copolyéthersulfones rigides-flexibles : modulation des propriétés … · 2018-04-25 · vi...
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Copolyéthersulfones rigides-flexibles : Modulation
des propriétés par modification du segment flexible
Thèse
Adrien Faye
Doctorat de chimie
Philosophiae doctor (Ph.D.)
Québec, Canada
© Adrien Faye, 2016
Copolyéthersulfones rigides-flexibles : Modulation
des propriétés par modification du segment flexible
Thèse
Adrien Faye
Sous la direction de :
Josée Brisson, directrice de recherche
iii
Résumé
La présente thèse traite trois thèmes principaux. Le premier volet concerne le contrôle
de la cristallinité et la synthèse des polyéthersulfones avec incorporation de doubles
liaisons comme espaceurs dans les chaînes du polymère en utilisant deux approches
différentes : la polymérisation par métathèse des diènes acycliques (ADMET) et la
polycondensation. L’ADMET a permis d’obtenir des copolymères de faibles
polydispersités avec des doubles liaisons régulièrement réparties le long des chaînes
du polymère. La polycondensation a permis d’obtenir des copolymères de
configuration cis ou trans avec incorporation régulière ou aléatoire des doubles
liaisons. Pour la synthèse par ADMET, un bloc rigide, terminé par des groupements
allyliques, est polymérisé dans le dichlorométhane à l’aide de l’un des catalyseurs de
Grubbs : Grubbs deuxième génération (G2) ou Hoveyda-Grubbs (HG). Concernant la
polycondensation, on fait réagir un bloc rigide avec un segment flexible de
configuration cis ou trans pour obtenir respectivement le copolymère cis ou trans. La
diffraction des rayons X et l’analyse enthalpique différentielle (DSC) ont montré que
l’isomère cis inhibe complètement la cristallinité alors que la forme trans la favorise.
Le deuxième volet de ce travail repose principalement sur la polycondensation en un
seul pot « one pot en anglais» qui a permis de contrôler les températures de transition
vitreuse. La spectrométrie de masse MALDI-TOF a permis de démontrer que les
copolymères obtenus avec variation du ratio bloc rigide/segment flexible sont de
nature aléatoire et non des copolymères blocs.
Le troisième et dernier thème de ce document concerne principalement le contrôle de
l’hydrophilicité par une post-fonctionnalisation des copolymères à travers les doubles
liaisons incorporées en utilisant les réactions thiol-ène clic. Le but étant de moduler
les propriétés des copolymères pour les adapter à des applications bien définies. Pour
une application dans la filtration membranaire par exemple, des chaînes hydrophiles
ont été greffées à travers ces doubles liaisons pour augmenter l’hydrophilicité des
copolymères.
iv
Abstract
This thesis deals with three main themes. The first component relates to the control of
the crystallinity and the synthesis of polyethersulfones with incorporation of double
bonds as a spacer in the polymer chains using two different approaches: ADMET
(Acyclic Diene Metathesis Polymerization) and polycondensation reactions. ADMET
leads to copolymers with low polydispersity index and double bonds regularly
distributed along the polymer chains. Polycondensation allows obtaining directly cis
or trans configuration copolymers with regular or random incorporation of the double
bonds. For the synthesis by ADMET, a rigid block terminated by allyl groups is
dissolved in dichloromethane and then polymerized using second generation Grubbs
catalyst (G2) and Hoveyda-Grubbs catalyst (HG). Concerning the polycondensation
reaction, a rigid block reacts with a flexible segment of cis or trans configuration to
respectively give the cis or trans copolymer. X-ray diffraction and differential
scanning calorimetry (DSC) showed that the cis isomer inhibits crystallization while
the trans form favors it.
The second part of this work is mainly based on the one-pot polycondensation
reaction which allowed control the glass transition. MALDI-TOF mass spectrometry
was used to show that copolymers obtained by the variation of the rigid bloc/flexible
segment ratio are random and not block copolymers.
The third subject of this document mainly concerns the control of the hydrophilicity
by post-functionalization of copolymers through the double bonds incorporated using
thiol-ene click reactions. The main goal is to modulate the properties of copolymers
to suit well-defined applications. For example, for applications in membrane
filtration, hydrophilic chains were grafted through double bonds to increase the
copolymer hydrophilicity.
v
Table des matières
Résumé ........................................................................................................................ iii Abstract ....................................................................................................................... iv
Table des matières ........................................................................................................ v Liste des tableaux ........................................................................................................ ix Liste des schémas ......................................................................................................... x Liste des figures .......................................................................................................... xi Abréviations .............................................................................................................. xiv
Symboles .................................................................................................................. xvii Dédicaces ................................................................................................................ xviii
Remerciements ........................................................................................................... xx
Avant-propos ............................................................................................................ xxii
Chapitre 1 : Introduction générale ............................................................................... 1 1.1 Revue de la littérature sur la synthèse des PES...................................................... 2
1.2 Les réactions thiol-ène clic radicalaires ................................................................. 5 1.3 Domaine d’application des PES ............................................................................. 7
1.3.1 Filtration membranaire ...................................................................................... 10 1.4 Problématique ...................................................................................................... 11 I.5 Objectif du projet .................................................................................................. 15
1.6 Méthodologie ....................................................................................................... 17 1.6.1 Polymérisation par métathèse des diènes acycliques (ADMET) ...................... 17
1.6.2 Polycondensation .............................................................................................. 21
1.6.3 Caractérisation des polymères ......................................................................... 22
1.6.4 Post-fonctionnalisation des copolymères ......................................................... 27 1.6.5 Mesures d’angle de contact ............................................................................... 27
1.7 Références ............................................................................................................ 30
Chapitre 2: Crystallization control of etherethersulfone copolymers by regular
insertion of an allyl functionality ............................................................................... 34 Résumé ....................................................................................................................... 35 Abstract ...................................................................................................................... 36
2.1 Introduction .......................................................................................................... 37 2.2 Experimental section ............................................................................................ 39 2.2.1 Instrumentation ................................................................................................. 39
2.2.2 Materials ............................................................................................................ 40 2.2.3 Synthesis of monomers ..................................................................................... 41 2.2.3.1 Synthesis of 4,4’-bis(4-methoxyphenoxy) diphenyl sulfone (MPDS)
(Scheme 2.1a) ............................................................................................................. 41
2.2.3.2 Synthesis of 4,4’-Bis(4-hydroxyphenoxy) diphenyl sulfone (HPDS) (Scheme
2.1a) ........................................................................................................................... 42 2.2.3.3 Synthesis of 4,4’-bis(4-allyloxyphenoxy) diphenyl sulfone (APDS) (Scheme
2.1a) ........................................................................................................................... 43
vi
2.2.3.4 Synthesis of 4-fluoro-4’-hydroxy diphenyl sulfone (FHDS) (Scheme 2.1b) . 44
2.2.3.5 Synthesis of 4-fluoro-4’-methoxy diphenyl sulfone (FMDS) (Scheme 2.1b) 44
2.2.3.6 Synthesis of 4,4’-bis(4-(4-(4-methoxyphenylsulfonyl)
phenoxy)pentoxy)diphenylsulfone (MPSPPDS) (Scheme 2.1b)................................ 45 2.2.3.7 Synthesis of 4,4’-bis(4-(4-(4-hydroxyphenylsulfonyl)phenoxy)phenoxy)
diphenyl sulfone (HPSPPDS) (Scheme 2.1b)............................................................. 46 2.2.4 Copolymer synthesis ......................................................................................... 46
2.2.4.1 ADMET polymerization of poly(allyl-co-etherethersulfone) (PA-4EES)
(Scheme 2.2a) ............................................................................................................. 46 2.2.4.2 Polycondensation of PTA-4EES, PTCA-4EES, PTA-8EES and PCA-8EES
copolymers (Schemes 2.2b and 2.2c) ......................................................................... 47 2.2.4.3 Polycondensation of the PAE-4EES copolymer (Scheme 2.2d) .................... 47
2.2.4.4 Hydrogenation to obtain PAH-4EES and PAH-8EES ................................... 47
2.2.4.5 Halogenation to obtain PACl-4EES and PABr-4EES ................................... 48 2.2.5 Recrystallization of copolymers. ....................................................................... 48
2.2.6 Results and discussion ...................................................................................... 49
2.2.6.1 Synthesis of polymers .................................................................................... 49 2.2.6.1.1 PA-4EES copolymer obtained by ADMET polymerization ....................... 50
2.2.6.1.2 PTA-xEES and PCA-xEES polymers obtained by polycondensation ........ 52 2.2.7 Post-polymerization reactions ........................................................................... 55 2.2.8 Thermal properties of the copolymers .............................................................. 57
2.2.8.1 Thermogravimetric analysis (TGA) ............................................................... 57 2.2.8.2 Differential scanning calorimetry (DSC) ....................................................... 58
2.2.9 X-ray diffraction................................................................................................ 62 2.2.10 Double melting behaviour ............................................................................... 68
2.3 Conclusion ........................................................................................................... 70 2.4 Acknowledgements .............................................................................................. 71
2.5 References ............................................................................................................ 72
Chapitre 3: Synthesis of High Molecular Weight Polyetherethersulfone - Allyl
Copolymers of Controlled glass transition ................................................................ 74 Résumé ....................................................................................................................... 75
Abstract ...................................................................................................................... 76 3.1 Introduction .......................................................................................................... 77 3.2 Experimental section ............................................................................................ 78 3.2.1 Instrumentation ................................................................................................. 78 3.2.2 Materials ............................................................................................................ 80
3.2.3 Synthesis of the monomer: 4,4’-bis(4-hydroxyphenoxy) diphenyl sulfone
(HPDS) ....................................................................................................................... 80
3.2.4 Polymers synthesis ............................................................................................ 80 3.2.4.1 PEES synthesis10 ............................................................................................ 80 3.2.4.2 Synthesis of poly(4EES-alt-cb) and poly(4EES-alt-tb) ................................. 81 3.2.4.3 Synthesis of poly(6EES-ran-4EEScb) ........................................................... 83 3.2.5 Copolymer film preparation .............................................................................. 83
3.2.6 Chemical aging studies ..................................................................................... 83
vii
3.3 Results and discussion ......................................................................................... 84
3.3.1 Optimization of the synthesis of poly(4EES-alt-cb) and poly(4EES-alt-tb) ..... 84
3.3.2 One-pot synthesis of copolymers with longer rigid segments, poly(6EES-ran-
4EEScb)...................................................................................................................... 86 3.3.3 MALDI-TOF investigation of the copolymers ................................................. 88 3.3.4 Thermal properties of copolymers .................................................................. 100 3.3.4.1 Thermogravimetric analyses ........................................................................ 100
3.3.4.2 DSC measurements ...................................................................................... 101 3.3.5 Chemical aging studies ................................................................................... 104 3.4 Conclusion ......................................................................................................... 107 3.5 Acknowledgements ............................................................................................ 107 3.6 References .......................................................................................................... 108
Chapitre 4: Postfunctionalization by thiol-ene click reactions of
polyetherethersulfone-allyl copolymers for applications in membrane filtration ... 109
Résumé ..................................................................................................................... 110
Abstract .................................................................................................................... 111 4.1 Introduction ........................................................................................................ 112
4.2 Experimental section .......................................................................................... 114 4.2.1 Instrumentation ............................................................................................... 114 4.2.2 Materials .......................................................................................................... 115
4.2.3 Synthesis of S-2-(2-(2-hydroxyethoxy)ethoxy)ethyl thioacetate (scheme
4.1)20 ......................................................................................................................... 116
4.2.4 Synthesis of 2-(2-(2-hydroxyethoxy)ethoxy)ethanethiol (PEG2-thiol) (scheme
4.1)21 ......................................................................................................................... 116
4.2.5 Synthesis of the monomer: 4,4’-bis(4-hydroxyphenoxy) diphenyl sulfone
(HPDS) ..................................................................................................................... 117
4.2.6 Polymers and copolymers used in this work ................................................... 117 4.2.7 Post-functionalization of copolymers by thiol-ene click reactions19 .............. 118 4.2.8 Solubility test of the cross-linked copolymer ................................................. 122
4.2.9 CHNS Elementary Analysis ............................................................................ 122 4.2.9.1 Cross-linking with 2,2′-(ethylenedioxy) diethanethiol (PEG2-dithiol) ........ 123
4.2.9.1.1 Theoretical percentage calculation of carbon atoms contained in the
copolymer after cross-linking (poly(4EES-alt-cb)-crosslink-PEG2), considering one
chain grafted per double bond .................................................................................. 123 4.2.9.1.2 Theoretical percentage calculation of carbon atoms contained in the
copolymer after cross-linking (poly(4EES-alt-cb)-crosslink-PEG2) considering two
chains grafted per double bond ................................................................................ 124 4.2.9.2 Cross-linking with 1,3-propanedithiol (Pr-dithiol) ...................................... 124
4.2.9.2.1 Theoretical percentage calculation of carbon atoms contained in the
copolymer after cross-linking (poly(4EES-alt-cb)-crosslink-Pr) ............................. 124 4.2.10 Cross-link density measurements .................................................................. 125 4.2.11 Copolymer film preparation .......................................................................... 127 4.2.12 Cross-linked copolymer film preparation ..................................................... 127
4.3 Results and discussion ....................................................................................... 127
viii
4.3.1 PES and PEES ................................................................................................. 127
4.3.2 Alternate and random copolymer synthesis .................................................... 128
4.3.3 Post-functionalization of copolymers by thiol-ene click reactions ................. 128 4.3.4 Hydrophilicity and hydrophobicity studies ..................................................... 135 4.3.5 Film cross-linking ........................................................................................... 137 4.4 Conclusion ......................................................................................................... 140 4.5 Acknowledgements ............................................................................................ 141
4.6 References .......................................................................................................... 142
Chapitre 5 : Conclusion et Recommandations ......................................................... 144 5.1 Références .......................................................................................................... 149 Annexes .................................................................................................................... 150
Bibliographie générale ............................................................................................. 176
ix
Liste des tableaux
Tableau 1.1 : Famille des polyéthersulfones avec leurs abréviations, structures
chimiques, noms commerciaux, producteurs et années de synthèse1 .......................... 2
Tableau 1.2: Réactivité des catalyseurs à base de titane, tungstène, molybdène et
ruthénium vis-à-vis des oléfines en présence de groupements fonctionnels
hétéroatomiques62 ....................................................................................................... 18
Table 2.1: Molecular weights and dispersity of polymers synthesized by ADMET
and polycondensationa ............................................................................................... 56
Table 2.2: Proton chemical shifts (d) of the allyl group in cis- and trans
poly(etherethersulfones) obtained by polycondensation and by ADMET (major
configuration trans) .................................................................................................... 57
Table 3.1: Monomer ratios used in the synthesis of poly(6EES-ran-4EEScb) ......... 83
Table 3.2: Number molecular weight (Mn), degree of polymerization (DP) and
polydispersity index (Ip) of Poly(4EES-alt-tb), Poly(4EES-alt-cb) and PEES ......... 85
Table 3.3: DSC and SEC data of copolymers synthesized with varying
6EES/4EEScb ratios ................................................................................................... 87
Table 3.4: Proposed assignment for the main MALDI-TOF fragments of the PEES
homopolymer ............................................................................................................. 91
Table 3.5: Proposed assignment for the main MALDI-TOF fragments for the
