card and di-cardanol Bz respectively) and then transferred to a U-shaped mold. A curing program

of 1 h at 160 °C was applied followed by 2 h at 180 °C and the samples were post-cured for 2 h at

200 °C and 30 min at 220 °C.

2.3.2 DMA characterization

DMA characterizations of polymerized Vani-Card and di-cardanol Bz, so-called poly(Vani-Card)

and poly(di-cardanol), are reported on Figure III - 45. Surprisingly, poly(di-cardanol) started

creeping above 80 °C as attested by the absence of caoutchoutic state in its thermo-mechanical

behaviour and confirmed by the picture of the material at the end of the test, inserted in Figure

III - 45. On the contrary, the asymmetric poly(Vani-Card) presented a thermoset-like behaviour

upon heating and its Tα was reached at 129 °C, according to the maximum of the tan δ peak.

The cardanol side chain had a clear plasticization effect on both materials (symmetrical and

asymmetrical based on cardanol) as compared to the Tα of poly(di-phenol) (160 °C), but resulted

in a thermoplastic material in the case of poly(di-cardanol). The substitution of one unit of

cardanol by vanillin within the monomer allowed a sufficient increase of the Vani-Card PBz

crosslinking density to yield a self-supported thermoset material.

In addition, the vanillin formyl group within the material should increase the material stiffness

most probably through the formation of strong intra- and inter-molecular H-bonding. The storage

modulus in the glassy state also increased from 150 MPa for poly(di-cardanol) to 700 MPa for

poly(Vani-Card). These values of storage modulus seemed to be similar to those described in the

literature. Ishida and Agag reported a storage modulus of 450 MPa in the glassy state for a

polybenzoxazine prepared from CNSL and aromatic 4,4’-diaminophenyl methane.211 In spite of

the aromatic diamine used by the authors, poly(Vani-Card) enabled to reach a material with

higher stiffness due to the presence of the vanillin moiety.

142

Figure III - 45. DMA thermograms of poly(di-cardanol), poly(di-phenol) and poly(Vani-Card).

The DMA analysis of the asymmetric poly(Vani-Card) material revealed the elaboration of a self-

supported PBz material from the Vani-Card Bz monomer displaying good thermal properties in

comparison to a traditional poly(di-phenol) material.

Finally, the new poly(Vani-Card) material was compared in term of thermal stability by

thermogravimetric analyses under air atmosphere to poly(di-cardanol) and poly(di-phenol)

(Figure III – 46).

As poly(di-vanillin) could not be elaborated, we report on Figure III - 46 the evolution of the

percentage of mass loss (wt%) for a poly(di-phenol) for the sake of comparison. The onset

degradation temperature of poly(di-phenol) was quite low (around 230 °C) due to the

fragmentation of the Schiff bases. The presence of cardanol in poly(Vani-Card) and poly(di-

cardanol) seemed to prevent this first degradation step. Yet, the onset of the thermal degradation

for poly(Vani-Card) and poly(di-cardanol) materials were unexpectedly high (T5% = 373 °C and

398 °C respectively) given the presence of unsaturation that are commonly known to promote

the chain scission and therefore the thermal degradation of polymers.

In conclusion, the TGA analysis of the symmetric and asymmetric PBz materials highlighted the

increase of the thermal degradation temperature for PBz materials containing at least one

cardanol moiety (poly(di-cardanol) and poly(Vani-Card)).

143

Figure III - 46. TGA (air atmosphere, 20K/min) thermograms of a) di-cardanol, b) di-phenol

and c) Vani-Card PBz materials.

The thermal and mechanical properties of the symmetric poly(di-cardanol) and poly(di-phenol)

and of the asymmetric poly(Vani-Card) materials are gathered in Table III - 18.

PBz materials Tg (°C)a T5% b (°C) Tmax b (°C)

Poly(di-Cardanol) - 398 456

Poly(Vani-Card) 129 373 440

Poly(Di-phenol) 160 273 407

Table III - 18. Thermal properties of symmetric and asymmetric PBz materials. Values are

obtained from DMA (a), and TGA (b) analyses.

3 Conclusions

In conclusion, the first part of this study highlighted the difficulty to synthetize PBz materials from

bio-based di-Bz monomers. Indeed, elaboration of a PBz material from di-vanillin Bz monomer

for example was strongly hampered by the high melting temperature of the monomer Tm = 218

°C), overlapping the polymerization (Tp = 225 °C). On the contrary, di-cardanol Bz monomers

presented the great advantage of displaying a low melting temperature (Tm = 44 °C), facilitating

the materials processing (ΔTproc = 175 °C). Due to the sterical hindrance of the cardanol alkyl side

chain, the material was poorly crosslinked and started creeping around 80 °C. Finally, this

roundabout was allowing the synthesis of an easy processable thermoplastic material based on

PBz, which is quite rare in the literature.

With the aim to combine the good thermal properties of vanillin-based Bzs (possible H bonding

through the aldehyde function) and the low melting temperature of the cardanol-based Bz

144

monomer, we reported an efficient preparation of asymmetric bio-based di-benzoxazines (named

Vani-Card) via a two-step synthesis pathway including a controlled mono-substitution of

cardanol-based benzoxazines followed by a coupling with vanillin. Such combination resulted in

a substantial decrease of the melting temperature (Tm = 101 °C), without any impact on the

activation temperature (Tp = 227 °C) enlarging therefore the processing window of these bio-

based thermosets (ΔTproc = 126 °C, compared to ΔTproc = 7 °C for di-vanillin Bz). Furthermore, a

second drawback of the di-vanillin Bz monomers was their thermal degradation occurring

simultaneously to their melting and even before their polymerization (T5% = 203 °C). In the case

of the asymmetric Vani-Card Bz monomer, no problem of thermal degradation of the monomer is

further encounter due to the presence of the cardanol moiety. Indeed, the thermal degradation of

the Vani-Card monomer occurred at higher temperature than melting and polymerization (T5% =

280 °C).

The asymmetric Bz monomer enabled thus, through a processing point of view, an easy

elaboration of a cardanol- and vanillin-based PBz material. Furthermore, the synthesis of the

asymmetric Vani-Card monomer was also shown to strongly influence the reactivity of the

monomer. Indeed, the di-cardanol Bz monomer displayed a long gelation time (Tgel = [30-31] min

at 190°C) in comparison to a classical di-phenol Bz monomer (Tgel = [4-5] min at 190°C). In the

case of Vani-Card Bz, an interesting moderate gelation time of 8-9 min was reported.

Moreover, the characterizations of the asymmetric PBz material highlighted the obtaining of a

thermoset material with good thermo-mechanical properties. Indeed, a Tg of 129 °C and a storage

modulus in the glassy state of 700 MPa were reported, indicating that Vani-Card PBz material

displayed very comparable thermal and mechanical properties to other known polybenzoxazines

particularly those partially or fully based on renewable compounds.

Finally the presence of the cardanol moiety was shown to strongly influence the thermal stability

of the PBz material. Indeed, a high thermal degradation onset temperature was recorded for Vani-

Card PBz material (T5% = 373 °C) compared to classical di-phenol PBz material (T5% = 273 °C).

This versatile approach is a powerful tool to access a wide range of bio-based asymmetric

benzoxazines given the large number of precursors available and their possible combination. It

paves the way toward easily processable high performance bio-based benzoxazines. This strategy

could for example be applied to further improve the processing of bio-based di-Bz monomers.

Indeed, the high polymerization temperature of Bz monomers remains a major drawback for

their spreading for industrial applications. The use of lignin-derivative phenolic compounds

bearing a carboxylic acid function for the synthesis of mono-Bz monomers were recently reported

by Comi et al.184. The presence of the –COOH function was reported to induce a lowering of the Bz

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ring opening polymerization temperature. However, among others, the main drawback of these

monomers was there to high melting temperature, close to their polymerization temperature,

hindering the processing of the materials. The synthesis of asymmetric monomers between

cardanol and bio-based phenolics bearing carboxylic acid functionalities could be an interesting

method to lower the polymerization temperature of the Bz while facilitating their processing.

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Chapter IV: Interpenetrating Polymer Networks (IPN) from a cardanol-based thermoset network

1 Introduction

Nowadays, the use of conventional petroleum-based epoxy thermosets is being compromised not

only for the foreseen shortage in oil resources, but also because widely used components such as

Bisphenol A (BPA), identified as an endocrine disruptor, wreak havoc on the human health. This

is why researchers are focusing on the development of totally or partially bio-based and potential

environmentally friendly BPA-free epoxy thermosets. Among the most promising bio-based

alternatives, cardanol has attracted a tremendous level of interest within the materials

community. In particular, di-glycidyl ether of cardanol (CDGE) (Figure IV - 1) could be considered

as a viable alternative to traditional thermosets prepared from BADGE.

Figure IV - 1. Chemical structure of diglycidyl ether of cardanol (CDGE) – commercially

available NC514 - from Cardolite Corporation.

However, its low thermal and water resistance properties are important drawbacks to a wider

range of applications. Reinforcement of CDGE-based networks could be performed from a

macromolecular approach by the interpenetration of a polybenzoxazine network. Indeed, as

described earlier in this manuscript, benzoxazines have excellent thermal properties and have

the clear asset to not swell anymore in any kind of solvent once they are polymerized. However,

their interpenetration within epoxy networks remains a challenge due to competitive chemical

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reactions. In particular, amines used for the crosslinking of epoxy networks are also able to

catalyse the ring opening polymerization of benzoxazine monomers, or even to react with them,

preventing thus the formation of clear IPNs. The following chapter deals with this topic, and

reports the preparation of IPN of CDGE network with a model polybenzoxazine network. A state-

of-the art of CDGE is first reported to introduce this topic.

1.1 Cashew nutshell diglycidyl ether

CDGE is a commercially available product, produced by Cardolite and supplied under the

trademark NC514 (Figure IV – 2). Researchers firstly focused on its molecular characterization

because of its wide molecular diversity. Indeed, as previously mentioned, cardanol is composed

of four molecules with a variable unsaturations rate. CDGE epoxy resin is obtained by the

phenolation of cardanol unsaturations through Friedel-Craft reaction and followed by the

epoxidation of the hydroxyl groups by reaction with epichlorohydrin.35

Figure IV - 2. Friedel-Crafts alkylation of phenol with cardanol (ideal reaction pathway).

Cardolite indicates an Epoxy Equivalent Weight (EEW) of 490 g/eq for the CDGE epoxy pre-

polymer and the chemical structure represented in Figure IV - 1.

The chemical structure of CDGE pre-polymer was fully characterized by NMR analysis,13 as well

as by size exclusion chromatography (SEC) and MALDI mass spectrometry.204, 212 The resulting

materials properties were also studied.