poly(4EES-alt-cb) in the 1000 - 5000 g mol−1 range (only the most intense peaks are
reported in this Table) ................................................................................................ 92
Table 3.6: Proposed assignment for the main MALDI-TOF fragments for the
poly(6EES-ran-4EEScb) in the 1000 - 3500 g.mol−1 range (only the most intense
peaks are reported in this Table) ................................................................................ 93
Table 3.7: Proposed assignment for additional MALDI-TOF fragments for the
poly(4EES-alt-cb) and poly(6EES-ran-4EEScb) in the 1000 - 4000 g mol−1 range .. 97
Table 3.8: Number molecular weight (Mn) and polydispersity index (Ip) of
poly(4EES-alt-cb) and poly(6EES-ran-4EEScb) copolymers before and after
immersed in bleach .................................................................................................. 105
Table 4.1: Grafted and cross-linked molecules and their abbreviations ................. 119
Table 4.2: Number molecular weights (Mn), degree of polymerization (DP) and
polydispersity index (Ip) of synthesized polyethersulfone (PES) and
polyetherethersulfone (PEES) .................................................................................. 127
Table 4.3: Number molecular weight, polydispersity index, glass transition
temperature and contact angles of copolymers and functionalized copolymers ...... 129
Table 4.4: Carbon elementary analysis and solubility of copolymers cross-linked
with PEG2-dithiol and Pr-dithiol. ............................................................................ 135
Table 4.5: Glass transition temperatures and contact angles of Poly(6EES-ran-
4EEScb) before and after surface cross-linking ....................................................... 138
Table A.2.1: Comparison of diffraction peak position for PES and polymers
synthesized in the present work ............................................................................... 150
x
Liste des schémas
Schéma 1.1 : Formule chimique du PES ..................................................................... 1 Schéma 1.2 : Synthèse des PES par polysulfonylation utilisée par 3M Corporation12 3
Schéma 1.3 : Synthèse des PES par polyétherification utilisée par Union Carbide
Corporation et ICI12...................................................................................................... 4 Schéma 1.4 : Synthèse des PEES par polyétherification utilisée par Plastics division
of ICI12 ......................................................................................................................... 4 Schéma 1.5 : Mécanisme de substitution nucléophile aromatique .............................. 5
Schéma 1.6 : Mécanisme radicalaire du DMPA26 ....................................................... 7 Schéma 1.7 : Mécanisme de la réaction thiol-ène clic18,25,27 ....................................... 7
Schéma 1.8 : Catalyseurs de Grubbs utilisés pour l’ADMET................................... 19
Schéma 1.9: Polymérisation par métathèse des diènes acycliques (ADMET) .......... 20 Schéma 1.10 : Mécanisme de polymérisation par métathèse des diènes acycliques
(ADMET)69,70 ............................................................................................................. 21 Schéma 1.11: Illustration de la polycondensation entre un bloc rigide et un segment
flexible........................................................................................................................ 22 Schéma 1.12: Principe de fonctionnement d’un spectromètre de masse MALDI-
TOF.72 ........................................................................................................................ 25 Scheme 2.1: Synthesis of monomer precursors: (a) APDS (4-ring) precursor and (b)
HPSPPDS (8-ring) precursor ..................................................................................... 42
Scheme 2.2: Polymerization reactions: (a) acyclic diene metathesis polymerization
(ADMET) of the APDS monomer, (b) polycondensation of HPDS with (Z) and (E)-
1,4-dichlorobut-2-ene, (c) polycondensation of HPSPPDS with (Z) and (E)-1,4-
dichlorobut-2-ene and (d) polycondensation with fumaryl chloride to insert ester
linkages. ..................................................................................................................... 49 Scheme 3.1: Synthesis of random and alternate copolymers: a) Poly(4EES-alt-cb)
and poly(4EES-alt-tb) alternate copolymers and b) Poly(6EES-ran-4EEScb) random
copolymer (one pot polycondensation reaction) ........................................................ 82 Scheme 3.2: Repeat units and molar masses of various copolymers reported in the
MALDI-TOF study .................................................................................................... 94 Scheme 4.1: Synthesis of 2-(2-(2-hydroxyethoxy)ethoxy)ethanethiol (PEG2-thiol)116 Scheme 4.2 : Polymers and copolymers used in this work...................................... 117
Scheme 4.3: Thiol-ene click reactions onto poly(4EES-alt-cb) copolymer : a) PEG2-
thiol chain grafting and b) Pr-dithiol and PEG2-dithiol chains cross-linking .......... 120 Schéma 5.1 : Illustration de la possibilité d’une liaison intramoléculaire entre
l’oxygène proche de la double liaison et le métal central du catalyseur2................. 145 Schéma A.2.1: Mn calculation by NMR .................................................................. 167
xi
Liste des figures
Figure 1.1 : Filtration du lait caillé pour la production du fromage ............................... 9
Figure 1.2 : Principe d’une membrane de filtration selon Prulho41 ............................. 10
Figure 1.3 : Images MEB en coupe plane (a) et transversale (b) d’une membrane
colmatée (agrégat de particules encerclé en vert) 50 ...................................................... 14
Figure 1.4 : Images MEB d’une coupe transversale d’une membrane de PES seul (a)
et d’un mélange PES/PAN dans un rapport massique 70/30 (d), telles que publiées par
Amirilargani et al.57 ...................................................................................................... 15
Figure 1.5 : Comparaison des masses molaires obtenues par ADMET avec les
catalyseurs de Grubbs deuxième génération et Hoveyda – Grubbs dans différents
solvants63 ....................................................................................................................... 19
Figure 1.6: Composants basiques d’un spectromètre MALDI-TOF utilisable en mode
linéaire et mode réflectron72 .......................................................................................... 26
Figure 1.7: Mesure de l’angle de contact ..................................................................... 28
Figure 1.8: Principe de mesure de l’angle de contact .................................................. 29
Figure 2.1: 1H-NMR spectrum of the representative monomer and polymers obtained
by ADMET: (a) PA-4EES, Mn = 2200 g mol-1 and (b) enlargement showing end-
groups for PA-4EES with two different molecular weights and for the monomer. ...... 54
Figure 2.2: Thermal stability of representative 4-ring and 8-ring polymers as
determined by thermogravimetry. ................................................................................. 58
Figure 2.3: Differential scanning calorimetry: (a) heating and cooling scans for PA-
4EES and (b) first heating scan for representative polymers ........................................ 59
Figure 2.4: X-ray diffraction diagrams of PA-4EES as recrystallized by evaporation
from various solvents .................................................................................................... 63
Figure 2.6: Molecular models of chain folding due to allyl groups: (a) chain fold
models and (b) extended chain conformation, showing deviation from linearity......... 68
Figure 2.7: Investigation of the double melting behaviour of PA-4EES ..................... 69
a) Representative DSC scans of PA-4EES and b) X-ray diffraction diagrams as
synthesized and after Annealing between Tm1 and Tm2 and rapid quenching ............... 69
Figure 3.1: 1H-NMR spectra of poly(6EES-ran-4EEScb) random copolymers........... 88
Figure 3.2: Representative MALDI-TOF mass spectrum of synthesized copolymers
a) PEES homopolymer b) Poly(4EES-alt-cb) and c) Poly(6EES-ran-4EEScb), ratio
70/30 .............................................................................................................................. 90
Figure 3.3: Thermogravimetric degradation curves of poly(4EES-alt-cb) (0/100),
PEES homopolymer (100/0) and random copolymers with varying 6EES/4EEScb
ratios ............................................................................................................................ 100
Figure 3.4: DSC curves of poly(4EES-alt-cb) (0/100), PEES homopolymer (100/0)
and random copolymers with varying 6EES/4EEScb ratios ....................................... 103
Figure 3.5: Changes in glass transition temperatures with varying 6EES weight % in
poly(6EES-ran-4EEScb) copolymers ......................................................................... 104
Figure 3.6: FTIR spectra of poly(6EES-ran-4EEScb) copolymer before and after
immersion in bleach: a) from 500 to 1900 cm-1 and b) from 2600 ............................ 106
xii
Figure 4.1: FTIR spectra of poly(4EES-alt-cb) and poly(4EES-alt-cb)-graft-PEG2: a)
from 700 to 1900 cm-1 and b) from 2500 to 4000 cm-1 .............................................. 130
Figure 4.2: 1H-NMR spectra of Poly(4EES-alt-cb) and Poly(4EES-alt-cb)-graft-
PEG2 ............................................................................................................................ 131
Figure 4.3: FTIR spectra of Poly(6EES-ran-4EEScb) and Poly(6EES-ran-4EEScb)-
graft-PEG16 a) from 700 to 1900 cm-1 and b) from 2500 to 4000 cm-1 .................... 133
Figure 4.4: 1H-NMR spectra of Poly(6EES-ran-4EEScb) and Poly(6EES-ran-
4EEScb)-graft-PEG16 .................................................................................................. 133
Figure 4.5: Contact angles of PES, PEES, alternate copolymer (Poly(4EES-alt-cb)),
and alternate copolymer after cross-linking or grafting .............................................. 136
Figure 4.6: Contact angles of the random copolymer (Poly(6EES-ran-4EEScb)) before
and after grafting or cross-linking ............................................................................... 137
Figure 4.7: FTIR spectra of Poly(6EES-ran-4EEScb) before and after surface-cross-
linking ......................................................................................................................... 139
Figure A.2.1: NMR spectra of 4,4’-bis(4-methoxyphenoxy) diphenyl sulfone (MPDS)
in CDCl3 ..................................................................................................................... 153
Figure A.2.2: NMR spectra of 4,4’-bis(4-hydroxyphenoxy) diphenyl sulfone (HPDS)
in DMSO ..................................................................................................................... 154
Figure A.2.3: NMR spectra of 4,4’-bis(4-allyloxyphenoxy) diphenyl sulfone (APDS)
in CDCl3 ...................................................................................................................... 155
Figure A.2.4: 1H-NMR spectrum of a) (Z)-1,4-dichlorobut-2-ene in CDCl3 and b) (E)-
1,4-dichlorobut-2-ene in CDCl3 .................................................................................. 156
Figure A.2.5: NMR spectra of 4-fluoro-4’-hydroxy diphenyl sulfone (FHDS)........ 157
Figure A.2.6: NMR spectra of 4-fluoro-4’-methoxy diphenyl sulfone (FMDS) ...... 158
Figure A.2.7: NMR spectra of 4,4'-bis(4-(4-(4-
methoxyphenylsulfonyl)phenoxy)phenoxy) diphenyl sulfone (MPSPPDS) in
CDCl3 .......................................................................................................................... 159
Figure A.2.8: NMR spectra of 4,4'-bis(4-(4-(4-
hydroxyphenylsulfonyl)phenoxy)phenoxy) diphenyl sulfone (HPSPPDS) in
DMSO ......................................................................................................................... 160
Figure A.2.9: 1H-NMR spectrum of poly(allyl-co-ether ether sulfone ether) (PA-
4EES) in CDCl3 .......................................................................................................... 161
Figure A.2.10: 1H-NMR of the 4-ring polymers obtained by polycondensation ....... 165
Figure A.2.11: Comparison of PTA-4EES NMR spectra before and after heating,
showing the persistence of the trans signals ............................................................... 166
Figure A.3.1: Representative MALDI-TOF mass spectrum of Poly(6EES-ran-
4EEScb), ratio 50/50 ................................................................................................... 168
Figure A.3.2: Representative MALDI-TOF mass spectrum of Poly(6EES-ran-
4EEScb), ratio 60/40 ................................................................................................... 168
Figure A.3.3: Representative MALDI-TOF mass spectrum of Poly(6EES-ran-
4EEScb), ratio 80/20 ................................................................................................... 169
Figure A.3.4: Representative MALDI-TOF mass spectrum of Poly(6EES-ran-
4EEScb), ratio 90/10 ................................................................................................... 169
Figure A.4.1: NMR spectra of S-2-(2-(2-hydroxyethoxy)ethoxy)ethyl thioacetate in
CDCl3 ......................................................................................................................... 170
xiii
Figure A.4.2: NMR spectra of 2-(2-(2-hydroxyethoxy)ethoxy)ethanethiol in
CDCl3 .......................................................................................................................... 171
Figure A.4.3: FTIR spectra of Poly(6EES-ran-4EEScb) and Poly(6EES-ran-4EEScb)-
graft-C8 a) from 700 to 1900 cm-1 and b) from 2500 to 4000 cm-1 ........................... 172
Figure A.4.4: 1H-NMR spectra of Poly(6EES-ran-4EEScb) and Poly(6EES-ran-
4EEScb)-graft-C8 ........................................................................................................ 173
Figure A.4.5: FTIR spectra of Poly(4EES-alt-cb) and Poly(4EES-alt-cb)-crosslink-
Pr ................................................................................................................................. 174
a) from 700 to 1900 cm-1 and b) from 2500 to 4000 cm-1 .......................................... 174
Figure A.4.6: FTIR spectra of Poly(4EES-alt-cb) and Poly(4EES-alt-cb)-crosslink-
PEG2 a) from 700 to 1900 cm-1 and b) from 2500 to 4000 cm-1 ................................. 175
xiv
Abréviations
Å : Ångström
ADMET : Polymérisation par métathèse des diènes acycliques (acyclic
diene metathesis polymerization)
alt : Alternate
APDS : 4,4’-Bis(4-allyloxyphenoxy) diphenyl sulfone
BBr3 : Tribromure de bore
cb : cis but-2-ène
CDCl3 : Chloroforme deutérié
CHCl3 : Chloroforme
CH2Cl2 : Dichlorométhane
CH3I : Iodure de méthane
Cl : Chlore
C8 : Octane
d : Doublet
dd : Doublet de doublet
DMAc : N,N-Diméthylacétamide
DMF : N,N-Dimethyformamide
DMPA : 2,2-diméthoxy-2-phénylacetophénone
DMSO : Diméthylsulfoxyde
DMSO-d6 : Diméthylsulfoxyde deutérié
DP : Degré de polymérisation
DSC : Calorimétrie différentielle à balayage ou analyse
enthalpique différentielle
E-DCB : (E)-1,4-dichlorobut-2-ène
EES : Éther éther sulfone
EESE : Éther éther sulfone éther
EG : End-group
FHDS : 4-Fluoro-4’-hydroxy diphenyl sulfone
FMDS : 4-Fluoro-4’-methoxy diphenyl sulfone
FTIR : Spectroscopie infrarouge à transformée de Fourier
FTIR-ATR : Spectroscopie infrarouge par réflexion totale atténuée
G2 : Catalyseur de Grubbs de deuxième génération (Grubbs
second generation catalyst)
H : Hydrogène ou proton
HCl : Acide chlorhydrique
HG : Hoveyda–Grubbs catalyst
HPDS : 4,4’-Bis(4-hydroxyphenoxy) diphenyl sulfone
HPSPPDS : 4,4’-Bis(4-(4-(4-hydroxyphenylsulfonyl)phenoxy)phenoxy)
diphenyl sulfone
I : Intensité
Ip : Indice de polydispersité
IR : Infrarouge
xv
K2CO3 : Carbonate de potassium
KOH : Solution aqueuse d’hydroxyde de potassium
kV : kilovolt
Li : Lithium
m : Multiplet
M : Molaire
mA : milliampère
MALDI-TOF : Matrix-Assisted Laser Desorption Ionization –Time Of
Flight
MEB : Microscopie Électronique à Balayage
mg/mL : Milligramme par millilitre
MgSO4 : Sulfate de magnésium
MHz : Méga Hertz
mL : Millilitre
mmol : Millimole
Mn : Masse molaire moyenne en nombre
MPa : Mégapascal
MPDS : 4,4’-Bis(4-methoxyphenoxy) diphenyl sulfone
MPSPPDS : 4,4’-Bis(4-(4-(4-methoxyphenylsulfonyl) phenoxy)pentoxy)
diphenyl sulfone
Mw : Masse molaire moyenne en poids
m/z : Ratio masse sur charge
NaCl : Chlorure de sodium
NaI : Iodure de sodium
NaOH : Hydroxyde de sodium
NaHCO3 : Bicarbonate de sodium
nm : Nanomètre
NMP : N-Méthyl-2-pyrrolidone
PA-4EES : Poly(allyl-co-ether ether sulfone ether )
PABr-4EES : Poly(brominated allyl-co-ether ether sulfone ether)
PACl-4EES : Poly(chlorinated allyl-co-ether ether sulfone ether)
PAE-4EES : Poly(trans-allyl-co-ether ether sulfone ester)
PAH-4EES : Poly(hydrogenated allyl-co-ether ether sulfone ether)
PAN : Polyacrylonitrile
PCA-4EES : Poly(cis-allyl-co-ether ether sulfone ether)
PEG : Polyéthylène glycol
PEEK : polyétheréthercétone
PEES : Polyétheréthersulfone
PES : Polyéthersulfone
PPTA : Poly(para-phénylène térephthalamide)
ppm : Partie par million
Pr-dithiol : Propanedithiol
PTA-4EES : Poly(trans-allyl-co-ether ether sulfone ether)
ran : Random
RMN : Résonance magnétique nucléaire
xvi
RMN 13C : Résonance magnétique nucléaire du carbone 13
RMN 1H : Résonance magnétique nucléaire du proton
s : Singulet
SEC : Chromatographie d’exclusion stérique
SEM : Scanning Electron Microscopy
t : Triplet
tb : trans but-2-ène
Tg : Température de transition vitreuse
TGA : Analyse thermogravimétrique
Tm : Température de fusion
TMS : Tetraméthysilylane
UV : Ultraviolet
WAXS : «Wide Angle X-ray Scattering» ou diffraction des rayons X
aux grands angles
Z-DCB : (Z)-1,4-dichlorobut-2-ène
xvii
Symboles
𝑑𝑠 : Densité du solvant g/cm3
𝑑𝑝 : Densité du copolymère en g/cm3
𝑀𝑐 : Masse molaire moyenne en nombre entre les ponts de réticulation
𝑀𝑠 : Masse molaire du solvant g/mol 𝑚𝑝 : Masse du copolymère avant gonflement
𝑚𝑡 : Masse du copolymère à l’équilibre après gonflement (copolymère +
solvant)
𝑅 : Constante des gaz parfaits
𝑇 : Température absolue
𝑉𝑠 : Volume molaire du solvant en cm3/mol
𝑉𝑝 : Fraction volumique du copolymère à l’équilibre après absorption
du solvant
𝑉𝑝𝑟 : Fraction volumique du copolymère réticulé
𝛽 : Constante de réseau
𝛿 : Paramètre de solubilité
𝜒 : Paramètre d’interaction solvant/copolymère
𝜒𝐷𝑆𝐶 : Taux de cristallinité obtenu par DSC
𝜒𝑋−𝑟𝑎𝑦 : Taux de cristallinité obtenu par diffraction des rayons X
𝜌 : Densité du copolymère g/cm3
θ : Thêta
% : Pourcentage
° : Degré
°C : Degré Celsius
°C/min : Degré Celsius par minute
𝛥𝐻 : Enthalpie de fusion
xviii
Dédicaces
Je dédie ce mémoire à :
Ma mère, qui a œuvré pour ma réussite, de par son amour, son soutien, tous les
sacrifices consentis et ses précieux conseils, pour toute son assistance et sa présence
dans ma vie, reçois à travers ce travail aussi modeste soit-il, l'expression de mes
sentiments et de mon éternelle gratitude.
Mon père, qui peut être fier et trouver ici le résultat de longues années de sacrifices et
de privations pour m'aider à avancer dans la vie. Puisse Dieu faire en sorte que ce
travail porte son fruit ; Merci pour les valeurs nobles, l'éducation et le soutien
permanent venu de toi.
Mes frères et sœurs (Jacqueline, Diory, Rose, Sobel, Mane, Mbalam, Watéo, Mame
Coumba, Mame Latsouck et Marie Ngounda et à mes demi-frères et demi-sœurs
(Diouly, Gnilane et Sara) qui n'ont cessé de m’encourager et d'être pour moi des
exemples de persévérance et de courage.
La femme de ma vie, Salimata Ndiaye, mon âme sœur, la lumière de mon chemin.
Ma vie à tes cotés est remplie de belles surprises. Tes sacrifices, ton soutien moral et
matériel, tes encouragements sans cesse, ta gentillesse sans égal, ton profond
attachement m'ont permis d’arriver au bout de ce travail.
xix
« Telle est bien la beauté et la
noblesse de la science : désir sans
fin de repousser les frontières du
savoir, de traquer les secrets de la
matière et de la vie sans idée
préconçue des conséquences
éventuelles. »
Marie Curie
xx
Remerciements
Je souhaite adresser mes remerciements les plus sincères à toutes les personnes qui
ont contribué de prêt ou de loin à la réussite de cette thèse.
Nulle œuvre n'est exaltante que celle réalisée avec un soutien moral et financier.
D’abord, je remercie ma Directrice de thèse, la Professeure Josée Brisson, de m’avoir
donné l’opportunité d’intégrer son groupe de recherche, de m’avoir soutenu et permis
d’explorer le domaine fascinant de la synthèse des polymères et de leurs
caractérisations. Vous ne cessiez pas de m’encourager, encore m’encourager, toujours
m’encourager à aller jusqu’au bout de mes synthèses pour l’obtention de copolymères
de hautes masses molaires. Vos nombreux conseils, votre imagination et votre
énergie tout au long de ce travail ont été, pour moi, une véritable source de
motivation afin de mener à bien ce projet. J'aimerais également lui dire à quel point
j’ai apprécié sa grande disponibilité tout au long de cette thèse plus particulièrement
durant les moments de correction des articles et de ce document. Enfin, j’ai été
extrêmement sensible à ses qualités humaines, d'écoute et de compréhension tout au
long de ce travail doctoral.
Je souhaite continuer à la côtoyer dans le futur aussi bien dans le cadre professionnel
que personnel.
J’adresse également mes remerciements au Professeur Jean-François Morin pour ses
conseils et pour m’avoir permis d’opérer les réactions thiol-ène clic dans son
laboratoire, mais aussi, pour avoir accepté de faire partie des membres du jury.
Mes remerciements vont également à la Professeure Maria-Cornelia Iliuta pour avoir
mis, à ma disposition, les équipements de son laboratoire et de m’aider à procéder
aux mesures d’angles de contact.
Je sais infiniment gré au Professeur Jérôme Claverie de l’UQAM de s’être rendu
disponible et d’avoir accepté la fonction d’examinateur externe pour cette thèse.
xxi
Je suis particulièrement reconnaissant au Professeur Peter McBreen de l’intérêt qu’il
a porté à l’égard de ce travail en acceptant de faire partie du jury.
Mes remerciements vont également à Madame Plesu (TGA, DSC, SEC, Rayons X),
Monsieur Audet (RMN), Monsieur Groleau (CHNS), Monsieur Paquet-Mercier
(FTIR) et Madame Furtos de l’Université de Montréal (MALDI-TOF).
Je tiens à remercier vivement tous les membres du groupe de la Professeure Brisson :
Huan Liang, Abdelkader Benhalima, Simon Provencher, François Hudon et Marianne
P. Ouattara. Mention spéciale à Huan Liang, avec qui, j’ai mené des discussions
enrichissantes en ce qui concerne nos projets. Je voudrais remercier particulièrement
les étudiants stagiaires : Mikaël Leduc qui a participé à l’optimisation du choix du
solvant utilisé pour la recristallisation des copolymères présentés dans le chapitre 2 et
Jacob Dion Gagné, pour son aide à la préparation des films de polymère.
Enfin, ces remerciements ne peuvent s’achever sans une pensée particulière pour tous
mes proches et amis qui m’ont toujours soutenu et encouragé dans les bons comme
dans les moments plus difficiles. Merci à toutes et tous !
xxii
Avant-propos
Cette thèse a été rédigée sous la direction de Madame Josée Brisson, Professeure
titulaire au département de chimie de l’Université Laval. En étroite collaboration avec
ma directrice de recherche, j’ai joué un rôle de premier plan dans la synthèse et la
caractérisation des copolymères ainsi que dans la rédaction des articles et de ce
document.
Cette thèse comprend cinq chapitres. Le premier et le cinquième chapitre décrivent
respectivement l’introduction générale et la conclusion générale. Les chapitres 2, 3, et
4 ont chacun fait l’objet d’un document sous forme d’article qui a été publié ou sera
soumis pour publication dans une revue scientifique. Pour chacun de ces articles, j’ai
œuvré comme auteur principal en procédant aux synthèses et à la majeure partie des
caractérisations des copolymères, en rédigeant la première version des articles, en
apportant les modifications suggérées par la professeure Brisson pour tous les
articles, mais également, celles suggérées par les arbitres de l’article dans le cas du
Chapitre 2.
Les co-auteurs de ces manuscrits ont largement contribué à leur réalisation en
participant à l’optimisation de certaines méthodes de caractérisation ou en procédant
à leur révision, en plus des conseils et des orientations. Tous mes remerciements à :
Mikaël Leduc (Chapitre 2), qui a participé à l’optimisation du choix du solvant
utilisé pour la recristallisation des copolymères.
Alexandra Furtos (Chapitre 3), qui nous a aidé dans l’enregistrement des spectres
MALDI-TOF et a confirmé notre interprétation
Jean-François Morin (Chapitre 4), qui a proposé certaines voies ou conditions de
synthèse, notamment pour les synthèses thiol-ène clic.
Maria Cornelia Iliuta (Chapitre 4), qui nous a assisté dans l’enregistrement des
mesures d’angles de contact et dans leur interprétation.
xxiii
Hormis les articles scientifiques, ce travail a fait l’objet de plusieurs présentations
dans des conférences nationales et internationales qui sont les suivantes:
A. Faye, J. Brisson, Synthesis and postfunctionalization of polyetherethersulfone-
allyl copolymers for applications in membrane filtration, Sustainable Materials
Science and Technology, Paris, France, juillet 2015.
A. Faye, J. Brisson, Synthesis and crystallization control of polyetherethersulfone
copolymers by regular insertion of an allyl functionality, High Polymer Forum,
Gananoque, Canada, juillet 2014.
A. Faye, J. Brisson, Synthesis Route for Crystalline Polyethersulfone Copolymers,
96th Canadian Chemistry Conference and Exhibition, Quebec, Canada, mai 2013.
A. Faye, J. Brisson, Synthesis of Polyethersulfone Copolymers via ADMET, High
Polymer Forum, Gananoque, Canada, août 2012.
1
Chapitre 1 : Introduction générale
Les polyéthersulfones (PES) sont des polymères amorphes de la famille des
poly(arylène éther sulfone)s et dont la structure chimique est composée de noyaux
aromatiques liés à des groupements sulfonyles (-SO2-) et éthers (-O-) (Schéma 1.1).
Les groupements phényles et sulfones sont responsables de la résistance à la chaleur
et à l'oxydation, tandis que les éthers contribuent beaucoup à la flexibilité de la
chaîne.
Schéma 1.1 : Formule chimique du PES
L’unité de répétition, bien qu’étant régulière, ne permet pas d’obtenir facilement des
arrangements ordonnés en raison de l’alternance des groupements éther et sulfone,
chacun ayant un angle de valence différent, ce qui nuit à un empilement de chaîne
régulier.1,2 La forte polarité des liaisons sulfones conduit à un effet d’attraction
d'électrons qui délocalise les électrons π des noyaux aromatiques, ce qui a tendance à
donner un caractère de double liaison aux liaisons C-S de la chaîne. Une telle
délocalisation augmente considérablement la barrière de rotation autour des liaisons
C-S et par conséquent la rigidité de la chaîne, 3 gênant ainsi leur repliement. Cette
rigidité intrinsèque de la chaîne a également pour conséquence de rendre élevées les
températures de transition vitreuse (Tg) de ces matériaux (230 °C environ).4
D’autre part, l'angle de valence C-S-C est de 105° alors que celui entre C-O-C est de
121°.5 Cette différence substantielle dans les angles de liaison réduirait la densité
d’empilement des chaînes. Ceci entraîne une diminution de l'enthalpie de fusion et de
la température de fusion (Tm).6 En conséquence, l'intervalle (Tm-Tg) est assez étroit
et la cristallisation est inhibée.
2
Dans cette même famille de polymères, on rencontre le polysulfone (PSF) et le
poly(phényl sulfone) (PPSF) qui ont été commercialisés sous différents noms (voir le
Tableau 1.1) et le poly(éther éther sulfone) (PEES).
Tableau 1.1 : Famille des polyéthersulfones avec leurs abréviations, structures
chimiques, noms commerciaux, producteurs et années de synthèse1
Abréviations Structures chimiques Noms Producteurs Années
PES
Victrex ICI 1972
PSF
Udel UCC 1965
PPSF
Radel UCC 1976
PEES
- - -
1.1 Revue de la littérature sur la synthèse des PES
Les PES ont été synthétisés pour la première fois et de façon indépendante dans les
années 1960 par trois (3) laboratoires différents que sont : 3M Corporation7 et Union
Carbide Corporation (UCC),8,9 tous deux basés aux États-Unis et le Plastics Division
of ICI10 basé au Royaume Uni. L’objectif était de développer des matériaux
thermoplastiques thermiquement stables répondant à des applications d'ingénierie.11,12
Deux principales méthodes ont été utilisées pour la synthèse des PES. 3M
Corporation a synthétisé les PES par polysulfonylation du 4,4'-
bis(chlorosulfonyl)diphényle éther avec l’oxydibenzène en utilisant une réaction de
Friedel-Crafts,12 tel que montré dans le schéma 1.2, autrement dit en utilisant une
3
substitution électrophile aromatique.1 Cependant, cette méthode est peu sélective et
souffre d’une faible réactivité pour un tel substrat.13 Union Carbide Corporation,
quant à elle, a développé les PES par polyétherification en utilisant une réaction de
substitution nucléophile aromatique12 (Schéma 1.3). ICI a également utilisé la
substitution nucléophile aromatique pour la synthèse de ces polymères mais en
faisant réagir un sel de métal alcalin d’un composé 4-chloro-4’-hydroxy diphényl
sulfone sur lui-même pour obtenir un PES (Schéma 1.3a) ou bien un diphénolate de
métal alcalin avec un composé bis(4-chlorophényl) sulfone pour obtenir un PEES
(Schéma 1.4), en utilisant un solvant polaire aprotique comme le diméthyle sulfoxyde
(DMSO).1,6 Cependant, un léger excès de NaOH conduit à un clivage des chaînes du
polymère, ce qui entraîne l’obtention de polymères de faibles masses molaires.14 Par
la suite, des masses molaires élevées ont été obtenues en remplaçant le NaOH par le
K2CO3 en présence d’un solvant polaire aprotique de haut point de fusion comme le
sulfolane ou le diphényle sulfone mais à une température très élevée (335 °C).14,15
Schéma 1.2 : Synthèse des PES par polysulfonylation utilisée par 3M Corporation12
4
Schéma 1.3 : Synthèse des PES par polyétherification utilisée par Union Carbide
Corporation et ICI12
Schéma 1.4 : Synthèse des PEES par polyétherification utilisée par Plastics division
of ICI12
Les solvants polaires aprotiques, en plus de faciliter la solubilité du polymère,
permettent d’augmenter la nucléophilie de l’alcoolate en complexant les cations Na+
ou K+ si l’hydroxyde de potassium est utilisé à la place de l’hydroxyde de sodium,
augmentant ainsi le degré de dissociation.8 Les atomes d’halogène de ces composés
sont activés par le groupe sulfone (groupement fortement électro-attracteur) situé en
position para par rapport à l’halogène.8
La principale méthode utilisée pour la synthèse des PES est donc la polycondensation
par substitution nucléophile aromatique. Le mécanisme de substitution nucléophile
aromatique est présenté dans le Schéma 1.5. Dans un premier temps, le nucléophile
attaque le carbone porteur de l’halogène (C-X) activé par le groupement sulfone
(groupement fortement électroattracteur). L’halogène X ne part pas directement mais
il y a création d’un intermédiaire stabilisé par résonance appelé complexe de
5
Meisenheimer.12 La deuxième étape de réaction consiste à l’élimination du groupe
partant, X.
Les composés fluorés sont plus réactifs que les composés chlorés correspondants qui,
eux, sont plus réactifs que leurs analogues bromés car plus l’halogène est
électronégatif mieux il stabilise la charge négative de l’intermédiaire réactionnel
(complexe de Meisenheimer). L’attaque du nucléophile, dans le cas des composés
fluorés, est également favorisée par le caractère non volumineux (donc moins
encombrant) des atomes de fluor et la forte polarisation du lien Cδ+-F δ- due à leur
forte électronégativité qui augmente le caractère électrophile de l’atome de carbone.12
Schéma 1.5 : Mécanisme de substitution nucléophile aromatique
1.2 Les réactions thiol-ène clic radicalaires
Le terme chimie clic, introduit en 2001 par Sharpless et al.,16 décrit des couples de
groupements fonctionnels réagissant rapidement et sélectivement l’un avec l’autre
dans des conditions douces. Ces réactions chimiques ont pour caractéristiques d’être à
la fois modulables, régiosélectives, efficaces donnant des produits facilement
purifiables (isolation simple et non chromatographique de l’adduit obtenu) avec des
rendements élevés.16,17
Le terme thiol-ène clic est utilisé pour désigner l'addition d'un thiol sur une liaison
ène (double liaison).18 Les réactions thiol-ène clic radicalaires sont des réactions
photochimiques c’est-à-dire qui se déroulent sous l'action de la lumière. Les réactions
6
thiol-ène clic radicalaires ont l’avantage de combiner les attributs de la chimie clic et
d'une réaction photoamorcée (activation à des moments et des endroits spécifiques),
ce qui fait qu’elles sont des méthodes intéressantes pour la synthèse chimique de
matériaux avec des propriétés modulables.19,20 Ces réactions sont donc largement
utilisées dans les domaines des biosciences,21,22 de la chimie médicinale23 et de la
chimie des matériaux.24 Dans la chimie des matériaux polymères, elles sont utilisées
pour faire une polymérisation, une modification de surface, un greffage de molécules
ou bien pour synthétiser des dendrimères.25 Comme pour tout procédé radicalaire, il
existe un certain nombre de moyens d'initiation des réactions thiol-ène clic. Ces
méthodes d’excitation sont largement discutées par Hoyle et al.20 Nous nous
limiterons au procédé d'excitation par clivage homolytique d’un photoiniateur comme
le 2,2-diméthoxy-2-phénylacetophénone (DMPA) qui est l’un des plus efficaces car
le rendement quantique pour la production de radicaux réactifs est plus élevé.20 Par
irradiation avec une lampe à rayons ultraviolets (UV) de longueur d’onde 365 nm, le
DMPA se clive facilement en générant deux radicaux A (radical benzoyle) et B
(radical (diméthoxyméthyl) benzène) (Schéma 1.6). Le radicale B se réarrange pour
former un radical méthyle et le benzoate de méthyle.20,26 Les radicaux A et méthyle
ont une affinité très grande pour l’hydrogène et donc peuvent facilement arracher un
hydrogène d’un thiol donnant naissance à un radicale thiyle très réactif.27 Le radical
thiyle formé réagit ensuite avec la double liaison dans une configuration anti-
Markovnikov pour donner un thiolalkyle radical. Ce dernier capte un hydrogène d’un
thiol conduisant ainsi à la formation d’un thioéther et d'un nouveau radical thiyle qui
peut réagir de nouveau avec une double liaison (Schéma 1.7).18,25,27
7
Schéma 1.6 : Mécanisme radicalaire du DMPA26
Schéma 1.7 : Mécanisme de la réaction thiol-ène clic18,25,27
1.3 Domaine d’application des PES
Les polyéthersulfones (PES) et polyétheréthersulfones (PEES), avec un éther de plus
(Tableau 1.1), sont des polymères qui suscitent un grand intérêt dans la fabrication de
dispositifs de haute technologie non seulement du fait de leur haute performance
thermique, chimique et radiative6,28,29 mais également de la possibilité pour le
chimiste de modifier les propriétés chimiques et physiques de ces polymères pour les
8
adapter à des besoins particuliers. Les dispositifs constitués par ces matériaux ont un
excellent comportement mécanique face aux températures élevées, ils sont également
très résistants aux chocs, au feu et à l’hydrolyse.30-32 La principale application de ces
polymères réside dans la fabrication de membranes pour la filtration. Les
polyéthersulfones sont d’excellents candidats pour la fabrication de membranes pour
la microfiltration ou l’ultrafiltration car :33,34
- ils permettent d’avoir une grande sélectivité de la membrane (taux de rejet élevé)
et une bonne distribution de la taille des pores ;
- ils sont très résistants à l’oxydation par les désinfectants tels que les peroxydes ou
l'hypochlorite souvent nécessaires pour le nettoyage des membranes après
utilisation ;
- ils présentent un excellent comportement thermique, résistant jusqu’à 400 °C, avec
des températures de transition vitreuse qui atteignent les 200 °C4 due à la rigidité
intrinsèque de la chaîne (présence de noyaux aromatiques)3,4,35 et peuvent être
utilisés sur un large domaine de pH ;
- ils possèdent des propriétés mécaniques intéressantes qui permettent de résister
aux gradients de pression utilisés comme force motrice de transfert lors des
opérations de filtration.
Les premières membranes à base de PES ont été obtenues avec le polysulfone (PSF)
au cours des années 1960 pour une alternative aux membranes cellulosiques dans des
procédés de séparation, en raison de leur résistance très élevée dans des conditions
extrêmes de pH et une bonne stabilité thermique.36 De nos jours, les applications
existantes se situent principalement dans la fabrication de membranes pour des filtres
de seringue utilisés pour la filtration de solutions à l’échelle du laboratoire ou bien
pour des applications dans le domaine industriel pour des membranes à fibres creuses.
Dans l’industrie laitière, par exemple, ces membranes ont permis de valoriser le
coproduit majeur dans la fabrication du fromage, le lactosérum communément appelé
petit lait (Figure 1.1). Le lactosérum a été considéré pendant longtemps comme
9
déchet dans l’industrie fromagère, mais aujourd’hui, grâce à ces membranes, il est
possible de le fractionner en plusieurs constituants individuels de haute qualité
nutritive (concentrés de protéines, isolats de protéines, …).
Figure 1.1 : Filtration du lait caillé pour la production du fromage
(adapté à partir de la page web du Comité de défense du véritable camembert,
http://veritable.camembert.free.fr/pages/Lait_traitements.htm, consultée le 17 janvier
2016)
On se sert également de ces membranes de PES pour la production industrielle d’eau
potable, à travers un procédé sûr, efficace et rapide pour l'élimination des particules,
de la turbidité et des micro-organismes présents dans l'eau.
Les deux niveaux de filtration membranaire les plus utilisés pour les PES sont la
microfiltration et l’ultrafiltration.1,37,38
La microfiltration, pour laquelle la taille des pores de la membrane est de l’ordre du
micromètre et se situant généralement entre 0,1 à 10 μm, permet d’éliminer les
matières en suspension et de faire l’épuration bactérienne.
L’ultrafiltration, avec une taille des pores de la membrane variant de 1 à 100 nm, en
plus de l’épuration bactérienne, permet d’éliminer les virus.
10
D’autre part, il est possible de moduler les propriétés de ces polymères pour les
adapter à une application bien définie en greffant certains groupements sur la chaîne
polymère.7,14 Les polyéthersulfones dont des groupements sulfones sont rajoutés sur
les cycles aromatiques sont utilisés comme membranes échangeuses d’ions dans les
piles à combustible pour des applications dans le domaine du transport (véhicules,
camions, autobus et locomotives) et l'électronique.39,40
Du fait de la résistance de ces matériaux à l’eau et à la vapeur, ils sont utilisés pour
fabriquer des ustensiles de cuisson et du matériel médical (nébuliseurs et composants
de dialyse).1 Ils ont aussi des applications dans le domaine nucléaire, des
télécommunications, des pièces automobiles ou aérospatiales pour l’isolation de
câbles.14
1.3.1 Filtration membranaire
Une membrane de filtration est un matériau à perméabilité sélective qui permet de
séparer des particules en solution en fonction de leur taille sous l'action d'une force
motrice, le but étant de purifier un liquide ou de fractionner ou concentrer des
particules. Les particules retenues au niveau de la surface de la membrane forment le
rétentat tandis que celles qui la traversent représentent le perméat (Figure 1.2).