The NMR analysis of the CDGE pre-polymer allowed the determination of its unsaturation

composition. CDGE contains predominantly saturated chains (95 %) and mono-olefinic chains (5

%) as illustrated in Figure IV - 3.13

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Figure IV - 3. Chemical structure of diglycidyl ether of cardanol determined by 1H NMR

analysis.213

Furthermore, opened epoxy groups were also revealed, a ratio of 70 % of epoxy groups and 30 %

of opened epoxy rings were found to compose the CDGE compound (Figure IV - 4). The

experimental molar mass found by SEC for CDGE (1029 g/mol, polystyrene standard) is higher

than the theoretical molar mass of 460 g/mol indicated by Cardolite. The CDGE compound is thus

a mixture of epoxidized forms of cardanol. These results were moreover confirmed by the

demonstration of possible poly-substitutions of the phenolic ring during phenolalkylation.35 The

chemical structure of CDGE, based on the NMR and SEC analysis, is proposed in Figure IV - 4.

Figure IV - 4. Chemical structure of CDGE obtained from NMR analysis.213

Furthermore, four different structures, determined by MALDI mass spectrometry and depicted

in Figure IV – 5, were found to further compose the CDGE epoxy pre-polymer.204 CDGE was found

to be composed of epoxidized cardanol bearing an additional phenol moiety (Figure IV - 5a),

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epoxidized cardanol containing both an epoxidated and a native phenol on its side chain (Figure

IV – 5b), epoxidized cardanol linked to a native cardanol (Figure IV – 5c), and two epoxidized

cardanol linked by a native phenol (Figure IV - 5d).

Figure IV - 5. Additional chemical compounds composing CDGE determined by MALDI-MS

analysis a) epoxidized cardanol bearing an additional phenol moiety, b) epoxidized cardanol

containing both an epoxidated and a native phenol on its side chain, c) epoxidized cardanol

linked to a native cardanol, d) two epoxidized cardanol linked by a native phenol.204

The chemical structure of CDGE is thus very complex and composed of a significant number of

molecules. However, the lack of purification of this commercial product is not a drawback to its

use, and it is worthy to remind that even very commonly used BADGE pre-polymer (DER332) is

composed of oligomers and it is the reason why its reactivity is averaged and given in EEW.

1.2 CDGE-based thermosets

Jaillet et al. were first to study the elaboration of CDGE networks.213 They investigated the

optimum ratio between the epoxy compound and various amine hardeners, to determine the

corresponding materials with the higher glass transition temperature.

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CDGE epoxy materials were elaborated with isophorone diamine (IPD) and Jeffamine D400 as

crosslinking agents (Figure IV - 6). The corresponding materials were compared to BADGE/IPD

reference epoxy resin. Both crosslinking agents are aliphatic amines with a similar functionality,

but the inherent chemical structure of Jeffamine - composed of a moderate oxypropylene chain

(6.1 units) - leads to very flexible networks. Formulations with a ratio of 1/1 eq for BADGE/IPD

led to the material with the highest Tg of 158°C.

Figure IV - 6. CDGE cross-linking agents a) isophorone diamine and b) Jeffamine D400.

The most suitable ratio between CDGE and IPD was 1 g of CDGE and 0.13 g of IPD, leading to a

material with a Tg = 50 °C. The cardanol alkyl chains act as a plasticizer and soften the network.

When Jeffamine D400 was used in lieu of IPD, the best epoxy/amine ratio was 1 g of CDGE and

0.29 g of Jeffamine, yielding to a material with a very low Tg = 15°C. The CDGE network Tg is thus

highly affected by the Jeffamine diamine flexibility. These results were supported by the

determination of the networks crosslinking densities (ʋe) from the storage modulus at 60 °C

above the Tg, determined by DMA (Table IV - 1). The crosslinking density was calculated by the

following formula developed by Webster et al. 214:

E’ = 3ʋeRT

The lower crosslinking density of the CDGE/IPD network in comparison to the BADGE/IPD

network is explained by the higher flexibility and lower EEW of CDGE.

Epoxy/amine

(amine equivalent) Tg (°C)

E’ (MPa)

at Tg + 60 °C ʋe (103 mol/m3)

BADGE/IPD

158 19.6 4.8

CDGE/IPD

50 3.2 1

CDGE/Jeff400

15 2.6 1

Table IV - 1. Thermomechanical properties of CDGE cured with IPD or Jeff400, compared to

BADGE/IPD network.213

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Similar studies were undertaken by Chrysanthos et al.,212 who reported the elaboration of

CDGE/IPD networks and compared them to BADGE/IPD networks. Analogous results as in Jaillet

et al. were found for a formulation ratio of 1/1 (CDGE/IPD equivalent).

CDGE epoxy pre-polymer was also studied to substitute BADGE for the elaboration of epoxy

thermosets for adhesive applications.215 The adhesive and thermo-mechanical properties, as well

as the water resistance were studied for different compositions of BADGE/CDGE co-networks,

cross-linked with 1,2-diaminocyclohexane (DAC) (Figure IV - 7) in stoichiometric amount.

Figure IV - 7. Chemical structure of 1,2-diaminocyclohexane (DAC) cross-linking agent.

The main weakness of BADGE networks is their low water resistance, and a way to evaluate it is

to perform wet cataplasm tests. The adhesive properties and the water resistance of the

CDGE/DAC network were tested by these pull-off-tests on alumina after wet cataplasm swellings.

During these tests, the assemblies were exposed to water at 80 °C during 4 h and the adhesion

strength was measured after this exposition. Interestingly, neat CDGE/DAC epoxy network

displayed after this test a high adhesive strength (4.5 MPa), even higher than dry neat

BADGE/DAC network adhesion strength (4 MPa). Thus the more sensitive to water is the

network, the lower is the adhesion strength after wet cataplasm test. Indeed, higher strengths

were due to better surface wettability (Contact angles values obtained by elliptic calculation

method: 66 ± 2 °for BADGE and 51 ± 1 ° for CDGE) leading to stronger aluminium-epoxy joints.

These results are highlighting the interesting properties of CDGE-based materials to substitute

Bisphenol A diglycidyl ether in adhesive applications in wet environments. However, in spite of

this relatively high resistance to water, certainly linked to the very limited hydrolysis of CDGE

network compared to BADGE, CDGE swells too much in water. Even if the impact on the Tg is very

low, one can imagine that 5 % volume change would be problematic for a lot of applications. The

addition of fillers, like clay of expanded graphite, is a well-known approach that would limit the

diffusion of H2O molecules within the network. In this work, we decided to consider another

approach based on a macromolecular reinforcement. The following parts are focusing on the

state-of-art of the macromolecular reinforcement of epoxy networks, and more particularly on

the use of benzoxazine.

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1.3 Reinforcement strategies: macromolecular reinforcement of epoxy networks

Owing the high performance properties of polybenzoxazines, their use as reinforcement for the

cardanol-based epoxy material – CDGE - has been foreseen in the following chapter. Indeed,

polybenzoxazines materials are known to have excellent thermo-mechanical properties and high

stiffness. Their use as reinforcement of the epoxy network properties appears thus as a promising

opportunity. Nevertheless, despite the advantageous properties of polybenzoxazine materials,

their high brittleness and low cross-linking density, in comparison to epoxy thermosets for

example, are the major drawbacks of polybenzoxazine materials. The particular properties of

PBz are explained by the formation of strong H-bonding between the phenolic hydroxyl groups

and the tertiary amines of the Mannich linkages formed by ROP.129-132 Thus, to date, the majority

of the works reported on polybenzoxazine and epoxy resins aimed at the the improvement of the

flexibility of benzoxazine resins by co-reactions and co-crosslinking with epoxy resins.216

1.3.1 State of the art of the epoxy/benzoxazine based co-networks

In several recent works, co-networks between epoxy and benzoxazine resins have been reported

to successfully improve the thermal and mechanical properties of the resulting material. As

benzoxazine monomers are reactive towards amines, but also towards the epoxy groups

themselves, various strategies have been considered for the reinforcement of benzoxazines by

co-polymerization with epoxy resins.

1.3.1.1 Epoxy/benzoxazine

Ishida et al. 217 were first to report the preparation of PBz/epoxy co-networks by the reaction

between the epoxy groups and the phenolic hydroxyl group issued from the opening of the

oxazine ring (Figure IV - 8). In this work, BADGE was reacted with a bisphenol-A based

benzoxazine in weight proportion 30/70. An increase of the Tg (from 141 °C to 156 °C) was

observed due to the additional cross-linking density added by the benzoxazine molecules.

Figure IV - 8. Synthesis of Pbz/epoxy co-networks.217

This approach is nevertheless limited to systems containing a major part of benzoxazine. Indeed,

a too high amount of epoxy groups would lead to a decrease of the crosslinking density due to

unreacted or small molecular weight epoxy acting as plasticizer within the PBz resin. Similar

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results were obtained by Jain et al..218 The activation of the Bz ROP by the BADGE compound is

attested by the decreasing of the benzoxazine polymerization temperatures. Nevertheless, the Tg

was also found to decrease with an increase of the BADGE amount.

Interestingly enough, these systems were shown to be very stable at high temperature since the

polymerization was triggered by the oxazine ring opening that occurs around 150 °C for

bisphenol-A based benzoxazine. Based on this property, Kimura et al.219 developed a new epoxy

precursor from the combination of BADGE and PBz stable at elevated temperatures for injection

molding. The PBz cured BADGE thermoset displayed even a higher Tg (175 °C) than the BADGE

thermoset cured with novolac (phenol-formaldehyde resin, Tg = 149 °C).

Epoxy materials are generally cured with multifunctionnal amines, and it is conceivable to use

them in combination to benzoxazine.216, 220-227 Several reactions described hereafter are likely to

occur in these ternary systems, influencing the final material morphology and properties.

Benzoxazine monomers were shown to react with epoxy groups after their ring opening (Figure

IV – 8). In particular, benzoxazine monomers are reactive towards primary amines (Figure IV -

10) used to crosslink epoxy networks. Such a reaction occurring at low temperature, would lead

to a competition with the epoxy/amine cross-linking reaction (Figure IV – 9).

Figure IV - 9. Reaction between epoxy and primary and secondary amine functions.

1.3.1.2 Epoxy/amine/benzoxazine

Grishchuk et al. 216 investigated the effect of common diamines usually used as epoxy hardener,

such as diethylenetriamine (DETA) and 4,4’-diaminodiphenyl methane (DDM) on the

polymerization of a Bisphenol A/aniline Bz (BA-a). DSC analysis of BA-a revealed a single

exothermic signal with a maximum at Tp = 253 °C corresponding to the opening of the oxazine

ring. The addition of a diamine compound, whatever it is, led to the same trend as illustrated by

the shift of the exotherms to lower temperatures: the diamine triggers the opening of the oxazine

rings at lower temperatures.

Concerning this topic, a throughout study has been published by Endo et al. 228 describing the

effect of the chemical structure of a large set of diamines onto Bz polymerization. The hardeners

donate a proton to the benzoxazine monomer, resulting in an anion able to eventually attack the

electrophilic iminium intermediate. Clearly, the benzoxazine compound acts as a nucleophile

towards the proton in this case and the lone pair of the nitrogen of the oxazine ring is thought to

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be the most reactive position. Therefore, it is expected that a series of reactants can open the

oxazine ring via a nucleophilic attack to the electrophilic portion at the C8 carbon atom (Figure

IV - 10).

Figure IV - 10. Reaction scheme of opening the oxazine ring via an amine nucleophilic attack.229

The addition of an amine achieved a much faster polymerization at mild temperatures, and the

efficiency of the diamine onto the ROP of benzoxazine is directly depending on its basicity. The

authors of this work evidenced the following order: arylamine > alicyclic amine > alkylamine.