Figure 1.2 : Principe d’une membrane de filtration selon Prulho41
11
Il existe deux modes de filtration, les filtrations frontale et tangentielle, que l’on
différencie selon l’orientation du flux d’alimentation.
En mode frontal (filtration la plus connue), le flux d’alimentation est perpendiculaire
à la membrane alors que dans le cas d’une filtration tangentielle, le flux arrive
parallèlement à la membrane. La tangentielle permet un colmatage moins rapide, mais
elle est généralement réservée à la filtration de très petites particules.
La majorité des membranes polymères poreuses commercialisées sont
élaborées via un procédé de séparation de phases. La séparation de phases (également
appelée inversion de phase ou démixtion) résulte d'un changement d'état
thermodynamique d'une solution de polymère initialement homogène. Le changement
d'état thermodynamique peut être induit par différentes méthodes :42
- variation de la température ;
- intrusion d'un non-solvant dans une solution binaire polymère/solvant.
Tous les processus de séparation de phases sont basés sur les mêmes principes
thermodynamiques. Dans tous les cas, le point de départ est une solution
thermodynamiquement stable soumise ensuite à des conditions entraînant une
démixtion telle qu'un abaissement de température ou l'intrusion d'un non-solvant.
L'inversion de phase induit la création de deux phases : une phase pauvre et une
phase riche en polymère qui croissent suivant des mécanismes de nucléation-
croissance pour former l'architecture membranaire.42 Après démixtion liquide-liquide,
la phase riche en polymère se solidifie et constitue alors la matrice membranaire. La
phase pauvre est éliminée par des lavages successifs et laisse place aux pores de la
membrane.
1.4 Problématique
Les polyéthersulfones sont utilisés dans plusieurs domaines, cependant l’obtention de
voies de synthèse permettant un meilleur contrôle de leur masse moléculaire, leur
morphologie et leurs propriétés thermiques reste toujours un défi pour les chercheurs.
12
La polycondensation par substitution nucléophile aromatique est la principale
méthode utilisée pour la synthèse des PES. Cette polycondensation est effectuée en
système ouvert en déplaçant l'équilibre de la réaction par élimination de la petite
molécule formée lors de la réaction. Cette élimination devient de plus en plus difficile
au fur et à mesure que la réaction avance du fait de la vitesse de diffusion de ces
petites molécules, ce qui rend peu probable les possibilités de contrôle de la masse
molaire. Ce type de polymérisation ne permet pas, non plus, de contrôler la
morphologie et les propriétés thermiques. Le contrôle de ces paramètres pourrait
jouer un rôle déterminant dans l’amélioration des propriétés pour des applications
déjà existantes, mais pourrait aussi permettre de répondre à des besoins additionnels,
notamment la modulation des propriétés séparatrices des membranes.
La principale application des PES se situe dans la fabrication de membranes,
cependant leur utilisation comme membranes est souvent limitée par leur caractère
hydrophobe qui, par l’adsorption de particules au niveau de la surface, entraîne un
encrassement de la membrane conduisant ainsi au colmatage.28,43 Le colmatage
résulte de l’accumulation des substances filtrées au niveau de la surface de la
membrane ou à l’intérieur des pores et, entraîne une perte des performances des
membranes. Les causes du colmatage des membranes à base de PES peuvent
provenir de trois origines principales :44
- Le colmatage par adsorption : Il provient de la fixation de particules au niveau
de la surface de la membrane et résulte en général des interactions entre les
molécules notamment les protéines que contiennent les liquides filtrés et les
surfaces hydrophobes de la membrane. Le degré d'adsorption dépend du type
d'interaction tel que les liaisons hydrogène, les interactions dipolaires, les
interactions de van der Waals, et les effets électrostatiques.45 Cependant, il a été
rapporté que les interactions hydrophobes sont le principal facteur renforçant
l'adsorption des protéines sur la surface des membranes à base de
polyéthersulfone.46 Quand une molécule de protéine est en contact avec la surface
d’une membrane hydrophobe, les molécules d'eau liées à la protéine vont se
déplacer du fait des interactions hydrophobes. Ceci provoque une rupture de la
13
liaison entre la protéine et les molécules d’eau, induisant des changements de
conformation dans la structure de la protéine, ce qui se traduit par une adsorption
irréversible de la protéine sur la surface de la membrane.47,48
- La capture de particules : Elle intervient lors de la filtration uniquement et se
caractérise par le blocage de particules dans les pores de la membrane par effet
stérique sous l’effet de la force motrice.49
- La création de biofilms : Elle intervient lorsque des bactéries se développent à la
surface de la membrane sous l’effet de conditions favorables à leur développement
(température notamment), et en particulier dans les zones de faibles convections.
Les bactéries sécrètent des exopolymères qui forment un film peu perméable
recouvrant la surface de la membrane.
Des observations réalisées par le groupe de Qilin Li50 au microscope électronique à
balayage (MEB) ont permis de mettre en évidence la présence d’un agrégat de
particules à la surface de la membrane après ajout de particules organiques dans les
solutions filtrées (Figure 1.3). Ce dépôt de matières organiques, adhérant au matériau
membranaire, induit des chutes importantes du flux de perméation et, en raison de
leur croissance, il est difficile de les éliminer par la suite. Un rétrolavage à l’eau
seulement n’est plus suffisante pour retrouver la perméabilité optimale de la
membrane. Un nettoyage chimique est donc nécessaire. Par exemple, la soude
caustique associée à de l’hypochlorite de sodium (NaClO/NaOH) permet de
solubiliser la matière organique composée de groupement phénol ou carboxyle et
dégrader les polysaccharides et protéines en sucres et composés aminés plus
petits.51,52 Les lavages acides permettent d’éliminer des espèces cationiques.53
L’impact des lavages chimiques sur l’intégrité membranaire est encore peu étudié,
cependant il a été montré qu’à long terme ces lavages chimiques peuvent entraîner
une modification du matériau membranaire et aggraver le colmatage.54
14
Figure 1.3 : Images MEB en coupe plane (a) et transversale (b) d’une membrane
colmatée (agrégat de particules encerclé en vert) 50
Pour réduire cet effet, il est rapporté dans la littérature qu’il faudrait augmenter
l’hydrophilicité de ces polymères pour améliorer les propriétés anti-adsorbantes des
membranes, ce qui limitera considérable le colmatage et ainsi maintenir les
performances de la membrane.48,55,56
Il est également rapporté que les membranes hydrophiles sont plus faciles à nettoyer
que les membranes hydrophobes car l’adsorption devient faible et donc facile à
enlever.
Une des stratégies visant à améliorer l'hydrophilicité de ces polymères est de les
mélanger avec d’autres polymères hydrophiles comme les polyéthylènes glycols
(PEG), mais cette méthode a des limites car à un certain rapport massique, la solution
de polymère devient hétérogène conduisant à la séparation de phases lors de la
fabrication de la membrane. Le groupe de Mohammadi57 a montré qu’en mélangeant
le PES avec le polyacrylonitrile (PAN) dans un rapport massique de 70/30, il apparaît
deux couches au niveau de la membrane vue au microscope électronique à balayage
(MEB) due à la séparation de phase lors de sa fabrication (Figure 1.4). Cette
séparation modifie considérablement la structure de la membrane, comparée à celle
du PES.
Coupe plane Coupe transversale
a) b)
15
Figure 1.4 : Images MEB d’une coupe transversale d’une membrane de PES seul (a)
et d’un mélange PES/PAN dans un rapport massique 70/30 (d), telles que publiées
par Amirilargani et al.57
Pour les piles à combustible, le rajout des groupements sulfones sur les noyaux
aromatiques pose souvent un problème de stabilité. Zhang et al.40 ont rapporté qu’il
est généralement considéré que les polymères avec des groupes acides sulfoniques
pendants ou des chaînes latérales sont plus stables à l'hydrolyse que ceux avec des
groupes acides sulfoniques directement connectés sur le squelette des polymères.
I.5 Objectif du projet
Dans cette présente étude, notre objectif est de synthétiser les PES avec incorporation
de segments flexibles comportant des doubles liaisons dans les chaînes du polymère
pour contrôler :
- la cristallinité ;
- les températures de transition vitreuse ;
- l’hydrophilicité des copolymères obtenus.
La modulation de la cristallinité est effectuée en introduisant, au sein de la chaîne, un
groupement allyl flexible, de configuration cis ou de configuration trans. Ces
segments flexibles pourraient provoquer un repliement de chaînes à l’image des
travaux du groupe de Josée Brisson58 sur des copolymères rigides flexibles de Kevlar
où il est indiqué que la présence d’une chaîne flexible permet le repliement des
chaînes de polymères rigides, mais pourraient aussi, si le bloc rigide est de taille assez
faible, être incorporés au sein de l’unité de répétition et de la maille cristalline. Le
16
changement de configuration permettra alors d’obtenir une chaîne de symétrie et de
conformation différentes, ce qui devrait provoquer le changement de cristallinité
désiré.
Les températures de transition vitreuse sont contrôlées par la modulation du
pourcentage de segment flexible incorporé dans les chaînes du polymère.
Les doubles liaisons incorporées sont utilisées pour une post-fonctionnalisation,
permettant de contrôler l’hydrophilicité enfin d’adapter les propriétés des
copolymères à des applications bien définies. Par exemple, pour lever les contraintes
d’application des PES (leur caractère hydrophobe) dans les membranes de filtration,
leur hydrophilicité est modulée en fonctionnalisant les copolymères obtenus à travers
les doubles liaisons incorporées par le greffage de différentes molécules hydrophiles.
L’ajout des segments flexibles permettra éventuellement d’améliorer la solubilité de
ces matériaux et de faciliter leur mise en œuvre.59 Cependant, leur ajout provoque une
baisse des températures de transition vitreuse.59 C’est pourquoi la séquence, la taille
et la proportion de ces segments flexibles doivent être ajustées afin de minimiser leurs
effets sur les propriétés thermiques des matériaux résultants.
Pour l’introduction des segments flexibles dans les chaînes du polymère, une
méthodologie appropriée doit être utilisée pour arriver à l’objectif fixé. Deux
approches différentes sont donc utilisées dans ce projet : la polymérisation par
métathèse des diènes acycliques (ADMET en anglais, Acyclic Diene Metathesis
Polymerization) et la polycondensation classique.
La polymérisation par métathèse des diènes acycliques (ADMET) permet d’obtenir
des polymères de faibles polydispersités avec des doubles liaisons régulièrement
réparties le long des chaînes du polymère.
La polycondensation, elle, permet d’obtenir directement des copolymères de
configuration cis ou trans avec incorporation régulière ou aléatoire des doubles
liaisons.
17
1.6 Méthodologie
1.6.1 Polymérisation par métathèse des diènes acycliques (ADMET)
Dans la science des matériaux, la métathèse des oléfines permet, entre autres, de faire
des réactions de polymérisation par métathèse de diènes acycliques plus connues sous
le nom de ADMET (en anglais : Acyclic Diene Metathesis Polymerization).60 Ces
réactions de polymérisation sont rendues possibles par l’usage d’un certain type de
catalyseurs carbéniques qui peuvent différer par la nature du métal central (titane,
molybdène, tungstène, ruthénium).61 Cependant, un choix approprié du catalyseur est
important pour éviter les réactions secondaires indésirables qui peuvent avoir lieu
entre le catalyseur et les groupements fonctionnels du milieu réactionnel. Ces derniers
peuvent se lier avec le centre actif du métal et ainsi désactiver complètement le
catalyseur.62 Le succès de la polymérisation par métathèse des oléfines repose donc
sur l’usage de catalyseurs qui réagissent préférentiellement avec des oléfines en
présence de groupements fonctionnels hétéroatomiques.
Une étude permettant de suivre la réactivité des catalyseurs à base de titane,
tungstène, molybdène et ruthénium vis-à-vis des oléfines en présence d’autres
groupements fonctionnels a montré que ceux formés de ruthénium sont beaucoup
plus sélectifs aux oléfines qu’aux autres groupements fonctionnels présents dans le
milieu réactionnel.62
18
Tableau 1.2: Réactivité des catalyseurs à base de titane, tungstène, molybdène et
ruthénium vis-à-vis des oléfines en présence de groupements fonctionnels
hétéroatomiques62
Titane Tungstène Molybdène Ruthénium
Acides Acides Acides Oléfines
Ordre de
réactivité
des
oléfines
Alcools, Eau Alcools, Eau Alcools, Eau Acides
Aldéhydes Aldéhydes Aldéhydes Alcools, Eau
Cétones Cétones Oléfines Aldéhydes
Esters, Amides Oléfines Cétones Cétones
Oléfines Esters, Amides Esters, Amides Esters, Amides
De cette étude, dont les résultats sont résumés dans le Tableau 1.2, on conclut que les
catalyseurs au titane, tungstène et molybdène sont plus disposés à réagir avec les
groupements acides, alcools, eau, et aldéhydes qu’avec les oléfines alors que ceux à
base de ruthénium sont plus sélectifs aux alcènes.
Hormis le choix du catalyseur, le choix d’un bon solvant s’impose pour cette
polymérisation. Schulz et al.63 ont indiqué que la réussite de cette polymérisation
dépend de la capacité du solvant à :
- initier le catalyseur ;
- augmenter la réactivité des espèces actives du catalyseur et du substrat ;
- maintenir l’activité du catalyseur pour un temps plus ou moins long.
Ce groupe a effectué la polymérisation par métathèse des diènes acycliques dans
différents solvants (Figure 1.5) en utilisant les catalyseurs de Grubbs deuxième
génération et Hoveyda – Grubbs. L’étude a révélé que les réactions effectuées dans le
dichlorométhane présentaient les masses molaires les plus élevées.
19
Figure 1.5 : Comparaison des masses molaires obtenues par ADMET avec les
catalyseurs de Grubbs deuxième génération et Hoveyda – Grubbs dans différents
solvants63
Dans le cadre du présent projet, deux types de catalyseurs à base de ruthénium ont été
utilisés : le Grubbs deuxième génération (G2) et le Hoveyda-Grubbs (HG) (Schéma
1.8). Ces catalyseurs sont, non seulement plus tolérants aux groupes fonctionnels
présents dans le milieu réactionnel, mais aussi plus actifs et plus stables en présence
d’air et d’humidité.62,64-67 Le dichlorométhane a été sélectionné comme solvant.
Schéma 1.8 : Catalyseurs de Grubbs utilisés pour l’ADMET
20
Pour ce type de polymérisation, le catalyseur réagit avec une oléfine pour la
formation du polymère. Il est donc important de trouver une architecture appropriée
pour le monomère pour que la réaction ait lieu (Schéma 1.9). Ainsi, des groupements
allyliques ont été connectés aux deux bouts d’une macromolécule à base
d’éthersulfones qu’on appellera par la suite, bloc rigide, tel qu’illustré dans le Schéma
1.9.
Schéma 1.9: Polymérisation par métathèse des diènes acycliques (ADMET)
Le mécanisme de polymérisation par métathèse de diènes acycliques est bien connu
et, est composé de cinq (5) étapes principales, tel qu’illustré dans le Schéma 1.10. La
réaction commence par une liaison de coordination entre l’oléfine et le métal central
du catalyseur (1), suivie de la formation d’un intermédiaire métallacyclobutane (2).
Le clivage productif de cet intermédiaire conduit à la formation d’un complexe
alkylidène actif (3) qui peut réagir avec un diène pour former un autre complexe
métallacyclobutane (4). Celui-ci se clive à son tour pour donner le polymère. Le
catalyseur est régénéré et peut réagir de nouveau avec un autre diène ou un polymère
en croissance pour former encore un complexe métallacyclobutane (5) dont le clivage
conduit à la formation d’un nouveau complexe alkylidène avec dégagement de
l’éthylène, et puis la réaction se poursuit.
21
Schéma 1.10 : Mécanisme de polymérisation par métathèse des diènes acycliques
(ADMET)69,70
Les blocs rigides sont synthétisés dans ce projet par substitution nucléophile
aromatique qui reste le procédé approprié pour synthétiser les éthersulfones14 du fait
de sa régiospécificité.68 Ce type de réaction nécessite l'utilisation de solvants polaires
aprotiques tels que le diméthylsulfoxide ou le N,N-diméthylacétamide qui augmentent
l’activité de la base par une solvatation importante du contre-cation.
1.6.2 Polycondensation
La polymérisation par métathèse des diènes acycliques (ADMET) ne permet pas
d’introduire les segments flexibles dans les chaînes du polymère de façon aléatoire.
Elle ne permet pas, non plus, de diminuer la concentration de ces segments flexibles
dans les chaînes du polymère au moment de la polymérisation, ce qui fait qu’on
obtient des copolymères dont la rigidité n’est pas assez importante pour compenser
22
l’effet des segments flexibles sur les températures de transition vitreuse. La
polycondensation permet non seulement, de contourner cet effet mais aussi de
synthétiser directement des copolymères de configuration cis ou trans ayant des
propriétés différentes (solubilité, cristallinité, propriétés thermique) en faisant réagir
respectivement un monomère flexible de configuration cis ou trans avec un bloc
rigide à base d’éthersulfone (Schéma 1.11). On sauve également une étape dans la
synthèse du monomère (bloc rigide), car on n’a pas besoin de connecter les
groupements allyliques en bouts de chaîne.
Le rapport bloc rigide/segment flexible peut donc être contrôlé dans le cas de la
polycondensation, ce qui permet de moduler les températures de transition vitreuse
(Tg) des copolymères résultants. L’utilisation de monomères flexibles de
configuration cis ou trans permet également de contrôler la cristallinité des
copolymères.
Un avantage de la polycondensation vient de la grande variété des monomères
utilisables, ce qui permet d’ajuster les propriétés des polymères selon l’application.
Cependant, il est important d’avoir un mélange équimolaire entre les monomères
pour obtenir de hautes masses. Les indices de polydispersité sont également plus
élevés dans une réaction de polycondensation que dans une ADMET.
Schéma 1.11: Illustration de la polycondensation entre un bloc rigide et un segment
flexible
1.6.3 Caractérisation des polymères
Les copolymères obtenus par ces deux approches sont ensuite caractérisés
principalement par résonance magnétique nucléaire (RMN) et spectroscopie
infrarouge à transformée de Fourier (FTIR) pour l’identification, chromatographie
23
d’exclusion stérique (SEC) pour évaluer les masses molaires, analyse
thermogravimétrique (TGA) pour déterminer les températures de dégradation,
calorimétrie différentielle à balayage (DSC) pour obtenir les températures de
transition vitreuse et de fusion et par diffraction des rayons x pour l’étude de la
cristallinité.
La spectrométrie de masse MALDI-TOF (Matrix-Assisted Laser
Desorption/Ionisation - Time Of Flight, en français : désorption/ionisation laser
assistée par matrice - temps de vol) est utilisée pour montrer que l’incorporation des
segments flexibles dans les chaînes du polymère se fait de manière aléatoire ou s’il y
a création de blocs polymères par réaction préférentielle d’un des monomères au
début de la réaction. Nous allons donner une brève description de cette méthode qui
est de plus en plus utilisée pour caractériser les polymères.
La spectrométrie de masse est une technique d'analyse physico-chimique permettant
de détecter, d'identifier et de quantifier des molécules d’intérêt par mesure de leur
masse. Son principe réside dans la séparation en phase gazeuse de molécules chargées
(ions) en fonction de leur rapport masse/charge (m/z).
Le spectromètre de masse MALDI-TOF est un spectromètre utilisant une source
d’ionisation laser assistée par une matrice et un analyseur à temps de vol. C’est une
technique d'ionisation douce (ionisation sans fragmentation) qui permet l'analyse
de biomolécules (des biopolymères comme les protéines, les peptides et les sucres) et
les grosses molécules organiques (comme les polymères, les dendrimères et
autres macromolécules) sensibles à la chaleur sans se dégrader.
L’échantillon à analyser est dispersé dans une matrice qui permet de faciliter sa
vaporisation et son ionisation. La matrice est une molécule qui a une pression de
vapeur assez grande afin de ne pas s'évaporer sous un certain vide et durant la
préparation de l'échantillon, une faible masse moléculaire pour faciliter la
vaporisation, une forte absorption dans l'ultraviolet, lui permettant d'absorber
24
efficacement et rapidement l'irradiation laser. Elle doit aussi être soluble dans un
solvant approprié aux molécules étudiées.
Pour les PEES, on utilise généralement le dithranol ou bien le trans-2-[3-(4-tert-
butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) comme matrice.71
Un agent cationisant comme des ions Na+ ou Li+ est ajouté au mélange
(échantillon/matrice). L’ensemble est co-cristallisé sur une plaque MALDI par
évaporation du solvant. L'ionisation, qui s’effectue dans la chambre d’ionisation, est
provoquée par irradiation sous vide du dépôt solide par des impulsions laser de
longueur d’onde où la matrice présente une forte absorption. Il en résulte une
désorption puis une désolvatation avec transfert de proton (H+) de la matrice
photoexcitée aux molécules de l’échantillon analysé. L’ionisation des molécules de
l’échantillon se produit principalement par transfert de protons à partir de la matrice
et il se forme l’ion moléculaire [M+H]+. Des molécules sont également ionisées par
l’addition de l’agent cationisant pour former l’ion moléculaire [M+cation]+.
Cependant, il y a controverse sur la formation de ces ions.72 Knochenmuss et al.73
mettent en jeu la réaction ion-molécule dans le nuage formé par la désorption de
l’échantillon et Frankevich et al.74 indiquent que les électrons proviennent non pas de
la matrice photoionisée mais du support métallique de l’échantillon.
Les ions moléculaires générés sont accélérés dans un champ électrique et pénètrent
dans l’analyseur à temps de vol (tube de vol) où ils sont séparés en fonction de leur
temps de vol qui est proportionnel au rapport m/z (m/z = 2U. t2/L2 avec U = tension
appliquée, t = temps de vol, L = longueur du tube de vol).
Plus un ion monochargé sera lourd, c’est-à-dire plus son rapport m/z sera élevé, plus
il va mettre plus de temps pour arriver au détecteur.
Le détecteur transforme le courant ionique en courant électrique permettant d’obtenir
un spectre de masse caractérisant l’échantillon.75-77
La technique MALDI_TOF produit de manière générale des ions moléculaires
monochargés, mais des ions multichargés ([M+nH]n+) peuvent aussi être observés,
selon la matrice utilisée et/ou l'intensité du laser.
25
Schéma 1.12: Principe de fonctionnement d’un spectromètre de masse MALDI-
TOF.72
Les spectres de masse MALDI-TOF peuvent être obtenus en mode linéaire ou
réflectron selon l’équipage de l’appareil.
En mode linéaire, le temps de vol des ions moléculaires est plus court (Figure 1.6) et
la résolution des pics du spectre est plus faible.72 Les ions de même rapport m/z
peuvent arriver au détecteur à des moments différents dû au fait qu’ils n’ont pas la
même énergie cinétique (donc qu’ils ont des vitesses différentes) à l’entrée de
l’analyseur, ce qui a pour conséquence d’élargir les pics du spectre obtenu.
En mode réflectron, le spectromètre MALDI-TOF est équipé d’un réflectron (Figure
1.6), encore appelé miroir électrostatique, qui a pour but de dévier le faisceau ionique
Représentation des
données dans un spectre
de masse
Séparation des ions
produits en fonction du
rapport m/z
Production d’ions en
phase gazeuse
Conversion du courant
ionique en courant
électrique
Chambre
d’ionisation
Analyseur à temps
de vol
Détecteur
Traitement du
signal
26
avec un champ électrique, de regrouper les ions de masse similaire et de les diriger
vers un second tube de vol qui les conduit vers un second détecteur.
Pour des ions ayant le même rapport m/z mais des énergies cinétiques différentes,
l’ion le plus rapide va entrer plus profondément dans le miroir électrostatique. Il va
parcourir alors une plus grande distance et passera plus de temps dans le réflectron
que l’ion le plus lent. Ce phénomène conduit à une arrivée simultanée des ions de
même rapport m/z au niveau du détecteur malgré leur différence de vitesse de départ,
ce qui augmente la résolution des pics des spectres obtenus.
Figure 1.6: Composants basiques d’un spectromètre MALDI-TOF utilisable en mode
linéaire et mode réflectron72
L’étalonnage en masse de l’appareil MALDI s’effectue à l’aide de calibrants dont les
masses molaires encadrent les valeurs de m/z des molécules d’intérêt.
Cette technique est, cependant, limitée par la masse et la volatilité des molécules
analysées et par les limites physiques des détecteurs utilisés.75
Matrice/échantillon
Détecteur en
mode réflectron
Détecteur en
mode linéaire
Réflectron
Ions
Source Laser
27
1.6.4 Post-fonctionnalisation des copolymères
La post-fonctionnalisation a pour but de moduler l’hydrophilicité des copolymères et,
est effectuée en utilisant les réactions thiol-ène clic. La méthode consiste à irradier la
solution par la lumière d’une lampe à rayons ultraviolets (UV) de longueur d’onde
365 nanomètres, nécessaire pour la formation du radical photoinitiateur utilisé dans
ce travail, le 2,2-diméthoxy-2-phénylacetophénone (DMPA). Après échange de
proton avec le radical photoinitiateur, le radical thiol formé réagit avec une double
liaison pour donner le copolymère fonctionnalisé. Les différentes molécules
commerciales utilisées pour la post-fonctionnalisation sont sélectionnées suivant les
groupements fonctionnels hydrophiles qu’ils contiennent. Ainsi des polyéthylènes
glycols (PEG) de faibles et de hautes masses molaires sont utilisés (voir chapitre 4).
Des molécules hydrophobes sont également utilisées dans ce travail à titre de
comparaison.
1.6.5 Mesures d’angle de contact
Après la post-fonctionnalisation, des mesures d’angles de contact sont effectuées pour
évaluer l’hydrophilicité des copolymères.
La mesure d'angle de contact rend compte de l'aptitude d'un liquide à s'étaler sur une
surface par mouillabilité.
La méthode consiste à mesurer l'angle de la tangente du profile d'une goutte avec la
surface du substrat sur laquelle elle est déposée.
En utilisant l'eau comme liquide de mesure d'angle de contact, on peut déduire le
caractère hydrophobe (grand angle, faible énergie de surface, faible mouillabilité) ou
hydrophile (petit angle, grande énergie de surface, bonne mouillabilité) de la surface
(Figure 1.7).
28
Figure 1.7: Mesure de l’angle de contact
(adapté à partir de University of Western Ontario,
http://www.eng.uwo.ca/zeolite/Goniometer.htm, consulté le 17 janvier 2016)
En pratique, une goutte de liquide, en général de l’eau ultra-pure, est déposée à l’aide
d’une seringue sur une surface de l’échantillon à analyser éclairée par une source
lumineuse et à l’aide d’une caméra, tout étant contrôlé par ordinateur (Figure 1.8).
29
Figure 1.8: Principe de mesure de l’angle de contact
(adapté à partir de http://www.biophyresearch.com/technique-analyse/angles-de-
contact/ consulté le 17 janvier 2016)
En mesurant l’hystérèse (différence des angles d’avancement et de retrait de la
goutte), on obtient des renseignements sur l’homogénéité de la surface.
En faisant une série de mesures d’angles de contact avec différents liquides de
tensions superficielles connues (eau, glycérol éthylène glycol, diiodométhane, etc.),
on peut accéder à l'énergie libre de la surface, tout en discriminant les composantes
polaires ou apolaires de cette énergie en utilisant le modèle de Good Van Oss ou celui
de Owens Wendt.78 Ces modèles ne seront pas développés dans ce document car ils
sont liés à la détermination des tensions superficielles des liquides ou solides, ce qui
n’est pas lié à notre objectif dans ce projet.
30
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34
Chapitre 2: Crystallization control of
etherethersulfone copolymers by regular insertion
of an allyl functionality
Adrien Faye, Mikaël Leduc and Josée Brisson*, Polym. Chem., 2014, 5, 2548.
*Département de chimie and Centre de recherche sur les matériaux avancés
(CERMA),
Faculté des sciences et de génie, Université Laval,
1045 Avenue de la Médecine, Québec, Canada G1V 0A6.
E-mail: [email protected];
Fax: +1 418 656 7916;
Tel: +1 418 656 3536
35
Résumé
L’ADMET et la polycondensation par substitution nucléophile ont été utilisées pour
synthétiser des copolymères alternés à base de PEES. La polymérisation par ADMET
a conduit à des copolymères où un segment flexible (but-2-ène) est alterné avec des
blocs rigides étheréthersulfones (EES). Les copolymères obtenus sont de
configuration majoritairement trans avec plus de 94 à 98% de sélectivité, ont des Mw
qui atteignent 13 600 g mol-1 et sont de faibles polydispersités (Ip = 1,1 à 1,4).
D'autre part, la polycondensation a permis d'incorporer des segments flexibles de
configuration cis ou trans dépendamment du monomère utilisé. Des masses
moléculaires de même ordre grandeur ont été obtenues mais, comme prévu, avec des
Ip plus élevés (jusqu'à 2,3). La caractérisation des copolymères par DSC et par
diffraction des rayons X a permis de montrer que l'incorporation du segment de
configuration cis inhibe complètement la cristallisation, alors que l’isomère trans la
favorise. La cristallinité disparaît après la fusion, mais elle peut être restaurée en
recristallisant par un solvant approprié. La forme cristalline observée change avec la
longueur du bloc EES. Pour une unité de répétition de petite longueur (contenant un
bloc EES de 4 noyaux aromatiques), le segment flexible est incorporé dans l’unité de
répétition de la phase cristalline, tandis que, lorsque le bloc EES est porté à huit
noyaux aromatiques, le segment flexible est exclu de la phase cristalline. La
possibilité d’une post-fonctionnalisation du groupement flexible a été démontrée par
une réaction d’hydrogénation. Le copolymère résultant adopte une forme cristalline
différente pour le bloc de 4 noyaux aromatiques, mais, pour le bloc à 8 noyaux
aromatiques, la forme cristalline reste la même, confirmant ainsi que l'incorporation
du segment flexible dans l'unité de répétition cristallographique dépend de la
longueur du bloc.
36
Abstract
Acyclic diene metathesis (ADMET) polymerization and nucleophilic aromatic
substitution polycondensation are used to synthesize alternating copolymers based on
polyetherethersulfone (PEES) blocks. ADMET results in incorporation of trans-allyl
groups with more than 94 to 98% selectivity. The resulting polymers have a Mw of up
to 13 600 g mol-1 and low dispersity (Đ = 1.1 to 1.4). Polycondensation, on the other
hand, allows incorporation of either cis- or trans-allyl groups depending on the
starting monomers. Molecular weights in the same range are obtained, but with much
larger dispersity (up to 2.3), as expected. Characterization by differential scanning
calorimetry and wide angle X-ray diffraction shows that incorporation of the cis
group completely suppresses crystallization, whereas that of the trans group results in
semi-crystalline polymers. Crystallinity is lost post-melting, but can be restored using
appropriate solvent treatments. The crystal form changes with the length of the
etherethersulfone (EES) group indicating that, when the repeat unit is small
(containing a 4-ring etherethersulfone (EES) block), the allyl function is incorporated
into the crystallographic repeat, whereas when the EES segment increases to eight
rings, the allyl group is excluded from the crystal phase. Post-functionalization of the
allyl group is demonstrated by using hydrogenation. The resulting polymer adopts a
different crystal form for the 4-ring block, but the same crystal form for the 8-ring
block, confirming the dependence on the block length for incorporation into the
crystallographic repeat unit.
37
2.1 Introduction
Poly(ethersulfones) (PES) and poly(etherethersulfones) (PEES) show outstanding
thermal, chemical and radiative performances and are found in many applications.1
Modulation of properties such as hydrophobicity2, amphiphilicity3, glass transition
temperature4 or morphology via self-organization5 through random or block
copolymerization has been proposed to improve their properties and tailor these to
specific applications.
Little attention has been given to one specific morphological feature, which markedly
influences the resulting polymer properties: crystallinity. This is due to the fact that,
in spite of their regular structure, polyethersulfones are generally considered as being
amorphous. Although they are often slightly crystalline as synthesized, melting
during processing destroys this crystallinity, and annealing does not allow us to
restore it.
This is an unusual feature for such a regular homopolymer, partly attributed to an
abnormally narrow interval between Tg and Tm.6 However, long-term crystallization
occurs, and as the initially amorphous polymer slowly crystallizes, voids and cracks
may appear due to morphology reorganizations, thereby contributing to premature
failure.
Control of semi-rigid polymer crystallization through the introduction of regularly
inserted spacers has been the object of attention in our group. Previous work has
shown that introduction of flexible aliphatic chains of six to eight methylene units did
not decrease the crystallinity of poly(para-phenylene terephthalamides)7 (PPTA) and
poly(etheretherketones)8 (PEEK), and that single crystals could be obtained, the
flexible spacers being segregated at the crystal surface and acting as fold sites. A
crystallizable rigid block of one and a half repeat unit was found sufficient for the
resulting crystal structure to be the same as that of the parent rigid homopolymer in
PPTA-based copolymers7, in agreement with the previously proposed value of one
repeat unit9. Below this minimum requirement, the crystallographic repeat unit will
38
correspond to a combination of units forming a new homopolymer with a crystal
structure different from that of parent units.
In this work, two aims were sought: firstly, synthesis of PEES containing post-
functionalizable groups was targeted. These will allow fine-tuning of various
properties of the resulting polymers while minimizing synthetic efforts. Various
applications may in this way be targeted, but in the present work, only the proof of
concept will be made. Secondly, as a demonstration of the ability to modify polymer
properties through incorporation of an allyl spacer, modulation of the PEES ability to
crystallize was selected. The cis and trans isomers of the allyl group offer the
possibility of investigating whether the group promotes chain folding, either by pre-
orientation of chains in an antiparallel fashion or alternatively by favoring regular
alignment along the chain direction. In this respect, such a system can bring a
different light on the possible mechanism of polymer crystallization.
In the present work, two different synthesis approaches were used: acyclic diene
metathesis polymerization or ADMET for its low polydispersities and nucleophilic
aromatic substitution polycondensation, which allowed synthesis of cis- or trans-allyl
copolymers by changing the spacer inserted between rigid blocks. A rigid
ethersulfone block of four aromatic rings was first studied, and preliminary work on
eight-ring blocks will also be reported. In both cases, results are discussed in terms of
the ability of the allyl group to either inhibit or promote crystallization, the effect of
dispersity and the number of repeat units in the regular block. A few post-synthesis
modifications were made, to illustrate the concept of property changes through post-
functionalization.
39
2.2 Experimental section
2.2.1 Instrumentation
Nuclear magnetic resonance (NMR) spectroscopy measurements were performed in
CDCl3 or dimethyl sulfoxide-d6 solutions on a Bruker AMX 400 MHz at room
temperature.
Size exclusion chromatography (SEC) was carried out on a system composed of a
515 HPLC pump, two Agilent PL-Gel Mixed B-LS columns and a UV detector
Model 441 coupled to a LASER Dawn DSP photometer. Monodisperse poly(styrene)
standards were used for calibration and chloroform (CHCl3) as eluent at a flow rate of
1.0 mL min-1. The sample concentration was 0.175 mg mL-1. Chromatograms were
analyzed with the ASTRA software version 4.70.07.
Thermogravimetric analyses (TGA) were performed on a Mettler
TGA/SDTA851e/SF/1100 C equipped with an MT1 balance, under a nitrogen
atmosphere.
Glass transition Tg and melting temperatures Tm were determined as the midpoint of
the transitions using a differential scanning calorimeter (DSC) Mettler DSC823e
apparatus under a nitrogen atmosphere. The scan rate was 10 °C min-1 and liquid
nitrogen was used for cooling purposes. In some cases, cooling rates down to 1 °C
min-1 were used, and the selected samples were also annealed between Tg and Tm1 for
15 minutes to 24 hours. In all cases, the STARe software version 9.30 was used for
data acquisition and processing. The degree of crystallinity was estimated by DSC
using the following equation:
χDSC =∆𝐻𝑚
∆𝐻𝑚° x 100 (1)
40
where ∆𝐻𝑚 is the melt enthalpy, determined as the area under the melt endotherm,
and ∆𝐻𝑚° is the melt enthalpy of a completely crystalline sample. For the polymers
synthesized in this work, as the value of this constant was not known, as a first
approximation the value of 130 kJ g-1 for a polymer with a similar chemical structure,
poly(etheretherketone), was used.10
Crystallinity was studied by wide angle X-ray scattering (WAXS), using a Bruker
diffractometer equipped with a Kristalloflex 760 generator, a 3-circle goniometer and
a Hi-Star area detector. The generator produced graphite monochromatized copper
radiation (Cu Kα = 1.54178 Ǻ) at 40 kV and 40 mA. Diffraction diagrams were
recorded in the transmission mode. Crystallinity χx−ray was estimated from the
following equation:
χ𝑥−𝑟𝑎𝑦 =𝐼𝑐𝑟𝑦𝑠𝑡
𝐼𝑡𝑜𝑡𝑎𝑙 × 100 (2)
where Itotal is the total integrated intensity of the diffraction curve and Icryst is the
intensity of the crystalline peaks, determined by integrating the diffraction curve after
subtraction of the amorphous halo of a representative amorphous polymer.