In summary, it is easy to expect that mixtures of epoxy /diamines /benzoxazines will all react

together if the curing is not controlled. Indeed, Wang et al. 227 evidenced that the morphology of

the networks may be affected by the curing process. The curing of a ternary system composed of

Bisphenol A-based benzoxazine, BADGE, and imidazole at 180°C led to the simultaneous reactions

of all the compounds together (epoxy/imidazole, Bz/imidazole, Bz/epoxy, and Bz

homopolymerization). By starting the reaction at a lower temperature (80 °C), the diamines

reacted first with the epoxy group leading first to the formation of the epoxy network, and

consuming all the epoxy and imidazole compounds. This first step was then followed by the

formation of the PBz network during the post-cure at 180 °C through the homo-polymerization

of the Bz monomers.

In consequence Wang et al. highlighted that the control of the curing conditions of

epoxy/diamine/Bz system could lead to the formation of a material mainly composed of two

distinguished structures: an epoxy-amine network and a polybenzoxazine network. These results

pave the way to the possible elaboration of IPN based materials between epoxy and Bz which will

be subsequently studied.

1.4 Epoxy/polybenzoxazine IPNs

Sperling defines IPNs as the combination of two, or more, polymer networks that are synthesized

in juxtaposition. According to the IUPAC, “an IPN is a polymer comprising two or more polymer

networks which are at least partially interlaced on a molecular scale, but not covalently bonded to

each other and cannot be separated unless chemical bonds are broken”.230

IPNs can be synthetized from two synthetic pathways: sequential synthesis or in-situ synthesis.

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In the sequential synthesis method, a first network is formed and subsequently swollen with the

reagents of the second network, which is then synthesized inside the first network (Figure IV -

11). By this method, the morphology is generally imposed by the first network, and the IPN

composition range is limited by the maximum swelling of the first network by the second network

reagents.

Figure IV - 11. Sequential synthesis of IPN.

In the in-situ method, all reagents are mixed at the beginning of the synthesis. The two network

formations can be, or not, started simultaneously (Figure IV - 12). It is necessary for the two

network formation mechanisms to be different and independent. Otherwise, a single polymer, or

copolymer network or a co-network is obtained. By this method, the ratio of the two networks

can be almost freely modified by adjusting the reagents proportions.

Figure IV - 12. In-situ IPN synthesis.

The two synthetic methods allow the association of cross-linked polymer networks of different

chemical nature. The properties and the morphology of the obtained materials can be adjusted

by modifying the partner proportions, the formation rates of each network compared with the

other, the thermo-dynamical phenomena driven the phase separation (before crosslinking) of

most polymers. Thus IPNs undergo phased separation, but at a smaller scale, than non-

crosslinked polymer blends. During polymerization and network formation, the polymer molar

weights increases, the mixture deviates from equilibrium, and demixing appears. The network

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formation opposes to the phase separation and thus the faster the network formation and the

smaller the obtained domains.

Phase separation in the polymer blends can occur according to two mechanisms, depending on

the temperature and composition of the mixture. First, in a nucleation/growth mechanism,

nodules of one of the two components are forms. These nodules increase with time and eventually

percolate during phase separation (Figure IV - 13).

Figure IV - 13. Nucleation and growth mechanism.

The spinodal decomposition mechanism is also possible. This mechanism produces materials in

which domains with a high concentration of one polymer are dispersed in a matrix with a high

concentration of the second polymer. It corresponds to a meta-stable system in which domains

with complex shapes appear. Chemical composition of these domains evolves with time; each

species becomes predominant in one of the domains with time. This mechanism creates a co-

continuity of the two phases that is also named as gyroïdal structure (Figure IV - 14).230

Figure IV - 14. Gyroïdal structure.

The phase separation mechanism depends on the proportion of the two polymers.

Nucleation/growth mechanism is favoured if one of the precursors is in low concentration. As the

concentration of this component increases a mixture of discrete nodules and complex domains

formed by spinodal decomposition are observed. If the two components are present in equal

amounts, phase separation often occurs by a spinodal decomposition mechanism and two co-

continuous phases are obtained.231

Thermosets can be reinforced at the macromolecular scale by blending with a second polymer or

by the formation of IPN. The IPN structure is considered as an interesting method for the

reinforcement of epoxy materials as the properties of the two polymers are combined in a novel

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material displaying ideally a single glass transition temperature, witnessing the close vicinity of

the two kinds of polymer chain. The single transition temperature, situated between the

transition temperatures of the single networks, corresponds to the interpenetrating phase.

Nevertheless, IPNs show usually two transition temperatures, corresponding to the two phases

induced by the polymer phase separation and enriched in one polymer network.

Epoxy materials are compatible with a wide range of thermoset polymers and are often co-

reactive. Epoxies have thus been blended with almost all the other families of polymers. Similarly,

numerous studies report the toughening of epoxy resins by the formation of IPNs with

polyurethane resins.232-235 Isocyanate-terminated polybutadienes,236 and polyesters,237 were also

considered for the improvement of epoxy properties.

IPNs were mainly used for the improvement of the elasticity, the brittleness or the adhesive

strength of epoxy networks, while maintaining their good thermal properties. To this aim, the

most commonly used polymers are polyurethanes 238 239 or bismaleimides.240 Their incorporation

within the epoxy thermosets allows the improvement of the materials flexibility and its thermo-

mechanical properties. Owing to their excellent thermo-mechanical properties and high stiffness,

polybenzoxazines could be used similarly to polyurethanes and bismaleimides to reinforce CDGE.

The poly(CDGE) single network crosslinked by DAC was shown to display low Tg at 40 °C and a 4

GPa storage modulus in the glassy state.215 Furthermore, Verge et al. reported the high water

uptake of 6 ± 0.2 wt% of a poly(CDGE) network with DAC as hardener, most probably due to its

wide network meshes. On the contrary, the single poly(EDBz) network was shown to display

relatively high Tg of 216 °C and high modulus (6-7 GPa). Furthermore, PBz materials are well-

known for their very low water uptake.115 In consequence, the elaboration of

poly(CDGE)/poly(EDBz) IPN was foreseen as a strategy to reinforce the properties of the

poly(CDGE) network, while preventing the water diffusion by the presence of the poly(EDBz)

network.

This chapter relates the elaboration of interpenetrating polybenzoxazine and epoxy/diamines

networks. By this strategy, we expect to tackle the main issue from CDGE networks, i.e. the water

uptake. Indeed, we envision that the “filling” of the wide mesh of the cardanol-based network by

a PBZ prevent the water diffusion, in addition of clear reinforcement of the thermal and

mechanical properties of the materials. As above mentioned, many competitions may occur

within ternary benzoxazine/epoxy/amines systems and suitable conditions for the elaboration

of IPN have to be found. They are detailed in the following paragraphs.

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The detailed experimental conditions are reported in annex p 181.

2.1 Choice of the system

2.1.1 Sequential in-situ preparation of IPN

First of all, the choice of the IPN elaboration method is in part determining the choice of the

various reagents. In the present study, the choice of the reagents and the curing conditions will

be investigated with the aim to tend toward the in-situ sequential IPN synthesis method. Indeed,

by this synthesis way, the ratio of the two networks can be almost freely modified by adjusting

the reagents proportions, allowing the study of the materials properties depending on their

composition.

With the aim to elaborate IPN materials by in-situ sequential synthesis, the expected reactions

are depicted in Figure IV – 15a.

Figure IV - 15. a) Expected reactions during the IPN sequential in-situ synthesis, b) in-situ

sequential synthesis of a poly(CDGE)/poly(Bz) IPN material.

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As it can be observed, two distinct reactions will be favoured for the in-situ sequential IPN

elaboration. In a first time the polymerization of the epoxy-amine network (poly(CDGE)) between

CDGE and the suitable diamine hardener is expected, followed in a second time, by the ring-

opening polymerization of the Bz monomer forming the polybenzoxazines network. It is

important to notice that any possible reaction between the Bz monomer and the diamine

hardener is to avoid, leading otherwise to co-networks. The choice of a diamine hardener non-

reactive towards the Bz monomer is thus to favour. Furthermore, it is well-known that Bz

monomers polymerize at high temperatures, in the range of 200 °C to 220 °C. In consequence, the

elaboration of the IPNs through the in-situ sequential synthesis is only possible if the epoxy-amine

system cures at low temperature, whereas the PBz network cures at elevated temperature.

Moreover, the possible reaction between amines and Bz monomers have to be similarly avoided.

In conclusion, the choice of the diamine hardener is fundamental for the elaboration of

poly(CDGE)/poly(Bz) IPNs. To this aim, the curing of CDGE with various diamine hardeners has

been investigated by DSC analysis, as well as the curing of the Bz monomer in presence of the

selected diamine.

2.1.2 Determination of the Bz monomer

As described previously, it is essential to control the competition reactions which may occur

between benzoxazines, epoxy and amine compounds in order to elaborate IPNs. For this reason,

the suitable conditions for the elaboration of IPN between CDGE and benzoxazines are studied in

the following chapter. A benzoxazine model molecule synthetized from phenol, ethylenediamine

and paraformaldehyde, (EDBz, Figure IV - 16) has been selected in order to avoid any likely

additional side-reaction from benzoxazines substituents or functional groups.

Figure IV - 16. Chemical structure of the EDBz model Bz monomer.

Miscibility tests were achieved between the CDGE and the EDBz compounds. The two compounds

were miscible and no demixion appeared even after several days.

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2.1.3 Determination of the suitable di-amine hardener

The choice of the diamine hardener used for the polymerization of the CDGE is essential for the

elaboration of IPNs. In order to avoid the formation of polymer co-networks, a diamine non-

reactive towards the EDBz monomer and allowing the curing of CDGE at low temperature will be

needed.

In order to find a suitable hardener for the epoxy system, various diamine compounds were

tested by the following procedure: The CDGE was heated at the EDBz monomer melting

temperature (Tm = 116 °C for EDBz). The amine hardener was then added to the mixture in

stoichiometric amount to the CDGE compound. The blend was stirred at Tm until a homogeneous

mixture was obtained. The reaction mixture was then studied in function of the temperature by

DSC analysis.

DSC thermograms of CDGE cured with different diamines are reported on Figure IV – 17. As a

comparison, the curing of the EDBz monomer is also reported.

Figure IV - 17. Curing conditions of CDGE with various diamine compounds monitored by DSC

analysis (N2, 20 K/min), compared to the curing conditions of the EDBz monomer (Dashed

curve, (N2, 20 K/min)).

Different curing behaviours, depending on the diamine hardener are observed by DSC analysis.

Even though the curing onset is situated around 50 °C, independently of the diamine hardener,

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the curing peaks width are differing. In the presence of diethylenetriamine (DTA) and m-

xylenediamine, the exothermic peaks are rather thin and ranging from 50 °C to around 150 °C. In

the case of isophorone diamine (IPD) as hardener, the exothermic peak is boarder ranging from

50 °C to around 175 °C. Finally, when Jeffamine EDR 148, trans-1, 4-diaminocyclohexane, or

Jeffamine EDR 176 are used as hardener, very broad exothermic peaks are observed ranging from

50 °C to over 200 °C, overlapping the ROP temperature of the EDBz monomer.

As we aim at finding an epoxy-amine system curing at low temperature, the DTA, m-

xylenediamine, and IPD hardener are the most suitable. Nevertheless, as described above, the

diamine hardener is added to the CDGE/EDBz mixture at elevated temperature (T > 116 °C). A

diamine hardener with a high boiling temperature is needed, in order to avoid any evaporation

during the addition step to preserve the stoichiometric amount between the diamine compound

and CDGE. DTA and DAC display the lowest boiling temperatures: Tb = 199 – 209 °C and Tb = 197

°C respectively. In consequence, the isophorone diamine (IPD; Tb = 247 °C) appears as the most

suitable hardener for CDGE in the elaboration of IPNs.

In order to confirm the suitability of IPD as hardener for the elaboration of IPNs, the curing of the

EDBz monomer was monitored by DSC in the presence of one equivalent of diamine hardener

(data not showed). The DSC analysis corresponding to the curing of EDBz in presence of IPD

evidenced the absence of exothermic peak in the range from 0 °C to 200 °C, indicating that the

EDBz monomer did not react with IPD within this temperature range. Only an exothermic peak

starting around 200 °C can be observed, probably corresponding to the EDBz ring opening. In

conclusion, the DSC monitoring of the EDBz curing in presence of IPD confirms that IPD could be

a suitable hardener of the CDGE network without reacting with EDBz at rather low temperature

and furthermore without influencing on the EDBz ROP at elevated temperature.

These preliminary results were further confirmed by the DSC analysis of the CDGE/IPD/EDBz

ternary system (Figure IV - 18). The DSC analysis of the ternary system curing was then

compared to the curing of the reference network CDGE/IPD and the curing of EDBz respectively.

The particular case of an expected IPN in 60 wt% CDGE and 40 wt% EDBz (named CDGE/EDBz

60/40) was chosen for the DSC monitoring. The IPD hardener was added in stoichiometric ratio

to CDGE.

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Figure IV - 18. Curing conditions of various systems a) CDGE with IPD, b) EDBz and c) 60/40

CDGE/EDBz with IPD monitored by DSC analysis (N2, 20 K/min).

The DSC thermogram of the CDGE/EDBz system, displayed on Figure IV - 18, indicates the

possible formation of IPNs between CDGE and EDBz. Indeed, when comparing the thermograms

of CDGE and EDBz, it can be observed that the formation of the two networks can be

differentiated. The formation of the neat poly(CDGE) network with IPD (Figure IV - 18, a) occurs

at rather low temperature, as an exothermic peak is displayed in the range of 50 °C to 170 °C. The

formation of the neat poly(EDBz) network (Figure IV - 18, b) occurs at elevated temperature,

indicated by the presence of an exothermic peak corresponding to the EDBz ROP starting around

200 °C. Finally, the DSC thermogram of the ternary system (CDGE/IPD/EDBz) (Figure IV - 18, c)

confirms the formation of sequential networks. Indeed, a first exotherm is observed from 50 °C

to 200 °C, corresponding to the polymerization between CDGE and IPD, followed by a second

exotherm observed from 200 °C to 250 °C, corresponding to the EDBz ROP. In consequence, the

elaboration of an IPN structure can be assumed according to this DSC monitoring.

In conclusion, the formation of the first poly(CDGE) network by reaction between CDGE and IPD

should be achieve at low temperature, followed by the formation of the second poly(EDBz)

network at high temperature. By default, the CDGE monomer will always be reacted with IPD in

stoichiometric ratio. Consequently, in the following paragraphs, in order to facilitate the materials

denomination, the CDGE/IPD system will be noted CDGE (unreacted mixture of CDGE and IPD)

and the crosslinked network will be noted poly(CDGE) (crosslinked CDGE/IPD network).

Similarly, crosslinked network issued from EDBz will be noted poly(EDBz).

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2.2 Curing profile for the elaboration of poly(CDGE)/poly(EDBz) IPNs

To insure the successive elaboration of the two networks, a multiple step curing profile was

applied to the monomers mixtures. The model case of a 60/40 (CDGE/EDBz) system was also

used for this study. First, the elaboration at low temperature of the poly(CDGE) network is

favoured, resulting in a first step cure at 100 °C during 16h. The temperature of 100 °C is chosen

with the aim to allow the epoxy-amine polymerization. Furthermore, the CDGE compound plays

the role of a solvent for EDBz and a temperature of 100 °C is sufficient to keep the EDBz compound

in a molten state. The curing of the EDBz monomer is then triggered at moderate temperature by

a first cure at T = 160 °C during 1h followed by 2h at T = 180 °C, in order to avoid a too rapid

gelation of the system. The post-cure of the poly(EDBz) network is finally achieved after 2h at

200 °C and 30 min at 220 °C (Figure IV - 19).

Figure IV - 19. Curing conditions of CDGE/EDBz (60/40 % wt) systems.

The successive formation of the networks can be demonstrated by quenching the curing at the

assumed end of the poly(CDGE) network formation, i.e. after 16 h at 100 °C. DSC analysis of the

partially (i.e. after 16 h at 100 °C) and of the totally cured poly(CDGE)/poly(EDBz) (60/40)

system (at the end of the thermal treatment) were carried out to confirm the sequential network

formation and their total cross-linking. To further validate the curing conditions, soluble fractions

of the samples were extracted with chloroform after the first curing step and on the final material.

The DSC analysis and the solvent extraction were achieved in order to estimate the amount of

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unreacted CDGE or EDBz monomers. The extracted content (EC) was given as a weight

percentage:

EC (%) = (𝑊𝑖−𝑊𝑒)

𝑊𝑖 x 100

Where 𝑊𝑖 and 𝑊𝑒 are the weights of the samples before and after extraction, respectively.

2.2.1 First step curing

2.2.1.1 Evaluation of the poly(CDGE) formation

The DSC of the poly(CDGE) reference material, without EDBz, after the first cure of 16 h at 100

°C, is displayed in Figure IV - 20.

Figure IV - 20. DSC analysis (N2, 20 K/min) of the poly(CDGE) material (without EDBz) after the

first curing step of 16 h at 100 °C.

The thermogram of the poly(CDGE) network, without the EDBz monomer,after the first curing

step at 100 °C during 16 h, displays a slight exothermic peak around 175 °C, indicating that the

CDGE curing is probably not entirely achieved. The enthalpy of ΔH = 2.5 J/g indicates that a minor

amount of CDGE has not polymerized after the first curing step when comparing to the

polymerization enthalpy needed to fully cure the system (ΔH = 112.8 J/g). The reaction progress

is thus estimated to be achieved at 98 %. This result is comforted by the low extractible content

of 7 ± 5 % after solvent extraction in CHCl3. In conclusion, the poly(CDGE) network is almost

achieved after 16 h at 100 °C, and the low enthalpy and the low extractible content were

considered as very acceptable for the IPNs elaboration conditions.

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2.2.1.2 Evaluation of poly(EDBz) formation

The CDGE system was then crosslinked in presence of EDBz monomer in order to verify that EDBz

does not interact in the formation of the poly(CDGE) network. The corresponding DSC

thermogram after the first curing step of 16 h at 100 °C is displayed in Figure IV - 21.

Figure IV - 21. DSC analysis (N2, 20 K/min) of the poly(CDGE)/EDBz (60/40) system after the

first curing step of 16 h at 100 °C, and compared to neat poly(CDGE) after 16 h at 100 °C.

As expected, the DSC thermogram of the poly(CDGE)/EDBz (60/40) system displays an

exothermic peak starting around 175 °C, corresponding to the ROP of the EDBz monomers. This

peak confirms that un-reacted EDBz monomers are present in the material after the first curing

step. The formation of the poly(EDBz) network will thus be achievable since it has still not

reacted. These results are corroborated by the enthalpy of ΔH = 17.2 J/g of EDBz, very close to

the polymerization enthalpy of the single EDBz network (ΔH = 17.9 J/g of EDBz). Furthermore,

no exothermic peak relative to the CDGE polymerization reaction is visible, further confirming

the formation of a first poly(CDGE) network during the first curing step, without involving the

EDBz monomers. These results were further confirmed by the extractible content obtained for

the poly(CDGE)/EDBz (60/40) system after the first curing step. Indeed, 38.5 ± 5 % of extractible

content were obtained after 72 h solvent extraction in CHCl3, confirming that almost all the EDBz

monomers remain unreacted during this first curing step as 40 wt% of EDBz are present in the

starting system.

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2.2.2 Full curing profile

Finally, DSC measurements and solvent extractions were performed (Figure IV - 22) on fully

cured poly(CDGE)/poly(EDBz) (60/40) material (curing program: 1 h at 160 °C, 2h at 180 °C, 2 h

at 200 °C and 30 min at 220 °C).

Figure IV - 22. DSC analysis (N2, 20 K/min) of the poly(CDGE)/poly(EDBz) (60/40) material

after the full curing program (1 h at 160 °C, 2 h at 180 °C, 2 h at 200 °C and 30 min at 220 °C).

As expected, no exothermic peaks are observed. This absence of exothermic peaks reveals the

total cure of both networks after the full curing program applied to the materials. Furthermore,

the 0 % extractible contents found for 60/40 poly(CDGE)/poly(EDBz) corroborate the DSC

results.

In conclusion, it can be deduced that the selected curing program is suitable for the elaboration

of IPN materials between CDGE and EDBz. The following part focuses on the CDGE/EDBz

monomers ratio onto the properties of the final materials.

2.3 Poly(CDGE)/poly(EDBz) IPNs

2.3.1 Poly(CDGE)/poly(EDBz) IPN Material elaboration

The reference materials from EDBz and CDGE, as well as the IPN materials with various

compositions, were elaborated by first mixing the CDGE compound and the EDBz compound at

100 °C and degasing during 1 h at 100 °C, followed by the addition of the IPD hardener in

stoichiometric ratio to the CDGE monomer. The mixtures were then transferred to a U-shaped

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mold. The previously determined curing program of 16 h at 100 °C, 1 h at 160 °C, 2 h at 180 °C, 2

h at 200 °C and 30 min at 220 °C was applied to each material.

IPNs with different EDBz contents ranging from 20 % to 80 % by weight were synthetized, while

keeping the same ratio between CDGE and the IPD hardener. All investigated CDGE/EDBz

compositions are reported in weight-by-weight ratio. Thus, an IPN obtained from a mixture of

0.80 g of CDGE and 0.20 g of EDBz will be noted as poly(CDGE)/poly(EDBz) (80/20) IPN.

2.3.2 Thermo-mechanical properties of IPN materials

The thermo-mechanical properties of poly(CDGE)/poly(EDBz) IPNs were studied by DMA

analysis and displayed on Figure IV - 23. For the sake of comparison, the two single networks

poly(EDBz) and poly(CDGE) were also elaborated using the same curing conditions and

characterized by DMA.

Figure IV - 23. Evolution of the storage modulus E’ of poly(CDGE)/poly(EDBz) IPNs (80/20,

70/30, 60/40, 50/50, 40/60, 30/70 and 20/80) as a function of temperature, obtained by DMA

(Tension mode with 0.05 % strain, 1 Hz and 3 °C/min).