Molecular models were built using HyperChem Pro 6.0 (Hypercube, Inc), energies
minimized using the block diagonal Newton–Raphson method until a root mean
square gradient of 0.1 kcal Ǻ-1 mol-1 was reached, and the force field used was MM+.
2.2.2 Materials
Bis(4-fluorophenyl) sulfone (99%), 4-methoxyphenol (99%), allyl iodide (98%),
boron tribromide (BBr3, 99.9%), N,N-dimethylacetamide (DMAc, 99+%), N-methyl
pyrrolidone (NMP), Grubbs 2nd generation catalyst (G2), Hoveyda–Grubbs catalyst
(HG) and palladium 10 wt% on activated carbon were all supplied by Sigma Aldrich
and used without any purification. Anhydrous acetone (C3H6O, 99.7%),
tetrahydrofuran (THF) and dimethylsulfoxide (DMSO) were purchased from Fisher
41
Scientific and used directly. Dichloromethane (CH2Cl2, Fisher Scientific, 99.9%) was
dried by stirring with CaH2 and then distilled prior to use. Anhydrous potassium
carbonate (K2CO3, 99%) was supplied by EMD.
2.2.3 Synthesis of monomers
2.2.3.1 Synthesis of 4,4’-bis(4-methoxyphenoxy) diphenyl sulfone (MPDS)
(Scheme 2.1a)
A round bottom flask (25 mL) was charged with 10.002 g (39.34 mmol) of bis(4-
fluorophenyl) sulfone, 9.767 g (78.68 mmol) of 4-methoxyphenol and 11.96 g (86.54
mmol) of potassium carbonate. To this mixture was added 40 mL of DMAc and the
resulting solution was stirred and heated to 180 °C over the course of 4 hours using
an oil bath, as shown in Scheme 2.1. The reaction mixture was allowed to cool and
precipitated into a 1 M HCl aqueous solution, filtered and washed with a saturated
NaCl aqueous solution three times to remove DMAc and potassium carbonate5. The
white solid was dried in vacuo at 60 °C for 8 hours (15.2 g, 32.8 mmol, 83%).
1H-NMR 400 MHz (CDCl3, r.t.) : δ 7.82 (d, 4H, 3J = 8.94 Hz, 4J = 2.50 Hz), 7.26
(CHCl3), 6.97 (d, 4H, 3J = 8.94 Hz, 4J = 2.50 Hz), 6.94 (d, 4H, 3J = 8.94 Hz, 4J =
2.50 Hz), 6.90 (d, 4H, 3J = 8.94 Hz, 4J = 2.50 Hz), 3.82 (s, 6H), 1.56 (H2O) ppm.
13C-NMR (CDCl3, r.t.) : δ 162.7, 156.8, 147.9, 134.9, 129.5, 121.7, 116.8, 115.1, 55.5
ppm.
42
a)
b)
Scheme 2.1: Synthesis of monomer precursors: (a) APDS (4-ring) precursor and (b)
HPSPPDS (8-ring) precursor
2.2.3.2 Synthesis of 4,4’-Bis(4-hydroxyphenoxy) diphenyl sulfone (HPDS)
(Scheme 2.1a)
As adapted from by Hayakawa et al.5, a round bottom flask (25 mL) containing a
magnetic stirrer was charged with 8.001 g (17.30 mmol) of 4,40-bis(4-
methoxyphenoxy) diphenyl sulfone (MPDS). To this mixture was added 20 mL of
dichloromethane, and the resulting solution was treated dropwise with 13.1 mL (138
mmol) of boron tribromide under completely dry conditions and under nitrogen. The
solution was stirred for 1 hour at 0 °C, an additional 5 hours at room temperature and
43
then poured into cold water (500 mL). The precipitate was filtered and recrystallized
from dichloromethane to purify it before being dried in vacuo at 60 °C for 8 hours
(7.513 g, 17.29 mmol, 99.96%).
1H-NMR 400 MHz ((CD3)2SO, r.t.): δ 9.52 (s, 2H), 7.84 (d, 4H, 3J = 8.94 Hz, 4J =
2.14 Hz), 6.99 (d, 4H, 3J = 8.94 Hz, 4J = 2.14 Hz), 6.94 (d, 4H, 3J = 8.94 Hz, 4J =
2.14 Hz), 6.80 (d, 4H, 3J = 8.94 Hz, 4J = 2.14 Hz), 5.76 (CH2Cl2), 3.34 (H2O), 2.50
(DMSO) ppm.
13C-NMR (CDCl3, r.t.): δ 163.0, 155.2, 146.4, 134.9, 130.1, 122.3, 117.1, 116.9 ppm.
2.2.3.3 Synthesis of 4,4’-bis(4-allyloxyphenoxy) diphenyl sulfone (APDS)
(Scheme 2.1a)
Anhydrous K2CO3 was added to a solution of 4,4’-bis(4-hydroxyphenoxy) diphenyl
sulfone (HPDS) (4.518 g, 10.40 mmol) and 18-crown-6 (0.566 g, 2.142 mmol) in
acetone (20 mL). The reaction mixture was stirred at room temperature for 2 hours
under a nitrogen atmosphere, treated with allyl iodide (2.0 mL, 21 mmol) and heated
at 60 °C for 6 hours using an oil bath. The reaction mixture was cooled to room
temperature, quenched with aqueous NaCl, and concentrated under reduced pressure.
The crude product was diluted with dichloromethane and extracted with H2O. The
organic layer was dried over MgSO4 and filtered, and the solvent was evaporated.
The white solid was filtered and dried in vacuo at 60 °C for 8 hours (2.9 g, 5.6 mmol,
54%).
1H-NMR 400 MHz (CDCl3, r.t.): δ 7.82 (dd, 4H, J = 9.02 Hz, J = 2.00 Hz), 7.26
(CHCl3), 6.96 (dd, 4H, 3J = 9.27 Hz, 4J = 2.50 Hz), 6.94 (dd, 4H, 3J = 9.02 Hz, 4J =
2.00 Hz), 6.91 (dd, 4H, 3J = 9.27 Hz, 4J = 2.50 Hz), 6.01 (m, 2H, 3Jtrans = 17.28 Hz,
3Jcis = 10.51 Hz, 3J = 5.30 Hz), 5.40 (ddd, 2H, 3Jtrans = 17.28 Hz, 4J = 3.15 Hz, 2J =
1.60 Hz), 5.29 (ddd, 2H, 3Jcis = 10.51 Hz, 4J = 2.82 Hz, 2J = 1.39 Hz), 4.53 (dt, 4H, 3J
= 5.30 Hz, 4J = 3.05 Hz, 4J = 1.55 Hz), 1.56 (H2O) ppm.
44
13C-NMR (CDCl3, r.t.): δ 162.7, 155.9, 148.1, 135.0, 133.0, 129.6, 121.7, 117.9,
116.9, 116.0, 69.2 ppm.
2.2.3.4 Synthesis of 4-fluoro-4’-hydroxy diphenyl sulfone (FHDS) (Scheme 2.1b)
A round bottom flask (25 mL) containing a magnetic stirrer was charged with 15.001
g (59.000 mmol) of bis(4-fluorophenyl sulfone) (FPS) and 2 eq. of aqueous KOH 7.0
M (16.9 mL, 118 mmol). To this mixture was added 20 mL of DMSO and the
resulting solution was heated to 75 °C for 20 hours using an oil bath, as shown in
Scheme 1b. The reaction mixture was allowed to cool, poured dropwise into 50 mL
of water and washed 3 times with 100 mL of toluene. The aqueous phase was
recovered and then acidified with 100 mL of HCl 8M. The solution was stirred for 5
minutes and then filtered. The white product obtained (13.1 g, 51.9 mmol, 88%) was
dried at 60 °C under vacuum for 8 hours.
1H-NMR 400 MHz ((CD3)2SO, r.t.): δ 10.65 (s, 1H), 7.93 (d, 1H, 3J = 8.85 Hz, 4J ¼
2.04 Hz), 7.75 (d, 1H, 3J = 8.85 Hz, 4J = 2.04 Hz), 7.40 (d, 1H, 3J = 8.85 Hz, 4J =
2.04 Hz), 6.90 (d, 1H, 3J = 8.85 Hz, 4J = 2.04 Hz), 3.33 (H2O), 2.50 (DMSO) ppm.
13C-NMR 400 MHz ((CD3)2SO, r.t.): δ 165.6, 163.1, 138.5, 130.4, 129.9, 129.8,
129.7, 129.2, 116.0 ppm.
2.2.3.5 Synthesis of 4-fluoro-4’-methoxy diphenyl sulfone (FMDS) (Scheme 2.1b)
A round bottom flask (25 mL) containing a magnetic stirrer was charged with 3.279 g
(13.00 mmol) of 4-fluoro-40-hydroxy diphenyl sulfone (FHDS), 1.845 g (13.00
mmol) of iodomethane and 2.156 g (15.60 mmol) of potassium carbonate. To this
mixture was added 20 mL of DMAc and the resulting solution was heated to 75 °C
for 20 hours using an oil bath (Scheme 1b). The reaction mixture was allowed to cool
and precipitated dropwise into 150 mL of aqueous KOH 1 M. The solution was
stirred for 5 minutes and then filtered. The white product obtained was dissolved in
dichloromethane and filtered, and the solvent was evaporated under reduced pressure.
45
The product was dried at 60 °C under vacuum for 8 hours (3.400 g, 12.77 mmol,
98%).
1H-NMR 400 MHz (CDCl3, r.t.): δ 7.90 (d, 1H, 3J = 8.89 Hz, 4J = 2.13 Hz), 7.84 (d,
1H, 3J = 8.89 Hz, 4J = 2.13 Hz), 7.26 (CHCl3), 7.12 (d, 1H, 3J = 8.89 Hz, 4J = 2.13
Hz), 6.95 (d, 1H, 3J = 8.89 Hz, 4J = 2.13 Hz), 3.83 (s, 3H), 1.56 (H2O) ppm.
13C-NMR 400 MHz (CDCl3, r.t.): δ 166.3, 163.8, 138.3, 132.8, 129.9, 129.7, 116.4,
116.2, 114.5, 55.58 ppm.
2.2.3.6 Synthesis of 4,4’-bis(4-(4-(4-methoxyphenylsulfonyl)
phenoxy)pentoxy)diphenylsulfone (MPSPPDS) (Scheme 2.1b)
A round bottom flask (25 mL) containing a magnetic stirrer was charged with 0.800 g
(1.84 mmol) of 4,4’-bis(4-hydroxyphenoxy) diphenyl sulfone (MPDS), 0.980 g (3.68
mmol) of 4-fluoro-4’-methoxy diphenyl sulfone (FMDS) and 0.560 g (4.05 mmol) of
potassium carbonate. To this mixture was added 30 mL of DMAc and the resulting
solution was heated to 180 °C over the course of 20 hours using an oil bath. The
reaction mixture was allowed to cool and precipitated into a 1 M aqueous HCl
solution, filtered and washed with a saturated NaCl aqueous solution three times to
remove DMAc and potassium carbonate. The white solid was dried in vacuo at 60 °C
for 8 hours (1.62 g, 1.75 mmol, 95%).
1H-NMR 400 MHz (CDCl3, r.t.): δ 7.87 (d, 4H, 3J = 8.80 Hz), 7.85 (d, 4H, 3J = 8.80
Hz), 7.26 (CHCl3), 7.05 (s, 8H), 7.01 (d, 4H, 3J = 8.80 Hz), 7.00 (d, 4H, 3J = 8.80
Hz), 6.95 (d, 4H, 3J = 8.80 Hz), 3.84 (s, 6H) ppm.
13C-NMR 400 MHz (CDCl3, r.t.): δ 163.2, 161.7, 161.4, 151.8, 151.6, 136.2, 135.6,
133.3, 129.7, 129.6, 121.9, 121.8, 117.5, 114.4, 55.58 ppm.
46
2.2.3.7 Synthesis of 4,4’-bis(4-(4-(4-hydroxyphenylsulfonyl)phenoxy)phenoxy)
diphenyl sulfone (HPSPPDS) (Scheme 2.1b)
A round bottom flask (25 mL) containing a magnetic stirrer was charged with 2.966 g
(3.200 mmol) of 4,4’-bis(4-(4-(4-methoxyphenylsulfonyl)phenoxy)phenoxy)
diphenyl sulfone (MPSPPDS). To this mixture was added 20 mL of dichloromethane
and the resulting solution was treated dropwise with 3.9 mL (42 mmol) of boron
tribromide under the same conditions (synthesis and subsequent workup) as described
for HPDS (2.25 g, 2.50 mmol, 78%).
1H-NMR 400 MHz ((CD3)2SO, r.t.): δ 10.6 (s, 2H), 7.91 (d, 4H, 3J = 8.89 Hz), 7.86
(d, 4H, 3J = 8.89 Hz), 7.73 (d, 4H, 3J = 8.89 Hz), 7.20 (s, 8H), 7.12 (d, 4H, 3J = 8.89
Hz), 7.10 (d, 4H, 3J = 8.89 Hz), 6.89 (d, 4H, 3J = 8.89 Hz), 3.33 (H2O), 2.50 (DMSO)
ppm; 13C-NMR 400 MHz ((CD3)2SO, r.t.): δ 161.9, 161.5, 161.1, 151.4, 151.2, 136.1,
135.2, 131.1, 129.8, 129.7, 129.5, 122.3, 122.2, 117.7, 116.1 ppm.
2.2.4 Copolymer synthesis
2.2.4.1 ADMET polymerization of poly(allyl-co-etherethersulfone) (PA-4EES)
(Scheme 2.2a)
The APDS monomer (0.500 g, 0.971 mmol) was dissolved in dichloromethane in a
two-neck flask. The catalyst (G2 or HG, 1- 6.0 mol %) was then added and the
reaction mixture was stirred and heated at 40 °C using an oil bath under a continuous,
low nitrogen flow for one day. Subsequently, ethyl vinyl ether (0.4 mL) was added to
quench the reaction. The obtained product was dissolved in dichloromethane and
precipitated by slowly dropping the solution into cold methanol, filtering off the
solvent and washing the powder with acetone. To remove ruthenium, the polymer
was dissolved again in dichloromethane and then washed three times with 100 mL of
a 0.224 M aqueous solution of sodium diethyldithiocarbamate trihydrate. The product
was finally dried in vacuo at 60 °C overnight. The resulting polymers are designated
47
PA-4EES, where A stands for the allyl group polymerized during the ADMET
reaction, and 4 corresponds to the number of rings in the rigid ethersulfone monomer.
2.2.4.2 Polycondensation of PTA-4EES, PTCA-4EES, PTA-8EES and PCA-
8EES copolymers (Schemes 2.2b and 2.2c)
A round bottom flask (25 mL) containing a magnetic stirrer was charged with 1.216 g
(8.800 mmol) of anhydrous K2CO3, 1.738 g (4.000 mmol) of the 4-ring monomer
HPDS or 3.596 g (4.000 mmol) of the 8-ring monomer HPSPPDS and 0.500 g (4.000
mmol) of either (Z)-1,4-dichlorobut-2-ene (Z-DCB) or (E)-1,4-dichlorobut-2-ene (E-
DCB). To this mixture was added 10 mL of DMAc and the resulting solution was
heated between 70 °C and 120 °C for one to two days using an oil bath. The reaction
mixture was allowed to cool and precipitated into a 1 M HCl aqueous solution. The
polymer was filtered and dried, redissolved in DMAc, and again precipitated to
ensure salt removal. The resulting polymers are abbreviated PTA-xEES for the E-
DCB synthesis with an x-ring monomer and PCA-xEES for the Z-DCB synthesis.
2.2.4.3 Polycondensation of the PAE-4EES copolymer (Scheme 2.2d)
A round bottom flask (25 mL) containing a magnetic stirrer was charged with 0.869 g
(2.000 mmol) of 4,4’-bis(4-hydroxyphenoxy) diphenyl sulfone (MPDS), 0.030 g
(0.093 mmol) of tetrabutylammonium bromide (TBAB) and 6mL of NaOH 1 M. The
mixture was stirred until everything was dissolved. To this solution was added 0.306
g (2.000 mmol) of fumaryl chloride, and the mixture was stirred rigorously at room
temperature for 4 hours. The supernatant aqueous layer was decanted and the mixture
was then poured into hot water (200 mL) containing a few drops of concentrated
hydrochloric acid. The crude product (0.850 g, 98%) was collected by filtration,
washed with refluxing methanol, and dried at 80 °C under vacuum overnight.
2.2.4.4 Hydrogenation to obtain PAH-4EES and PAH-8EES
In a solution of PTA-xEES (0.240 g) in dichloromethane (20 mL) was added 10 wt%
palladium on activated carbon (0.080 g) while stirring at ambient temperature. The
48
mixture was purged with hydrogen to replace the air in the flask and then stirred
under a hydrogen atmosphere for 3 hours. The palladium activated carbon was
filtered off, and the solvent was removed under reduced pressure to give the
hydrogenated polymer with a 99% yield. The resulting polymers are abbreviated
PAH-xEES, where H stands for the hydrogenation of the allyl group. The same
abbreviation is used for polymers prepared by using the ADMET monomers, the cis-
containing or the trans-containing monomers, as these will yield the same polymer,
the only difference being the average molecular weights and polydispersities, which
remain, within experimental error, the same as the starting polymer.
2.2.4.5 Halogenation to obtain PACl-4EES and PABr-4EES
A round bottom flask (25 mL) containing a magnetic stirrer was charged with 0.375 g
of PCA-4EES in dichloromethane (20 mL). The mixture was purged with argon and
then stirred under a chlorine atmosphere for 3 hours. The solvent was removed under
reduced pressure to give the chlorinated polymer with a 99% yield. The resulting
polymer is abbreviated PACl-4EES, where Cl stands for the chlorine of the allyl
group. A round bottom flask (25 mL) containing a magnetic stirrer was charged with
0.600 g of PCA-4EES in dichloromethane (15 mL). To this solution was added
dropwise, under vigorous stirring, bromine (0.036 mL, 0.815 mmol) in 2 mL of
CH2Cl2, as adapted from ref. 11. The mixture was allowed to react for 2 hours and
then poured into water. The precipitated product was filtered and washed with ether.
The brominated polymer, PABr-4EES, was obtained with a yield of 99.5%.