The poly(CDGE) network is characterized by an α-relaxation centered at Tα = 50 °C and a storage

modulus in the glassy state about 400 MPa. The poly(EDBz) network is in a glassy state up to 150

°C with E’ around 6 to 7 GPa and displays a Tα of 216 °C (Figure IV – 23 and Figure IV – 24).

As far as IPN are concerned, all the IPN materials are in a glassy state below 50 °C, as observed on

the DMA curves of the poly(CDGE)/poly(EDBz) networks. With increasing the temperature from

50 °C to 175 °C, the storage modulus of the IPN materials decreased, which indicate the materials

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softening. Furthermore, the values of the storage moduli were strongly impacted by the IPN

composition. Indeed, in this temperature range, it can be observed that the storage modulus

increased with weight proportion of the EDBz compound (arrow in Figure IV - 23). For instance

at 150 °C, the storage modulus increases from 9 MPa to 1600 MPa for the 80/20 and 20/80 IPN

materials respectively (containing 20 % and 80 % weight proportion of EDBz respectively).

Above 180 °C the storage modulus of the various IPN materials decreases again due to the

mechanical relaxation of the poly(EDBz) rich phase. As expected, an improvement of the

poly(CDGE) network thermo-mechanical properties is observed when combining it with a

poly(EDBz) network in an IPN structure.

Thermomechanical properties give a picture of local dynamic of polymer chain. As described

above when the two kinds of polymer chains are in close vicinity their dynamic influence each

other which results in only one mechanichal relaxation at a unique Tα. Hence the IPN present no

phase separation at the DMA scale. In the present case, for three IPN compositions with high CDGE

content – 80/20, 70/30 and 60/40– only one transition can be observed (Figure IV- 24).

Figure IV - 24. Evolution of the storage modulus E’ and tanδ of poly(CDGE)/poly(EDBz) IPNs

(80/20, 70/30 and 60/40) as a function of temperature, obtained by DMA (tension mode with

0.05 % strain, 1 Hz and 3 °C/min).

A lone mechanical relaxation around 70 °C is observed for these materials, close to the mechanical

relaxation of single poly(CDGE) as it is the main component of those IPNs. As no additional

transition corresponding to a poly(EDBz) rich phase is observed at higher temperature, it can be

assumed that the poly(EDBz) is entangled at nanometer scale within the poly(CDGE) network.

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When comparing to the neat poly(CDGE) network, an increase of the materials storage modulus

and Tα were observed by DMA analysis. The 80/20, 70/30 and 60/40 poly(CDGE)/poly(EDBz)

materials could thus be determined as materials composed of the first formed poly(CDGE)

network probably reinforced by poly(EDBz) network.

Contrary to these three IPNs, two mechanical relaxations are observed for the other compositions

from 50/50 to 20/80, like it can be observed on the curves displaying the tanδ values versus the

temperature (Figure IV - 25). Phase separation, even if it is fairly limited, occurs. For each IPN

material, the first mechanical relaxation located around 40 to 50 °C is associated to the

poly(CDGE) phase relaxation, while the second relaxation situated around 200 to 220 °C

corresponds to the poly(EDBz) phase.

Figure IV - 25. Evolution of the tanδ of poly(CDGE)/poly(EDBz) IPNs (50/50, 40/60, 30/70 and

20/80) as a function of temperature, obtained by DMA (tension mode with 0.05% strain, 1Hz

and 3°C/min).

All the IPN materials ranging from 50/50 to 20/80 are displaying complex phase morphology, as

evidenced by two distinct mechanical relaxations. In order to determine the domains

structuration of the two polymer phase, mechanical model developed primarily for polymer

blend have been tentatively used.

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2.3.3 Estimation of the morphology by theoretical models

The determination of the IPN materials morphology is very important in order to relate it to the

materials properties. Despite several characterization attempts, particularly through AFM in

tapping mode or elementary EDX-SEM analysis, we remained unable to determine the

morphology of the poly(CDGE)/poly(EDBz) IPN materials when phase separation occured.

Consequently, with the aim to obtain an estimation of the materials morphology, a comparison

between the IPN materials experimental thermo-mechanical data and those of theoretical models

were achieved. Indeed, IPN can be multiphase systems for which the storage modulus obtained

by DMA can be correlated to their composition and morphology. Several theories have been

developed to this aim. Most of the theories consider a macroscopic isotropy of the systems and a

perfect adhesion between the different phases.

Kerner described a model for a matrix in which spherical inclusions are dispersed over the whole

composition range.241 As this model does not take into account the interactions between the

dispersed inclusions and the continuous matrix, it predicts accurately the polymers blend

properties when the volume of the dispersed phase is low.

The material shear modulus G is defined as follow:

𝐺

𝐺1 =

(1−ɸ2)𝐺1+(𝛼+ɸ2)𝐺2

(1+𝛼ɸ2)𝐺1+ 𝛼(1−ɸ2)𝐺2

Where 1 is the continuous phase and 2 is the dispersed spherical inclusions, G is the shear

modulus, ɸ2 is the volume fraction of the inclusion spheres, and α is a function of the matrix

Poisson ratio according to the following equation:

𝛼 =2(4 − 5𝜈)

(7 − 5𝜈)

Where ν is the Poisson’s ratio.

A model which predicts a phase inversion at middle-range composition was predicted by

Budiansky.242 In the first case, the material is formed by a continuous phase 1 in which a second

phase – 2 - is dispersed as long as the volume fraction ɸ2 of the second phase is lower than 0.5.

When ɸ2 is higher as 0.5, a phase inversion occurs and the phase 2 becomes continuous with

phase 1 being dispersed within it. For this model, the shear modulus G observes the following

equation:

ɸ1

1+ɛ(𝐺1𝐺

−1) +

ɸ2

1+ɛ(𝐺2𝐺

−1) = 1

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Where ɛ = 2(4−5𝜈)

15(1−𝜈) ,

and ν is the Poisson’s ratio of the blend calculated using a combination of mixing, G the shear

modulus, and ɸi is the volume fraction of each component polymers.

Unlike the two previous models, Davies reported a model taking into account the interactions

between the two polymer phases in which both phases are co-continuous over the whole

material.243 In this particular case, the shear modulus G is expressed as:

𝐺1/5 = ɸ1𝐺11/5 + ɸ2𝐺2

1/5

As a reminder, these three models have rather been developed for the mechanical properties of

polymer blends. Nevertheless, numerous authors report their use for the description of IPNs

viscoelastic properties.244, 245 These models were shown to give an idea of the materials

morphology.

The modulus values calculated from the three aforementioned models, as well as the

experimental data of the poly(CDGE)/poly(EDBz) IPN materials, are reported on the Figure IV -

26. The models and materials modulus are reported versus their EDBz volume content. The shear

moduli (G’) of the poly(CDGE)/poly(EDBz) IPN materials were determined by the E’ and tanδ data

measured by DMA analysis as follow:

𝐸 = 𝐸′

cos (𝛿)

and

𝐺′ =𝐸

2∗(1+𝜈)

As models assume mixing of a hard and a soft polymer, the values of E’ and tanδ were taken at

140°C (poly(CDGE) in elastic state and poly(EDBz) in glassy state). In consequence, the Poisson’s

coefficients of rubbery poly(CDGE) and glassy poly(EDBz) networks are equal to 0.50 and 0.33

respectively. The Poisson coefficient of the IPN materials is calculated as the volume average of

those of the both component, depending their composition by the following formula:

𝜈 = ((0.50 ∗ 𝐶𝐷𝐺𝐸 𝑣/𝑣%) + (0.33 ∗ 𝐸𝐷𝐵𝑧 𝑣/𝑣%))

The shear moduli of the IPN materials were then compared to the calculated values obtained by

the three models.

It is important to notice that the models are employed for materials which display two transitions

on their DMA analysis as it is the case for poly(CDGE)/poly(EDBz) IPN with compositions ranging

from 50/50 to 20/80. Nevertheless, in the present case, for three IPN compositions with high

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CDGE content – 80/20, 70/30 and 60/40 – only one transition can be observed (Figure IV- 26)

and they will therefore not be discussed in relation to the models.

Figure IV - 26. Shear modulus of poly(CDGE)/poly(EDBz) IPN materials versus EDBz volume

fraction compared with modulus-composition models.

As it can be observed on the Figure IV - 26, the IPN shear moduli correlates closely the Davies or

Budiansky model for the IPNs from 50/50 to 20/80. Furthermore, the morphology of the IPN

materials is directed by the chemistry reactions that are occurring during the IPN elaboration.

Indeed, the first formed network is necessarly continuous.246 The poly(CDGE) network is thus

continuous. This is not in accordance with the Budiansky model whereas it is with Davies model

that consideres the second formed network as also continuous. Therefore, the IPNs of the studied

range could thus be considered as two co-continuous phases. Therefore, poly(CDGE)/poly(EDBz)

IPNs whether they are homogeneous at the DMA scale or co-continuous phase separated have

mechanical properties that are averaged by the volume proportion of polymers. The IPN

morphology is adequate for combination of both polymer properties, i.e. PBz network should

efficiently prevent the water diffusion, in addition of clear reinforcement of the thermal and

mechanical properties of the materials, whatever their composition.

2.3.4 Behaviour toward water exposure

In order to verify that the introduction of poly(EDBz) in IPNs is a viable strategy to prevent the

water diffusion within the material, swelling tests were achieved and monitored by DSC analyses.

The poly(CDGE)/poly(EDBz) IPN materials – varying from 80/20 to 20/80 in ratio – as well as

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the poly(CDGE) and poly(EDBz) single network were swollen in water during 15 days at 80 °C. It

was not possible to estimate the amount of water uptake from simple weight measurements

because the weight of the swollen samples was to low and the uncertainty of the measures were

thus to high. In consequence, the swelling behaviour of the materials was determined from the

melting enthalpy of water trapped in the material by DSC analysis. The melting point depression

study was followed in the present case. The heating of the swollen materials from -50 °C to 20 °C

at 5 k/min was observed.

The DSC curves during heating of the water swollen IPN materials and single networks are

displayed in Figure IV - 27.

Figure IV - 27. DSC thermograms of poly(CDGE)/poly(EDBz) IPNs (80/20, 70/30, 60/40,

50/50, 40/60, 30/70 and 20/80) and poly(CDGE) and poly(EDBz), during the heating of

swollen materials (N2, 5 K/min).

First of all, it is important to notice that depending on the IPN composition, different phase

transitions were observed. No endothermic peak is observed on the DSC curve relative to water

melting in the single poly(EDBz) network. Indeed, PBz resins are well-known for their very low

water uptake.120 On the contrary, the poly(CDGE) epoxy network was reported to display a high

water uptake, as verified by the presence of a bulk-water melting endothermic peak around 0 °C

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(ΔH = 27.31 J/g). When adding EDBz to the poly(CDGE) network a clear evolution can be

observed. A second endothermic peak shifted to around -10 °C is readily observed. The following

attribution of the endothermic peaks were hypothetized based on the work related by Wirtz et

al..247 The transition at higher temperature (around 0 °C) is related to the melting of the bulk

water contained in pores or cavities of the materials. The melting endotherm at lower

temperature (around -15 to -10 °C) represents the phase transition of the water confined in the

poly(CDGE) network, as water can form hydrogen-bonds with hydrophilic groups of such a

polymer.248

It corresponds to a confined water melting endotherm, and seems to be related to the presence

of poly(EDBz) network. A fraction of trapped water in close vicinity of polymer chains does not

behave as bulk water, propably beacause of reduced water domain’s size. It is furthermore

important to notice that with increasing amount of poly(EDBz) resin, the enthalpy of the

endothermic peak around 0 °C, attributed as the bulk-water melting peak, is varying from ΔH =

27.31 J/g (poly(EDBz) = 0 wt %) to ΔH = 0.22 J/g (poly(EDBz) = 40 wt %). In addition, the

enthalpy of the endothermic peak around -10 °C is also decreasing with increasing amount of

poly(EDBz). A threshold is reached at 40 wt % of poly(EDBz). Indeed, melting enthalpy at -10°C

related to confined-water becomes higher then that the melting enthalpy of bulk-water at 0°C.

IPN water uptake allows probing the IPN hydrophobicity since above 40 wt % of poly(EDBz) in

the IPN almost no bulk-water domains are anymore detected and the absorbed water molecules

are confined with the polymer chain and decreases gradually as the amount of poly(EDBz) within

the IPN increases. As a result, the global water uptake of the IPN materials is deacreasing with

increasing amount of EDBz.

In conclusion, the introduction of poly(EDBz) network within the poly(CDGE) network reduces

the water uptake of poly(CDGE) with increasing amount of poly(EDBz), while improving their

thermo-mechanical properties. Furthermore, an unexpected behaviour was also observed.

Indeed, PBz networks are known to have very low water uptake, but it seems that by the

elaboration of IPNs with the poly(CDGE) network, the PBz based IPN could be able to be swollen,

which could be an interesting application of these new IPNs. Nevertheless, further

characterizations are needed in order to confirm the observed results.

3 Conclusion

Diglycidyl ether of cardanol (CDGE) is a difunctionnal epoxy molecule that could interestingly and

advantageously substitute diglycidyl ether of BPA (BADGE) in applications such as coatings.

Indeed, CDGE has better adhesion properties than BADGE in addition to its non-carcinogenic

properties compared to BADGE. However, CDGE suffers from a relatively high swelling in water -

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due to its very low cross-linking density- , and is thus not suitable for almost all the coatings

applications. A way to tackle this issue is to reinforce at the macromolecular scale by the

formation of interpenetrating polymer networks (IPN) with polybenzoxazine.

The aim of the chapter was to prove the feasibility of the elaboration of IPNs between the

poly(CDGE) and the poly(EDBz) networks. Many chemical reactions can compete during the

formation of such a material, since benzoxazine monomers are able to react both with epoxies

and with hardeners used to commonly crosslink epoxies. Among the long list of tested diamines

isophorone diamine (IPD) appears to be a very good candidate. Indeed, in CDGE/EDBZ mixtures,

IPD only reacts with CDGE when moderate curing conditions are applied (100 °C during 16

hours). DSC measurements and solvent extractions in chloroform evidenced that 97 % of EDBZ

did not react during this first step and can thus still be interpenetrated within poly(CDGE) after a

second thermal treatment at higher temperature (1h at 160 °C, 2 h at 180 °C, 2 h at 200 °C and 30

min at 220 °C).

Compositions of the IPN were adjusted by screening the ratio between EDBZ and CDGE. DMA

characterizations highlight the formation of IPN for the 80/20, 70/30 and 60/40 compositions as

a lone Tg is observed (76.6 °C, 72.7 °C and 71.8 °C, respectively). As expected, storage moduli

increase while increasing the content of EDBZ, from 400 MPa for neat CDGE, 9000 MPa for 50/50

materials and about 13000 MPa for 20/80 materials, for instance (T = 25 °C).

Theoretical models were used to identify the morphology of the two phases IPN. These theories

are based on the evolution of the storage moduli of the materials as a function of their

composition. Experiment fits in very high accordance to the Davies model. According to this

theoretical model and to the occurring chemistry reactions, a co-continuous matrix should be

obtained for the systems with EDBz content above to 50 %. In spite of numerous attempts (atomic

force microscopy, scanning electron microscopy), it was not possible to observe these

morphologies and up to now the viability of this model is not confirmed.

Finally, swelling tests in water at 80 °C were performed on all the set of materials (i.e. with EDBz

content ranging from 0 to 100 wt %). Interestingly, it was observed that the incorporation of

poly(EDBz) leads to a significant drop of the swelling of poly(CDGE) in water. Evolutions of the

melting enthalpies of water were recorded on the swollen samples by differential scanning

measurements, as this method is very sensitive. Two endotherms of melting were observed at 0

°C and -10 °C depending on the materials composition, corresponding respectively to bulk- and

confined-water within the networks. In neat poly(CDGE) networks, water molecules are free,

with a melting enthalpy of 27.31 J/g. Increasing poly(EDBz) content leads to a confinement of the

water molecules, and to a decrease of the total melting enthalpy.

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In conclusion, it was demonstrated in this chapter that obtained IPN from CDGE and EDBZ is

possible through a suitable choice of the diamine hardener and of the curing conditions. Materials

with interesting properties were obtained, as their behaviour toward water is highly affected by

the poly(EDBz) content. These results were just obtained with a model – simple- benzoxazine

monomer to prove the feasibility of the concept. As it was shown in the third chapter, the chemical

design of benzoxazine monomers is versatile, and it could be easily envisioned that other

molecular architecture could be built by using other Bz monomers. Clearly, asymmetric

monomers with a cardanol moiety could be a major tool to tailor the morphology and properties

of the resulting IPN.

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General Conclusion and Perspectives

As mentioned all along the manuscript, the development of polymeric materials from natural and

renewable resources has attracted tremendous concern. Among the large variety of biomass-

derived compounds, cardanol through its inherent properties, has attracted our attention.

Throughout this thesis we have studied the potential of using cardanol as versatile chemical

platform to conduct different chemical transformation with the aim to find high add-value

applications for this underutilized product. We particularly focused in all our studies on the

control of the materials properties by the tuning of their chemical structures.

The first study described in this manuscript was the development of three cardanol-based

ammonium surfactants, and their potential as oraganomodifier for clays to enhance the

dispersion in composite materials. A particular focus was given to the reactivity of these

surfactants toward Monmorillonite clay (MMT) and epoxy resin. Three surfactants bearing

different amine reactive functionalities were obtained. The organomodification by cationic

exchange of MMT layers was effective using the three cardanol-based surfactants as evidenced

by XRD and MALDI-TOF/MS analyses. The increased interlayer distances between the clay

platelets were however found to be roughly similar due to the close chemical structure of the

surfactants. After the exfoliation, the content of amine functionality availlable (able to further

react with epoxy groups) of each surfactant was verified by grafting of furfuryl glycidyl ether and

further quantified by MALDI-TOF/MS analysis. Clay mineral-based polymer (CPN) with

conventional diglycidyl ether of bisphenol A were then prepared with the three O-MMT. As

expected, The XRD analysis and SEM observations coupled with energy dispersive X-ray analyses

revealed that the surfactant reactivity towards epoxies influences the clay dispersion. Indeed, for

the clay modified by the surfactants with lower available amine functionalities, only an

intercalated structure could be evidenced. Oppositely, the exfoliation of the clay layers was clearly

favoured by the clay modified by the surfactant displaying the higher content of amine

functionality as no diffraction peak could be observed on the corresponding XRD diffractogram.

In the chapter 3 we highlighted in a first stage the synthesis and characterization of PBz materials

from bio-based di-Bz monomers. Yet, the potential of PBz material from di-vanillin Bz monomer

was very limited because of its early thermal degradation (before melting) and its high melting

temperature. In the case of di-cardanol Bz monomer, the corresponding material is an easily

processable thermoplastic material that was poorly crosslinked and started creeping around 100

°C. In order to obtain an easily processable bio-based Bz monomer and with the aim to combine

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the good thermal properties of vanillin-based Bzs and the low melting temperature of the

cardanol-based Bz monomer, we reported an efficient preparation of asymmetric bio-based di-

benzoxazines (named Vani-Card) via a two-steps synthesis pathway including a controlled mono-

substitution of cardanol-based benzoxazines followed by a coupling with vanillin. Such

combination resulted in a bio-based Bz monomer displaying a large processing window and high

thermal stability (Above polymerization temperature). The reactivity of this monomer was also

clearly enhanced in comparison to di-cardanol monomer as highlighted by rheology analyses. In-

depth characterization of the thermoset material resulting from asymmetric Vani-Card Bz

displayed very comparable thermal and mechanical properties to other known PBzs either

partially or fully based on renewable compounds. Finally the presence of the cardanol moiety was

shown to strongly improve the thermal stability of the PBz material as evidenced by TGA analysis.

This versatile approach is thus a powerful tool to access a wide range of asymmetric bio-based

benzoxazines given the large number of precursors available and their possible combination. It

paves the way toward easily processable high performance bio-based benzoxazines.

Finally, in the last chapter, we studied the macromolecular reinforcement of a diglycidyl ether of

cardanol (CDGE) based network. To this end, a poly(CDGE) network was combined through the

formation of interpenetrating polymer networks (IPNs) with a polybenzoxazine network

(poly(EDBz)). Since benzoxazine monomers are able to react not only with epoxies but also with

their diamine hardeners, an appropriate scrutiny of reactant systems and optimal curing

conditions was done. The elaboration of an poly(CDGE)/poly(EDBz) IPN structure was found to

be favoured by an in-situ sequential IPN synthesis. The first poly(CDGE) network can be

synthetized in a first curing step by polymerization of CDGE with isophorone diamine as hardener

at low temperature without interactions with the EDBz monomers present in the system. The

second poly(EDBz) network can then be synthetized by homopolymerization of the EDBz

monomers at higher temperatures. The properties of the poly(CDGE)/poly(EDBz) materials were

then studied in function of their compositions. As expected, DMA characterization highlighted an

increase of Tg and elastic moduli of the materials while increasing content of EDBz. The IPN

materials morphology was estimated by comparison to experimental models based on the

evolution of the storage moduli of the materials as a function of their composition. Our

experimental findings fit at very high accordance to the Davies model, tending to a co-continuous

system. Nevertheless, in spite of numerous attempts (atomic force microscopy, scanning electron

microscopy), it was not possible to observe these morphologies and up to now the viability of this

model is not confirmed. Finally, it was observed by swelling testing that the incorporation of

poly(EDBz) leads to a significant drop of the swelling of poly(CDGE) in water. In conclusion, the

179

feasibility of the concept of the elaboration of IPN from CDGE and EDBZ in order to reinforce the

poly(CDGE) network was achieved in this work.