2.2.5 Recrystallization of copolymers.
Solvent recrystallisation was performed by dissolving 5 mg of a polymer in 5 mL of a
solvent or solvent mixture, and the solution was poured into a small Petri dish and
covered. For low boiling-point solvents (THF, CH2Cl2), samples were placed at 4 °C
until evaporation occurred. For samples with higher boiling points, evaporation was
performed at room temperature.
49
2.2.6 Results and discussion
2.2.6.1 Synthesis of polymers
a)
c)
b)
d)
Scheme 2.2: Polymerization reactions: (a) acyclic diene metathesis polymerization
(ADMET) of the APDS monomer, (b) polycondensation of HPDS with (Z) and (E)-1,4-
dichlorobut-2-ene, (c) polycondensation of HPSPPDS with (Z) and (E)-1,4-dichlorobut-2-
ene and (d) polycondensation with fumaryl chloride to insert ester linkages.
50
2.2.6.1.1 PA-4EES copolymer obtained by ADMET polymerization
ADMET was used to polymerize a diallyl-terminated 4-ring macromonomer
obtained, as depicted in Schemes 2.1 and 2.2. The 4-ring block corresponds to an
etherethersulfoneether moiety, or EESE, but by analogy with the 8-ring monomer, it
was chosen to use the EES abbreviation for this polymer, this being the sequence
common to both copolymers. The resulting copolymers are film-forming, but film
brittleness was an indicator of low molecular weight. This was confirmed by NMR
spectroscopy and SEC, as reported in Table 2.1. SEC determination of molecular
weight is relatively straightforward, although the use of poly(styrene) standards can
induce a systematic error on molecular weights. NMR was therefore also used to
quantify molecular weights. Representative NMR spectra are presented in Figure 2.1.
Three small-intensity signals appearing between 4.0 and 6.3 ppm are related to
terminal allyl groups, and decrease in intensity until they disappear into the
background noise with increasing molecular weight. To better visualize the
attribution of these small-intensity peaks, in Figure 2.1b is reported a close-up view
of this spectral region, along with that of an allylated monomer. Protons appearing at
the chain end are denoted by ‘EG’ for the end-group, whether these appear as the
polymer end-group or at the terminal position of the monomer. Peak fEG is a multiplet
in the monomer and the copolymer, whereas peak f is a singlet next to this multiplet.
A very small intensity peak is also observable for the f protons of the cis fraction of
the trans copolymer. Likewise, the e region presents a doublet for the end-groups and
a singlet for hydrogen atoms in the main chain, and a small ‘cis’ peak is also
observed. Spectra were used to calculate number-average molecular weights Mn, as
reported in Table 2.1 (see Scheme A.2.1 for details on Mn calculation), along with
values obtained by SEC. As shown by SEC and as expected, ADMET polymers have
low dispersity.
Molecular weights of 2000 g mol-1 were first obtained. In order to increase the
molecular weight, the amount and the nature of the catalyst, reaction temperature and
reaction time were varied12, but the highest molecular weight achieved was a
51
relatively low value of Mw of 8700 g mol-1 for 6% catalyst at 40 °C for 24 hours
using the Hoveyda–Grubbs catalyst. It is proposed in the literature that molecular
weight can be limited, for this type of polymer due to a coordination bond occurring
between the active center of the catalyst, i.e. ruthenium, and the sulfone group13 or
the ether oxygen during the formation of a metallacyclobutane intermediate,14 thus
disabling the catalyst. This phenomenon has been termed the “negative neighboring
group effect”.15 Tindall et al.14 proposed that the optimum conditions for ADMET
chemistry occur by positioning the functional group at least two methylene units
distant from the metathesizing olefin within the monomer unit. To add a methylene
group between the allyl double bond and the ether oxygen was considered, but as this
would probably decrease the glass transition temperature and degradation temperature
of the resulting polymer, this was not pursued.
Polycondensation yielded slightly higher molecular weights with the cis-monomer,
which were found to be optimal for a reaction temperature of 120 °C, as reported in
Table 2.1. For a reaction temperature up to 150 °C, the molecular weight was
relatively low and no conversion of cis to trans allyl or trans to cis could be detected.
The use of higher temperatures resulted in higher molecular weights especially of the
cis-allyl copolymers. Nevertheless, the low reactivity of the hydroxyl group and high
number of termination reactions limited the obtained molar weight.
A second factor that may have contributed to obtaining low molecular weights is
crystallinity. Crystalline polymers tend to be less soluble than their amorphous
counterparts, and as the polymer crystallizes during polymerization, precipitation can
occur, and chain growth then stops, which leads to low molecular weights16. This
would also explain why temperature has a much more marked effect for the cis-allyl
copolymers than for the more crystalline trans-allyl copolymers.
In order to further improve molecular weights, an additional reaction was performed
using an acid chloride terminated allyl spacer instead of a chloride terminated spacer
in order to replace the ether linkage between the EES block and the allyl spacer by an
ester linkage, as shown in Scheme 2.2d. Due to the higher reactivity of this group,
52
reactions could be performed at room temperature, and higher molecular weights
were achieved, as reported in Table 2.1. This polymer is a better candidate for
eventual applications, but exhibits a lower solubility and a much higher
polydispersity, thus making the ether-linked copolymers more interesting subjects for
fundamental studies on crystallization.
2.2.6.1.2 PTA-xEES and PCA-xEES polymers obtained by polycondensation
To know whether the polymer synthesized by ADMET was in a cis or trans
configuration, FTIR spectroscopy is normally used. In the present case, overlap of
ethersulfone vibration bands made such an attribution less straightforward. Therefore,
it was decided to rely on NMR peak positions of allyl protons to determine this
configuration. To have representative NMR spectra with which comparisons could be
made, polycondensation reactions were performed to synthesize copolymers having
the same chemical structure but with either cis or trans-allyl bonds, as shown in
Scheme 2.2b. This approach further has the advantage of yielding the desired allyl
conformation by choosing the right monomer, but does increase the resulting
dispersity. Molecular weights and polydispersities of these copolymers were
determined by SEC and reported in Table 2.1. The obtained copolymers are in the
same range of molecular weights as those obtained by ADMET, but have much larger
Đ values, as expected.
NMR peak positions for the cis- and trans-allyl isomers are different, allowing easy
determination of isomers present, as reported in Table 2.2. In the trans copolymer
spectrum, a small peak, which represents 10% of the total signal, is present at the
position of the cis isomer. This cis isomer is due to the presence of 10% cis form in
the initial E-DCB monomer (see Figure A.2.4b of the Annexes), purification of the
trans isomer being extremely difficult. This small portion therefore remains in the
polymer.
Comparison of peak positions of PTA-4EES, PCA-4EES and PA-4EES polymers is
reported in Table 2.2, and shows a match between the ADMET polymer, abbreviated
53
PA-4EES, and the trans isomer (PTA-4EES). Inspection of the NMR spectra in
Figure 2.1 shows that, in the ADMET polymer, from 1 to 6% of the cis form is
present, which is less than that in the polycondensation polymer, for which up to 10%
cis isomer was present due to their presence in the starting monomer. A very high
stereoselectivity is therefore achieved with both the Grubbs 2nd generation and the
Hoveyda–Grubbs catalysts for this polymer, along with a low dispersity, and with
molecular weights comparable to those of step-growth polycondensation, although
modest.
Polymers were synthesized using two ethersulfone blocks: the 4-ring block in
polymers abbreviated PTA-4EES and PCA-4EES but which, as mentioned above,
have a EESE block, and the 8-ring block in PTA-8EES and PCA-8EES, which have a
ESEESEES block.
54
a)
b)
Figure 2.1: 1H-NMR spectrum of the representative monomer and polymers obtained by
ADMET: (a) PA-4EES, Mn = 2200 g mol-1 and (b) enlargement showing end-groups for
PA-4EES with two different molecular weights and for the monomer.
55
2.2.7 Post-polymerization reactions
Hydrogenation of the allyl double bond allowed us to obtain PAH-4EES and PAH-
8EES copolymers with more than 99% yield, thus demonstrating that the double bond
remains highly accessible for future reactions, as expected. All copolymers
synthesized were hydrogenated post-reaction. A total absence of peaks related to the
allylic function is noted in NMR spectroscopy (see Figure A.2.10c of the Annexes).
Removing the double bond results in the presence of a tetramethylene aliphatic
spacer. This imparts additional flexibility to the polymer, but may not be sufficient to
favor crystallization via chain folding, since even when taking into account adjacent
ether groups, this chain length is small as compared to the minimum five to eight
bond requirement estimated for most polymers.17–20
However, changing this segment will allow us to verify whether the allylic group is
incorporated into the crystallographic unit, as changing from an allylic group to an
aliphatic chain should provide enough structural variation to induce changes in unit
cell dimensions, conformation and packing, and should therefore result in observable
changes in the X-ray diffraction diagram, as will be discussed later.
To further illustrate the possible modifications of allyl group, chlorination and
bromination reactions were performed on PCA-4EES. These reactions were chosen
for their high yields, and hydrogen atom groups were replaced by chlorine or bromine
atoms in a 99% yield in both cases, as determined by proton NMR spectroscopy (see
Figures A.2.10d and A.2.10e of the Annexes).
56
Table 2.1: Molecular weights and dispersity of polymers synthesized by ADMET
and polycondensationa
Polymers
Reaction conditions
Mn
(NMR)
g mol-1
Mn
(SEC)
g mol-1
Mw
(SEC)
g mol-1
Ip
PA-4EES G2, 1 mol% CH2Cl2, 24 hr, 40 °C 2000 3300 3600 1.1
PA-4EES G2, 6 mol% CH2Cl2, 24 hr, 40 °C - 4900 6400 1.3
PA-4EES HG, 1 mol% CH2Cl2, 24 hr, 40 °C 2200 3600 4000 1.1
PA-4EES HG, 6 mol% CH2Cl2, 24 hr, 40 °C - 6200 8700 1.4
PTA-4EES DMAc, 24 hr,70 °C - 2600 4600 1.8
PTA-4EES DMAc, 48 h, 90 °C - 4100 5700 1.4
PTA-4EES DMAc, 48 h, 120 °C - 900 1500 1.7
PTA-4EES DMAc, 48 h, 150 °C - 900 1200 1.3
PCA-4EES DMAc, 24 hr,70 °C - 4900 8500 1.7
PCA-4EES DMAc, 48 hr,90 °C - 4700 7400 1.6
PCA-4EES DMAc, 48 hr,120 °C - 8400 13 600 1.6
PCA-4EES DMAc, 48 hr,150 °C - 1200 1900 1.6
PTA-8EES DMAc, 24 hr,70 °C - 1700 1900 1.1
PCA-8EES DMAc, 24 hr,70 °C - 1800 4100 2,3
PAE-4EES CH2Cl2, 4 h, 20 °C - 7700 38 000 4.9
aG2: Grubbs second generation catalyst, HG: Hoveyda–Grubbs catalyst.
57
Table 2.2: Proton chemical shifts (d) of the allyl group in cis- and trans
poly(etherethersulfones) obtained by polycondensation and by ADMET (major
configuration trans)
Polymers δ (e) (ppm) δ (f) (ppm)
PA-4EES 4.58 6.10
PTA-4EES 4.58 6.09
PCA-4EES 4.66 5.94
2.2.8 Thermal properties of the copolymers
2.2.8.1 Thermogravimetric analysis (TGA)
Polymers obtained by ADMET and by step-growth polycondensation were
characterized by thermogravimetric analysis (TGA) to investigate their thermal
resistance, one of the assets of PES and PEES. As shown in Figure 2.2, degradation
starts around 370 °C, with a slightly better thermal resistance for the cis polymers.
For the 8-ring polymer, a second degradation step occurs around 550 °C, slightly
above the poly(ethersulfone) homopolymer degradation temperature, which is around
400 °C.21 A decrease in degradation onset temperature as compared to PES was
expected due to the addition of the flexible, aliphatic containing allyl moiety in the
polymer chain.21 This loss in thermal stability is however in part counterbalanced by
the possibility of post-functionalizing the allyl group.
58
Figure 2.2: Thermal stability of representative 4-ring and 8-ring polymers as
determined by thermogravimetry.
2.2.8.2 Differential scanning calorimetry (DSC)
As one of the aims of this work was to tune crystallinity by incorporating a spacer
along the PEES chain, differential scanning calorimetry becomes a method of choice
to investigate these polymers. As mentioned in the Introduction, the temperature
difference between Tg and Tm has been proposed to be one of the main factors
inhibiting crystallization of poly(ethersulfones). DSC can further determine the effect
of thermal history on crystallinity.
Several heating and cooling scans were performed, at a constant speed of 10 °C min-1.
Heating, cooling and reheating scans of one of the polymers, PA-4EES, are reported
in Figure 2.3a. During the first heating scan, two endotherm peaks appear,
corresponding to a double melting behaviour, consistent with the presence of a
crystalline phase. It was difficult to detect the glass transition during this first scan,
indicating a high crystallinity. During the cooling scan, a glass transition is clearly
observed, but no crystallization peak is observed. In the second heating scan, the
59
glass transition still appears, and no melting peaks are observed. This is in agreement
with the reported behaviour of poly(ethersulfones), which do not crystallize readily
after melting.
a)
b)
Figure 2.3: Differential scanning calorimetry: (a) heating and cooling scans for PA-
4EES and (b) first heating scan for representative polymers
60
Figure 2.3b reports the first heating scan of polymers synthesized in this work. The
same general behaviour was observed for all trans-containing polymers (PA-4EES,
PTA-4EES, PTA-8EES), in the presence of a single or double melting peak in the
first scan and only a glass transition in subsequent scans, to which is often
superimposed a relaxation peak. NMR analysis of the PTA-4EES copolymer post-
melting shows that the allyl group is still in its trans form, thus eliminating the
possibility that the incapacity to recrystallize after melting is related to heat induced
isomerization of the allyl group. (NMR spectra are reported Figure A.2.11). In some
cases, a peak may be observed, but as on the second scan, this is replaced at the same
position by a glass transition, it is interpreted as a relaxation peak superimposed to
the glass transition and not as a melt endotherm (PAH-4EES and PCA-4EES). Only
PA-4EES shows a double endothermic peak, which will be discussed separately.
In order to induce crystallization for initially amorphous polymers, or to restore them
after melting for initially crystalline polymers, various annealing treatments between
Tg and Tm (at temperatures varying from 110 to 125 °C) were performed for up to 24
hours. Cooling down to 1° min-1 was also tested from the melt. In all cases, polymers
remained completely amorphous, in keeping with the usual PES and PEES thermal
behaviour. This clearly indicates that the incorporation of an allyl group does not
increase crystallization speed enough to allow annealing-induced crystallization.
The exact position of the glass transition and melt endotherms are reported in Table
2.3. The glass transition temperature varies slightly with the content of cis isomer (Tg
decreases from PC4-EES to PTA-4EES to PA-EES, which contains the least
percentage of cis groups), which is attributed to a higher steric hindrance in the cis
isomer. PTA-8EES stands out as being the lowest molecular weight polymer
synthesized, which explains the observed Tg lower by approximately 20 °C. Upon
hydrogenation of the allyl group, the glass transition endotherms shift to a lower
temperature, in agreement with a higher chain mobility. Upon chlorination and
bromination of the allyl group, hindered mobility due to the size of the substituents
results in a return of the Tg to the value observed for the allyl copolymer. In other
61
synthesized copolymers, no notable effect of molecular weight was observed on
either Tg or melting point. In the 4EES series, the highest Tg was observed for the
ester-linked PAE-4EES. The value is higher by 5 to 10 degrees only, and this increase
could be attributed to the combined effects of chain rigidification by the ester linkage
and to the higher molecular weight of this copolymer. Tg also varies with relative
proportion of EES, this segment being more rigid than the ally spacer. The observed
glass transition temperatures are smaller by approximately 70° to 100 °C than those
of PES (for which values of 205 (ref. 22) to 230 °C (ref. 23) have been reported) or of
PEES (210 °C value reported by Kitipichai et al.).24
The melting points of the synthesized copolymers are also notably different from that
of PEES for which Johnson et al. indicate a value of 310 °C for PEES.21 The highest
value obtained in this work was 179 °C for ester-linked PAE-4EES, again attributed
to the higher chain rigidity and molecular weight of this polymer. For the ether linked
copolymers, the highest melting point observed is the second melting point of PA-
4EES. More importantly, the difference between Tg and Tm remains well below the
usual 100 degrees value observed for most polymers, with values of 32 to 36 °C for
the 4-ring ether-linked block copolymers, 57 °C for the ester-linked 4-ring copolymer
and 72 °C for the ether-linked 8-ring block copolymer. It is therefore a lower
temperature difference than that of PES, which is between 80 to 100 °C, in agreement
with their inability to crystallize upon annealing. Therefore, this factor can be
invoked to explain the lack of crystallization upon annealing, although other factors
must be at play to explain the observed differences from one polymer to another as
synthesized.
Unfortunately, since little is known about the crystal structure of PES or PEES, no
melt enthalpy of the pure crystal form has been reported. It is therefore not possible to
determine accurate crystallinity using DSC-measured melt enthalpy. Nevertheless, if
supposing a value equal to that of poly-(etheretherketone), which are chemically
similar but for which the crystal structure is different,25 crystallinity was estimated
62
and is reported in Table 2.3. Values obtained vary between 0 to 28% for the polymers
as synthesized.
Table 2.3 : Thermal properties and degree of crystallinity χ of copolymers
Mw x 103
g/mol
Tg
°C
Tm1
°C
Tm2
°C
∆Hm
J/g χDSC
%
χX-ray (%)
In.a Rec.a
PA-4EES 6.8 98 133 159 39.5 30 25 37
PA-4EES 8.7 94 130 152 36.2 28 25 37
PTA-4EES 4.1 108 140 - 28.2 22 23 28
PCA-4EES 7.5 115 - - - 0 0 0
PAH-4EES 7.5 105 137 - 10.1 8 18 25
PCA-8EES 4.1 136 - - - 0 0 0
PTA-8EES 1.9 84 156 - 36.0 28 37 42
PAH-8EES 4.1 115 - - - 0 0 50
a In. : Initial, as synthesized Rec.: Recrystallized in a mixture of CH2Cl2 and benzylic alcohol.
2.2.9 X-ray diffraction
X-ray diffraction was performed to investigate the crystallinity of the synthesized
copolymers and to compare their crystalline form. In order to have accurate
information on the peak position, and to eliminate changes associated with the use of
different solvents or temperatures, samples were recrystallized. Annealing was not
useful in this case, as demonstrated by DSC experiments. Only one method has been
published for recrystallizing PES polymers, by slow evaporation of methylene
chloride solutions at low temperatures.26 In the present work, various solvent systems
were tested for PA-4EES. For CH2Cl2 and THF, crystallization was conducted at cold
temperature in order to obtain slow evaporation, following the work of Blackadder et
al.26 For solvents which naturally evaporate slowly, this was not found necessary. X-
ray diffraction diagrams of samples which yielded high crystallinities are reported in
Figure 2.4.