In conclusion the various studies described in this manuscript highlighted the possibility of using

cardanol as a bio-based and very versatile building block for the elaboration of diverse materials

including bio-based thermoset materials (polybenzoxazines and epoxies), but also as a

component for the elaboration of composite materials. Indeed, in chapter II cardanol-based bio-

based surfactants were used to elaborate clay-epoxy nanocomposite materials. We could

conceive of applying this strategy for the reinforcement of bio-based polybenzoxazine materials

for example. Moreover, as described in the chapter III, we managed to elaborate a cardanol- and

vanillin-based polybenzoxazine material displaying good properties. In order to further enhance

those properties, we could elaborate bio-based polybenzoxazine-clay nanocomposite materials

using cardanol-based surfactants as clay organomodifiers. Nevertheless, the high performances

of PBz materials were strongly related to the formation of an H-bond network. In order to study

the interaction between pristine clay and PBz resins, prior to clay organomodification, we

proposed to study the supramolecular interactions between kaolin and poly(EDBz).149 The

thermal and thermo-mechanical properties of the benzoxazine resins were significantly

improved.

Finally, in chapter IV we described the improvement of the cardanol-based epoxy network

(poly(CDGE)) by the formation of IPN materials with poly(EDBz). Still, in order to improve the

properties of poly(CDGE), one can envision for example to tune the structural features of the bio-

based Bz varying the substituting groups. Indeed, the various functionalities on the bio-based

phenolic compounds would allow tailoring the PBz materials properties, as evidence by the effect

of the aldehyde function on vanillin for example. In consequence, it could be conceived to further

improve the poly(CDGE) material properties by various PBz resins bearing various functional

groups. To this aim, the strategy of synthetizing assymetric bio-based Bz monomers from

different bio-based phenolic compounds reported in chapter III could be considered.

180

Annex: Materials and Methods

1 Chapter II: Surfactants from cardanol

1.1 Materials

Epoxy derivative of cardanol (commercial grade NC513) was kindly supplied by Cardolite.

Montmorillonite (commercial grade N116 – Cation Exchange Capacity CEC = 116 meq/100g) was

obtained from Southern Clay. Tris(2-aminoethyl)amine (TAEA) and N,N-

dimethylethylenediamine (DMEDA) were purchased from Acros and used as received without

any purification. Ethylene diamine (EDA), 1,2-diaminocyclohexane (DAC, mixture of isomers),

Bisphenol A diglycidyl ether (BADGE) and the solvents used for the synthesis of the surfactants

were all purchased from Aldrich and used as received without any purification.

1.2 Characterization methods

1.2.1 NMR analysis

The 1H nuclear magnetic resonance (NMR) characterization was performed on a Avance 400

spectrometer (Bruker Biospin, Wissembourg, France) equipped with a 9.4 T Ascend magnet,

operating at a proton frequency of 400 MHz. Samples were dissolved in CDCl3 with all peaks

referenced relative to tetramethylsilane.

1.2.2 Mass analysis

Matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS) experiments were

recorded using a Bruker Autoflex III mass spectrometer (Bruker Daltonics, Leipzig, Germany)

equipped with a frequency-trippled Nd-YAG laser (ƛ = 355 nm) operating at a pulse rate of 50 Hz.

For MALDI analyses, samples were submitted to a solvent-free preparation, consisting of grinding

the matrix together with the analyte with a mortar and a pestle. The matrix/analyte mass ratio

was optimized for each sample, around 1/10 appearing to be a quite universal ratio for the clay

mineral samples, while a 50/1 ratio being a routinely used for the organic analytes such as

cardanol-based surfactants. Trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-

propenylidene]malononitrile (DCTB) was used for the analysis of surfactants and clays (no salt,

to detect species protonated prior to the LASER irradiation), α-cyano 4-hydroxycinnamic acid

(CHCA) was only used for the surfactants (no salt, to promote the protonation of the amine

groups).

181

1.2.3 XRD analysis

Wide-angle X-ray scattering (WAXS) experiments were conducted by means of an X’Pert Pro MPD

diffractometer from PANalytical, with a copper Kα radiation (1.54 Å) generated at 45 kV and 40

mA in transmission mode. Scans were recorded from 1.5 ° to 30 °, step size 0.02 ° at 5 °/min

scanning rate.

1.2.4 SEM analyis

Scanning electron microscopy (SEM) analyses were performed using a QUANTA FEG 200 from

FEI in the low vacuum mode (with water vapor as chamber gas). Chemical contrast analyses were

performed with a Gaseous Analytical Detector (GDA) for low magnitude observations.

Topographic micrographs were recorded with a secondary electron detector (SE), the chemical

contrast micrographs with a backscattered electron detector (BSE) and local elemental analysis

performed by Energy dispersive X-ray spectroscopy (EDS). Samples were prepared by cryogenic

fracture.

1.2.5 DSC analysis

Differential scanning calorimetry (DSC) thermograms were recorded by means of a Netzsch DSC

204 F1 Phoenix apparatus operating at inert atmosphere (nitrogen) with a linear heating ramp

from 20 to 250 °C at 20 °C/min rate.

1.3 Surfactant synthesis

1.3.1 Synthesis and purification of CardS1

Typically 5 g (14 mmol) of NC-513 in 100 mL CHCl3 were added to 6 g (41 mmol) of TAEA in 10

mL CHCl3. The mixture was heated at reflux for 20 h; the consumption of NC-513 was followed by

TLC, indicating reaction completion.

The excess of amine was removed by one solvent extraction with NaOH in water (50 mg/L). The

organic phase was dried using K2CO3 and evaporated. Viscous orange oil was obtained.

1H NMR (CDCl3, 400 MHz, 298 K): δ (ppm) (s, assignment, experimental integration, theoretical

integration). δ = 0.91 (m, CH3 from alkyl chain, exp 1.8 H, th 1.7 H), 1.31 (m, -CH2 from alkyl chain,

exp 13.5 H, th 13.6 H), 1.59 (t, -CH2-Ar, exp 2.3 H, th 2 H), 2.04 (m, -CH2*=CH-, exp 3.4 H, th 3.1 H),

2.28-2.95 (m, -CH2- from amine moiety and =CH-CH2*-CH= from Cardanol, exp 15.6 H, th 16.1 H),

3.04 (s, -NH2, exp 4.3 H, th 4 H), 3.84-4.23 (m, H α oxygen atoms, exp 3.5 H, th 3 H), 4.93-5.90 (m,-

CH= from alkyl chain, exp 4.8 H, th 4.5 H), 6.68-7.21 (m, H-Ar, exp 4 H, th 4 H).

182

MALDI-MS. CHCA Matrix: Detected m/z, Elemental Composition, Assignment. m/z

501.42/503.43/505.45, C30H53/55/57N4O2+, [M (n=3/2/1) + H]+.


Synthesis of CardS2 is similar to the CardS1 synthesis. 10 g (28 mmol) NC-513 in 100 mL CHCl3

were added to 5 g (84 mmol) of EDA in 20 mL CHCl3. The excess amine was removed by two

solvent extractions in brine. The organic phase was dried over K2CO3 and evaporated. Viscous

yellow oil was obtained.





3.18 (s, -NH2, exp 2.5 H, th 2H), 3.86-4.30 (m, H α oxygen atoms, exp 3.4 H, th 3 H), 4.90-5.93 (m,-

CH= from alkyl chain, exp 4.7 H, th 4.5 H), 6.64-7.25 (m, H-Ar, exp 4 H, th 4 H).


443.36/445.38/447.39, C28H47/49/51N2O2+, [M (n=3/2/1) + H]+.


The synthesis of CardS3 was performed as the previous ones by adding 10 g (28 mmol) NC-513

in 100 mL CHCl3 to 7.40 g (84 mmol) of DMEDA in 20 mL CHCl3. After reaction completion the

solvent was evaporated, and crude CardS3 was dissolved in ethyl acetate. Two extractions in

brine were carried out, and the organic phase was dried with K2CO3, filtered and evaporated.

Viscous yellow oil was obtained.





3.86-4.30 (m, H α oxygen atoms, exp 3.4 H, th 3 H), 4.90-5.93 (m,-CH= from alkyl chain, exp 4.9 H,

th 4.5 H), 6.64-7.25 (m, H-Ar, exp 4 H, th 4 H).


415.33/417.35/419.36, C26H43/45/47N2O2+, [M (n=3/2/1) + H]+.

183

1.4 MMT clay organomodification

Standard cation exchange procedures were employed for the preparation of organomodified

MMT (O-MMT).

Typical procedure it used to modify 1 g of clay consist in dissolving 1.12 g of CardS1 (2 equivalents

to MMT’s CEC) in 50 mL of EtOH at 80 °C. 20 mL of HCl solution in EtOH (0.1 M) were added to

protonate CardS1 to CardS1H+. The resulting solution was then added to the MMT/water

dispersion (100 mL water for 1 g of MMT) and the final mixture heated to 80 °C. The cation

exchange reaction was maintained for 16 hours at 80 °C under intensive magnetic stirring.

The O-MMT was filtrated and washed with 80 °C heated ethanol/water solution (50/50), until no

traces of Cl- could be detected with AgNO3. O-MMT are noted CardS1-MMT, CardS2-MMT and

CardS3-MMT.

1.5 Reaction of the intercalated surfactants with Fge

Furfuryl glycidyl ether (Fge) was used to evidence the residual reactivity of the surfactants

intercalated in O-MMT. Two drops of Fge were added to the dispersed O-MMT in CH2Cl2. The

mixtures were maintained under magnetic stirring for 8 hours at room temperature, and were

then filtered and dried at room temperature. The characterization of Fge-grafted surfactants was

done by MALDI- TOF/MS analysis.

1.6 Clay mineral-based polymer nanocomposite (CPN) preparation

10 mass% Clay/BADGE were prepared by mixing BADGE to O-MMT at 80 °C under vacuum during

1 hour. 1 epoxy-equivalent of DAC (1,2-diaminocyclohexane as the amine hardener) was then

added. The mixture was immediately transferred in a high-temperature silicone mold. The

thermal treatment was 2 h at 160 °C, followed by a post-cure at 190 °C during 2 h. The resulting

materials were characterized by X-ray diffraction and scanning electron microscopy.

2 Chapter III: Benzoxazines from cardanol

2.1 Materials

Cardanol (Ultralite 2023) was supplied by Cardolite. Ethylenediamine, paraformaldehyde,

vanillin, and the solvents were all purchased from Aldrich and used as received without any

purification.

184


2.2.1 NMR analysis

1H NMR spectra were performed on a Brucker Avance 400 spectrometer equipped with a 9.4 T

Ascent magnet, operating at a proton frequency of 400 MHz. Monomers were dissolved in

deuterated chloroform with all peaks referenced relative to tetramethylsilane (TMS). In regard

to the integration of the NMR signals, the precise integration depends obviously on the

composition of cardanol and related proportion of different isomers. The integrations are usually

calculated by moderation based on the abundance of unsaturation described in the literature.11,

51, 204-206 These unsaturation abundances can slightly vary regarding the origin and the processing

of raw Cardanol extracted from CNSL. As such the integration may diverge from sample to other.

The unsaturations abundances of the used cardanol were considered as follow in our calculations:

tri-unsaturated (n=3) ~ 41%, di-unsaturated (n=2) ~ 23%, mono-saturated (n=1) ~ 34%,

saturated (n=0) ~ 3%. In addition, the difference of relaxation times between aromatic and

aliphatic hydrogen may complicate the accurate quantification of all protons. Therefore, the peaks

related to the aliphatic chain of cardanol were integrated to the aliphatic hydrogen in β position

of the cardanol aromatic ring, which should integrate for 2H whereas the peak from -OCH3

function on the vanillin compound that should integrate for 3H, was used as reference for all other

peaks including those related to the benzoxazine structure.

2.2.2 Mass analysis

Molecular characterizations were also performed by high-resolution mass spectrometry (HR-

MS), using a LTQ/Orbitrap Elite (Thermo Scientific) equipped with an atmospheric-pressure

matrix-assisted laser desorption/ionization source (AP-MALDI PDF+, Masstech). This analytical

setup allows for the investigation of MALDI-produced ions using accurate mass measurement

(sub-ppm relative error) and structural confirmation by MSn. Samples were submitted to a

solvent-free preparation. α-Cyano-4-hydroxycinnamic acid (CHCA) was used for the analysis of

the benzoxazine monomers, and used as received from Sigma-Aldrich (St Louis, MO).

2.2.3 DSC analysis



from 20 to 250 °C at 20 °C/min rate. Thermo-gravimetric analysis (TGA) was performed on a

Netzsch TG 409 PC Luxx device operating in synthetic air (nitrogen: 80 mL/min and oxygen: 20

mL/min) with heating ramp from ambient temperature to 250 °C.

185

2.2.4 Rheology analysis

Rheo-kinetic measurements were performed with an Anton Paar Physica MCR 301 rheometer

equipped with a CDT 450 temperature control device with plate-plate (diameter 25 mm, measure

gap 0.5 mm) geometry. The polymerization measurements were recorded in oscillation mode at

an imposed 1 % deformation at 1 Hz frequency at 190 °C.

2.2.5 DMA analysis

Dynamic mechanical analyses (DMA) were carried out on bar samples (5x10x0.5 mm3) with a

Q800 model (TA instruments) operating in tension mode (strain between 0.05 and 0.07 %;

pretension, 10-2 N) at 1 Hz with a heating rate of 3 °C/min from ambient temperature to 250 °C.

2.2.6 TGA analysis

Thermo-gravimetric analysis (TGA) was performed on a Netzsch TG 409 PC Luxx device

operating in synthetic air (nitrogen: 80 mL/min and oxygen: 20 mL/min) with heating ramp from

ambient temperature to 250 °C.

2.3 Synthesis of the Bz monomers

2.3.1 Synthesis of the di-cardanol Bz monomer

Cardanol (5.96 g, 20 mmol, 2 eq) was reacted with EDA (0.60 g, 10 mmol, 1 eq), and

paraformaldehyde (1.27 g, 40 mmol, 4 eq) in CHCl3 at 70 °C for 48 h. The crude reaction was

washed three times with 1 M NaOH solution to remove unreacted phenolics and/or formed

oligomers, and the chloroform phase was neutralized by three washings with distilled water. The

solvent was removed under vacuum and the product was purified over column chromatography

(Heptane/Ethyl acetate = 7/3) to yield a white wax.

1H NMR (CDCl3, 400 MHz, 298 K) δ = 0.86-0.94 (-CH3 from cardanol alkyl chain, exp 4.08 H, th 3.54

H), 1.23-1.43 (-CH2 from cardanol alkyl chain, exp 27.59 H, th 27.12 H) 1.54-1.64 (-CH2 β from Ar,

aliphatic proton reference 4.00 H) 1.98-2.09 (CH2*=CH, exp 7.47 H, th 6.20 H) 2.49-2.57 (CH2—

Ar, exp 4.47 H, th 4.00 H) 2.76-2.87 (CH2*(=CH)2), exp 4.74 H, th 4.20 H) 2.99 (N-CH2*-CH2,

benzoxazine structure reference th 4.00 H) 4.03 (Ar-CH2-N, exp 3.98 H, th 4.00 H), 4.89 (O-CH2-N,

exp 4.00 H, th 4.00 H) 4.96-5.88 (CH=, exp 1.69, 7.55, 0.94 H, th 1.64, 6.48, 0.82 H) 6.60-6.90 (H-

Ar, exp 2.01, 2.07, 1.93 H th 2.00, 2.00, 2.00 H).

186

2.3.2 Synthesis of the di-vanillin Bz monomer

Vanillin (3.04 g, 20 mmol, 2 eq) was reacted with EDA (0.60 g, 10 mmol, 1 eq) and

paraformaldehyde (1.27 g, 40 mmol, 4 eq) in CHCl3 for 24 h. The product was purified over

column chromatography (Heptane/Ethyl acetate = 7/3) to yield a white powder.

1H NMR (CDCl3, 400 MHz, 298 K) δ = 3.02 (N-CH2*-CH2, exp 3.70 H, th 4.00 H) 3.95 (O-CH3,

benzoxazine structure reference 6.00 H) 4.13 (Ar-CH2-N, exp 4.01 H, th 4.00 H), 5.08 (O-CH2-N,

exp 4.02 H, th 4.00 H) 7.13-7.32 (H-Ar, exp 1.99, 1.99 H, th 2.00, 2.00 H) 9.81 ((C=O)H, exp 2.00

H, th 2.00 H).

2.3.3 Synthesis of the di-phenol Bz monomer

Phenol (1.88 g, 20 mmol, 2 eq) was reacted with EDA (0.60 g, 10 mmol, 1 eq), and

paraformaldehyde (1.27 g, 40 mmol, 4 eq) in CHCl3 at 70 °C for 24 h. The crude reaction was

washed three times with 1 M NaOH solution to remove unreacted phenolics and/or formed

oligomers, and the chloroform phase was neutralized by three washings with distilled water. The

crude reaction mixture was then washed with 1M NaOH solution and dried to obtain a white

powder.

1H NMR (CDCl3, 400 MHz, 298 K) δ = 3.02 (N-CH2*-CH2, exp 4.08 H, th 4.00 H) 4.07 (Ar-CH2-N, exp

4.02 H, th 4.00 H), 4.92 (O-CH2-N, exp 3.73 H, th 4.00 H) 7.78-7.15 (H-Ar, Ref 8.00 H, th 8.00 H)

9.81 ((C=O)H, exp 2.00 H, th 2.00 H).

2.3.4 Synthesis of the Vani-Card asymmetric Bz monomer

First reaction step: cardanol (5.98 g, 20 mmol, 1 eq) was reacted with EDA (1.20 g, 20 mmol, 1

eq) and paraformaldehyde (1.27 g, 40 mmol, 2 eq) in CHCl3 for 24 h. Second reaction step: vanillin

(3.04 g, 20 mmol, 1 eq) and paraformaldehyde (1.27 g, 40 mmol, 2 eq) were added to the reaction

crude and the reaction was continued for 24 h. The product was purified as described for di-

vanillin to yield a light orange wax.

1H NMR (CDCl3, 400 MHz, 298 K) δ = 0.85-0.96 (-CH3 from Cardanol alkyl chain, exp 2.04 H, th

1.77 H), 1.23-1.41 (-CH2 from cardanol alkyl chain, exp 13.53 H, th 13.56 H), 1.54-1.64 (-CH2 β

from Ar, aliphatic protons reference 2.00 H), 1.98-2.09 (CH2*=CH, exp 3.41 H, th 3.10 H), 2.49-

2,56 (CH2-Ar, exp 2.00 H, th 2.00 H), 2.75-2.87 (CH2*(=CH)2, exp 2.36 H, th 2.10 H), 2.95-3.09 (N-

CH2*-CH2, exp 3.99 H, th 4.00 H), 3.86-3.94 (O-CH3, benzoxazine structure reference 3.00 H), 4.01

(Ar-CH2-N from cardanol, exp 1.99 H, th 2.00 H), 4.13 (Ar-CH2-N from vanillin, exp 1.99 H, th 2.00

H), 4.88 (O-CH2-N from cardanol, exp 1.98 H, th 2.00 H), 4.96-5.88 (CH=, exp 1.00, 3.76, 0.46 H th

0.82, 3.24, 0.41 H) 5.08 (O-CH2-N from vanillin, exp 1.99 H, th 2.00 H), 6.60-6.88 (H-Ar from

187

cardanol, exp 1.07, 1.06, 1.00 H, th 1.00, 1.00, 1.00 H), 7.12-7.34 (H-Ar from vanillin, exp 1.00,

1.01 H, th 1.00, 1.00 H), 9.81 ((C=O)H, exp 1.01 H, th 1.00 H).

2.4 Material elaboration

Monomers (di-cardanol or Vani-Card) were degased during 1 h above melting temperature (50

and 105 °C, respectively) and then transferred to a U-shaped mold. A curing program of 1 h at

160 °C was applied followed by 2 h at 180 °C and the samples were post-cured for 2 h at 200 °C

and 30 min at 220 °C.

3 Chapter IV: Interpenetrating Polymers Networks (IPN) from cardanol-based thermoset

networks

3.1 Materials

CDGE (Commercial name NC-514) was supplied by Cardolite (EEW = 490 g/eq). 1,2-

diaminocyclohexane (mixture of isomers) was purchased from Sigma-Aldrich and used as

received. The EDBz benzoxazine monomer was synthetized and purified as described in the

Chapter III.


3.2.1 DSC analysis



from 20 to 250 °C at 20 °C/min rate for the analyses of the curing of the monomers.

The evolutions of the melting enthalpies of water were recorded on the swollen samples with the

following heating program at inert atmosphere (nitrogen): cooling from ambient temperature to

-50 °C at a rate of 20 °C/min, 5 min isotherm at -50 °C followed by a heating to 40 °C at a 5 °C/min

heating rate.

3.2.2 Solvent extraction

The solvents extractions of the materials at various curing steps were achieved by CHCl3

extractions in a Soxhlet for 72 h. After extraction the samples were dried under vacuum and then

weighed and characterized by DSC analysis.

188

3.2.3 DMA analysis

Dynamic mechanical analyses (DMA) were carried out on bar samples (5x10x0.5 mm3) with a

Q800 model (TA instruments) operating in tension mode with strain at 0.05 %; pretension, 10-2

N) at 1 Hz with a heating rate of 3 °C/min from ambient temperature to 250 °C.

3.3 Material elaboration

The reference materials from EDBz and CDGE, as well as the IPN materials with various

compositions, were elaborated by first mixing the CDGE pre-polymer and the EDBz compound at

100 °C and degasing during 1 h at 100 °C, followed by the addition of the IPD hardener in

stoichiometric ratio to the CDGE monomer (The stoichiometric amount of hardener was

determined by calculation with the equivalent epoxy weight EEW). The mixtures were then

transferred to a U-shaped mold. The previously determined curing program of 16 h at 100 °C, 1 h

at 160 °C, 2 h at 180 °C, 2 h at 200 °C and 30 min at 220 °C was applied to each material.

189

Annex: Figures

Figure 1. 1H NMR spectrum (in CDCl3) of cardanol.

Figure 2. Isothermal rheology monitoring of di-cardanol Bz monomer at 190 °C.

190

Figure 3. Isothermal rheology monitoring of Vani-Card Bz monomer at 190 °C.

191

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