63
Whereas for the PA-4EES copolymer only a slight crystallinity was observed in
CH2Cl2, marked crystallinity could be obtained by using THF, DMAc or NMP.
Polymorphism may be present, as the diffraction diagrams obtained in NMP present
an additional medium-intensity reflection near 47 °C. The best crystallinity was
obtained for a mixture of methylene chloride containing 10% benzyl alcohol with 7
reflections clearly observed in the 20 to 30 °C range, and several lower intensity
reflections observable at higher angles. This solvent system was subsequently used
for all polymers synthesized in this work.
Figure 2.4: X-ray diffraction diagrams of PA-4EES as recrystallized by evaporation
from various solvents
In Figure 2.5a are reported the X-ray diffraction diagrams of the as-synthesized
polymers, along with that of a low molecular weight PES (Mw = 1600 g mol-1, Đ =
1.15) previously synthesized in our group.25 The PES homopolymer is amorphous,
but has a relatively narrow peak width, which may indicate partial organization in the
amorphous phase. Diagrams corresponding to completely amorphous polymers with
64
larger peak width are obtained for the cis-allyl polymers, PCA-4EES and PCA-8EES
as well as one of the two hydrogenated polymers, PAH-8EES.
a) b)
Figure 2.5: X-ray diffraction diagrams of EES-containing copolymers: (a) as
synthesized and (b) after recrystallization by evaporation from dichloromethane–
benzyl alcohol solutions
All other polymers show a superposition of discrete diffraction peaks over the
amorphous halo. Trans-allyl polycondensation PTA-4EES and ADMET PA-4EES
copolymers share the same diffraction peak positions, and similar relative intensities
of the diffraction peaks as compared to the amorphous halo, indicating similar
crystallinities and confirming the DSC results. This similarity also confirms the NMR
results showing that PA-4EES comprises almost exclusively trans-allyl groups.
Crystallinity can be sensitive to the solvent used, which is not the same in both
synthesis methods, but no marked effects were found in this case. Upon
hydrogenation (PAH-4EES), the diffraction diagram changes in terms of peak
65
positions and relative intensities, indicating that a new crystalline form is observed.
This new form is closer to that of PTA-8EES, as the most intense peaks are at the
same position and relative intensities are similar, which may indicate that a similar
conformation and packing is adopted. Upon chlorination, no discrete diffraction
peaks appear, but the ‘amorphous’ peak is very narrow, much narrower than that of
PES, a sign that a mesophase with partial pre-ordering is probably present. Upon
bromination, on the other hand, a few discrete diffraction peaks are observed, but the
crystallinity as-synthesized is low, in agreement with DSC results. Various factors are
most probably at play and affect crystallization, which may include rigidity, steric
hindrance, and electrostatic interactions, and which affect crystallization in an
unpredictable way, the bulkier group (Br) not resulting in the lowest crystallinity.
Finally, the 8-ring hydrogenated polymer is completely amorphous as synthesized.
From these observations, a tendency emerges: cis groups incorporation along the
main chain suppress crystallization of the as-synthesized polymer, whereas trans-
groups promote it. Changes in the dispersity do not affect crystallinity as observed by
X-ray diffraction, as demonstrated by the comparison of PA-4EES and PTA-4EES
diffraction diagrams.
Once the polymers are recrystallized in a slowly evaporating solvent, higher
crystallinities are obtained, and these allow better measurements of peak position and
relative intensities, which are reported in Table A.2.1 of the Annexes. Only two
polymers remain amorphous, the two cis-containing polymers, as seen in Figure 2.5b,
which indicates that the cis group is more effective at suppressing crystallinity than
the 4-carbon aliphatic chain. In this figure is not reported PES, as this polymer does
not have the same crystal form and peak positions as the PEES-based copolymers of
the present work (see Table A.2.1 of the Annexes for a detailed list of peak positions),
and this diagram, which has been previously reported in the literature, would add
little to the discussion here. All other polymers are crystalline to various degrees. The
degree of crystallinity χx−ray was calculated from the relative intensities of the
66
amorphous and crystalline peaks in X-ray diffraction and is reported in Table 2.3. In
all cases, the benzyl alcohol/CH2Cl2 solvent increases crystallinity.
The most impressive increase in crystallinity is noted for PAH-8EES, which did not
crystallize upon synthesis, but becomes the most crystalline polymer (50%
crystallinity) after solvent treatment.
In all cases, peak positions before and after recrystallization remain the same, and so
do relative intensities, although changes occur related to the presence of an important
amorphous halo in poorly crystallized samples. More significantly, peak widths
decrease due to the improvement in crystal phase perfection and in crystallite size,
allowing for a better peak resolution.
As before recrystallization, ADMET PA-4EES and polycondensation trans
copolymer PTA-4EES have almost superimposable diffraction diagrams, indicating
that the decrease in dispersity does not affect noticeably crystallization for this
molecular weight range.
In terms of crystal form, various distinct diagrams are observed. PTA-4EES and
PTA-8EES have a completely different diffraction diagram. Neither corresponds to a
known form of PES, but unfortunately comparison to PEES could not be made, no X-
ray diffraction diagram ever having been obtained to the best of our knowledge for
this polymer.
Observation of a different crystalline form for the 4-ring polymer can be due to
incorporation of the trans-allyl group into the crystallographic repeat unit, the
polymer thus behaving as a different homopolymer, due to the length of the regular
block EES which is very short. This is confirmed by comparing with the diffraction
diagrams of the hydrogenated, chlorinated and brominated copolymers, which are
markedly different, reflecting different crystallographic repeat units and/or packings.
On the other hand, the PTA-8EES and its hydrogenated counterpart have the same
structure, peak positions and relative intensities matching, indicating in this case that
67
the allyl group and the aliphatic chain are excluded from the crystallographic repeat
unit and are therefore segregated in the interlamellar region.
The 4-carbon segment of hydrogenated polymers increases the flexibility of the chain
and entropy of the system, and becomes a better position for chain folds and
reorganization to occur, thus favoring crystallization. On the other hand, trans-allyl
also favors crystallization. Chlorination and bromination result in intermediate
crystallization, thus indicating that packing may be disrupted by steric hindrance.
Molecular models were built to verify whether cis and trans-allyl groups could both
lead to chain folding, and representative examples are shown in Figure 2.6. Models
built show that both the cis and trans groups can lead to chain folding. In both cases,
the number of conformations leading to such chain folds is limited, and a very narrow
window of torsion angles must be adopted, limiting the probability for folding to
occur in such a close packed way. Energies of the trans and cis isomer folds are
similar (6.8 kcal mol-1 for the lowest energy fold built for the cis isomer, and 6.4 for
the trans isomer), but result in small interplanar ring distances (from 3.7 to 5.3 Å
approximately), restricting these chain folds to crystal structures that allow such close
packing. As various pieces of evidence point to the existence of a helical
conformation for PES25 and PEES, such folds may not at the required geometry for
the adopted crystal structures. On the other hand, cis and trans-allyl groups also affect
relative chain alignment, as depicted in Figure 2.6b: due to their geometry and to
unfavorable H/H contacts, cis conformers do not allow a coplanar segment to form,
and chain bifurcation ensues, which may be a reason why this group inhibits
crystallization. On the other hand, trans segments can form extended conformations,
thus favoring chain alignment, leading to the occurrence of pre-crystalline aggregates
which may be precursors to the crystalline phase, in agreement with the theories
proposed by Allegra and Meille27 and by Strobl.28 Finally, the more rigid PAE-4EES
copolymer shows a good crystallinity, thereby indicating that the addition of a rigid
segment next to the EES block favors crystallization
68
a) b)
Figure 2.6: Molecular models of chain folding due to allyl groups: (a) chain fold
models and (b) extended chain conformation, showing deviation from linearity
2.2.10 Double melting behaviour
PA-4EES is the only polymer in this study to exhibit a double melting behaviour,
which is in itself surprising, as PTA-4EES is structurally very similar, with however a
higher dispersity and approximately 4% more cis content. Changes in relative
endotherm intensity of the two peaks have been noted from one synthesis to another,
as shown in Figure 2.7a. These could not be associated with any specific synthesis
conditions or measured properties, and are attributed to random variations during
precipitation conditions.
The double melting behaviour is common to many semicrystalline polymers, and may
be caused by the melting of a secondary structure within the spherulite,29 or to
phenomena such as metastable crystals, secondary crystallization, occurrence of
crystal populations with different crystal forms, shapes, sizes or perfection.30–35 In
order to determine what this double melting endotherm corresponded to in the present
case, samples were heated between Tm1 and Tm2 and then quenched, and the resulting
samples were analyzed by X-ray diffraction, as illustrated in Figure 2.7b. Under these
conditions, the amorphous halo has grown considerably in intensity, denoting partial
melting of the samples. Diffraction peaks remain, as first glance, at the same position
69
as the initial sample. However, the relative intensities of the peaks vary in the 15 to
22° region. Further, the shoulder at 21.5° shifts to 21.0° and becomes a clearly
distinct peak and a new, weak intensity peak appears at 37.5°. These changes indicate
that a slightly different crystal form is present. Further work will be necessary to
ascertain whether this crystal form was present before partial melting but went
undetected due to the similarity in peak positions, or whether a change in the crystal
form occurs during partial melting.
a)
b)
Figure 2.7: Investigation of the double melting behaviour of PA-4EES
a) Representative DSC scans of PA-4EES and b) X-ray diffraction diagrams as
synthesized and after Annealing between Tm1 and Tm2 and rapid quenching
70
2.3 Conclusion
In this work, the objective was to synthesize PEES with an allyl group regularly
inserted in its backbone, and to obtain copolymers which could crystallize and which
could be subjected to post-functionalization reactions, allowing a rapid and
straightforward change in properties. Two synthetic pathways were used: ADMET
polymerization using a Grubbs second generation catalyst or a Hoveyda–Grubbs
catalyst, and traditional step-growth polycondensation.
Regular trans-allyl containing semi-crystalline PEES-based copolymers of moderate
molecular weight and low dispersity were synthesized by ADMET. Polycondensation
was used to obtain cis-allyl and trans-allyl copolymers of relatively low molecular
weights, but higher polydispersities. Even higher molecular weights but also
polydispersity were obtained by replacing the ether linkage between the EES and
allyl groups by an ester linkage. Post-modification was demonstrated by using
hydrogenation, chlorination and bromination reactions, which occurred with more
than 99% yield.
Modulation of crystallization upon design of the chain sequence by regularly
inserting allyl groups was demonstrated. Crystallinity could be totally suppressed by
using cis-allyl groups, whereas incorporation of trans-allyl groups regularly inserted
along the main chain favors crystallization. The 4-ring EES allyl block was too short
for the crystal structure of PEES to be adopted, and instead insertion of the trans-allyl
group in the crystallographic repeat unit occurs, as demonstrated by the change in
diffraction diagram upon hydrogenating this polymer. This is in agreement with a
non-trans conformation of ethersulfone polymers, as proposed previously,25 which
may require more than a single repeat unit for a helix conformation to be adopted.
Changes in the allylic spacer therefore allow partial control of crystallization of this
polymer, and further modulations will be attempted in future work by attaching
various groups at the allyl position, thus investigating the effect of steric hindrance or
of specific interactions.
71
2.4 Acknowledgements
The authors wish to acknowledge the financial support of NSERC (Natural Sciences
and Engineering Research Council of Canada). Help from Pierre Audet (NMR
spectroscopy) and Rodica Plesu (SEC, DSC) of the Département de chimie,
Université Laval is also gratefully acknowledged.
72
2.5 References
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2. Yang Y. S., Shi Z. Q., Holdcroft S., Eur. Polym. J. 2004, 40, 531.
3. Yi Z., Shu L., Cheng L., Zhu B., Xu Y., Polymer 2012, 53, 350.
4. Huang B., Zhu M., Cai M., J. Appl. Polym. Sci. 2011, 119, 647.
5. Hayakawa T., Goseki R., Kakimoto M.-A., Tokita M., Watanabe J., Liao Y.,
Horiuchi S., Org. Lett. 2006, 8, 5453.
6. Colquhoun H. M., Williams D. J., Acc. Chem. Res. 2000, 33, 189.
7. Manet S., Tibirna C., Boivin J., Delabroye C., Brisson J., Macromolecules 2006,
39, 1093.
8. Benoit J.-M., Furtos A., Hudon F., Provencher S., Brisson J., J. Macromol. Sci.,
Part A: Pure Appl. Chem. 2012, 50, 615.
9. Chen Y., Baker G. L., Ding Y., Rabolt J. F., J. Am. Chem. Soc. 1999, 121, 6962.
10. Blundell D. J., Osborn B. N., Polymer 1983, 24, 953.
11. Khatyr A., Maas H., Calzaferri G., J. Org. Chem., 2002, 67, 6705.
12. Plietker B., Niggemann M., Pollrich A., Org. Biomol. Chem. 2004, 2, 1116.
13. Paquette L. A., Fabris F., Tae J.,. Gallucci J. C., Hofferberth J. E., J. Am. Chem.
Soc. 2000, 122, 3391.
14. Tindall D., Pawlow J. H., Wagener K. B., in Alkene Metathesis in Organic
Synthesis, ed. A. F¨urstner, Springer Berlin Heidelberg 1999, vol. 1, pp. 183–
198.
15. Wagener K. B., Brzezinska K., Anderson J. D., Younkin T. R., Steppe K.,
DeBoer W., Macromolecules 1997, 30, 7363.
16. Yang J., Tyberg C. S., Gibson H. W., Macromolecules 1999, 32, 8259.
17. Chum S. P., Knight G. W., Ruiz J. M., Phillips P. F., Macromolecules 1994, 27,
656.
18. Napolitano R., Pirozzi B., Macromolecules 1998, 31, 3626.
19. Jones N. A, Sikorski P., Atkins E. D. T., Hill M. J., Macromolecules 2000, 33,
4146.
20. Ungar G., Xian-bing Z., Chem. Rev. 2001, 101, 4157.
21. Johnson R. N., Farnham A. G., Clendinning R. A., Hale W. F., Merriam C. N., J.
Polym. Sci., Part A: Polym. Chem., 1967, 5, 2375.
22. Mamo A., Aurelinano A., Battioto S., Cicala G., Samperi F., Scamporrino A.,
Recca A., Polymer 2010, 51, 2972.
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23. Rose J. B., Polymer, 1974, 15, 458.
24. Kitipichai P., Peruta R. L., Korenowski G. M., Wnek G. E., J. Polym. Sci., Part
A: Polym. Chem. 1993, 31, 1365.
25. Benhalima A., Hudon F., Koulibaly F., Tessier C., Brisson J., Can. J. Chem.,
2012, 90, 880.
26. Blackadder D. A., Ghavamikia H., Windle A. H., Polymer 1979, 20, 781.
27. Allegra G., Meille S. V., Adv. Polym. Sci. 2005, 191, 8.
28. Strobl G., Prog. Polym. Sci. 2006, 31, 398.
29. Gardner K. H., Hsiao B. S., Matheson Jr R. R., Wood B. A., Polymer 1992, 33,
2483.
30. Righetti M. C., Di Lorenzo M. L., J. Polym. Sci., Part B: Polym. Phys. 2004, 42,
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31. Yasuniwa M., Tsubakihara S., Ohoshita K., Tokudome S. I., J. Polym. Sci., Part
B: Polym. Phys. 2001, 39, 2005.
32. Yasuniwa M., Tsubakihara S., Murakami T., J. Polym. Sci., Part B: Polym. Phys.
1999, 38, 262.
33. Tan S., Su A., Li W., Zhou E., J. Polym. Sci., Part B: Polym. Phys., 1999, 38, 53.
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Polym. Phys., 2003, 42, 25.
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74
Chapitre 3: Synthesis of High Molecular Weight
Polyetherethersulfone - Allyl Copolymers of
Controlled glass transition
Adrien Faye, Alexandra Furtos and Josée Brisson
Article à soumettre
75
Résumé
Des polyétheréthersulfones (PEES) ayant des doubles liaisons insérées le long de la
chaîne principale du polymère ont été synthétisés par polycondensation. Les
températures de transition vitreuse ont été modulées par l'augmentation de la
longueur du bloc rigide (étheréthersulfone) et la diminution de celle du segment
flexible qui contient la double liaison. Les copolymères résultants ont des masses
molaires allant jusqu'à 60.000 g.mol-1 et des indices de polydispersité (Ip) peu élevés
(1,70 à 2,11). La distribution aléatoire des monomères dans ces copolymères a été
démontrée par spectrométrie de masse MALDI-TOF et par calorimétrique
différentielle à balayage (DSC), où l’on note une seule température de transition
vitreuse quel que soit le ratio bloc rigide/segment flexible. La résistance thermique
des copolymères augmente lorsqu’on diminue le pourcentage du segment flexible et
qu’on augmente celui du bloc rigide. La chromatographie d'exclusion stérique (SEC)
et les mesures de DSC montrent que la transition vitreuse augmente plus rapidement
avec l'augmentation de la rigidité de la chaîne du polymère qu’avec l'augmentation de
la masse moléculaire. Des films de copolymère ont été fabriqués et leur vieillissement
chimique a été étudié par immersion dans de l'eau de Javel, qui est couramment
utilisée pour nettoyer les membranes. Les films montrent une grande résistance à
l'eau de Javel, rendant ainsi ces copolymères utilisables pour la fabrication de
membranes.
76
Abstract
Polyetherethersulfones (PEES) with double bonds inserted along the main polymer
chain were synthesized by polycondensation. The glass transition was modulated by
extending the aromatic etherethersulfone rigid block and decreasing the length of the
flexible segment which contains the double bond. The resulting copolymers have a
Mn of up to 60,000 g/mol and moderate polydispersity index (Đ or Ip) of 1.70 to
2.11, and are shown by MALDI-TOF mass spectrometry and by the presence of a
single glass transition temperature in differential scanning calorimetry (DSC) to be
random in nature. The thermal resistance of copolymers increases when decreasing
the amount of the flexible segment and increasing the length of the rigid block. Size
exclusion chromatography (SEC) and DSC measurements indicate that the glass
transition increases faster with increasing polymer chain rigidity than with increasing
molecular weight. Copolymer films were manufactured and chemical aging was
investigated by immersion in bleach, which is commonly used to clean membranes.
They show high resistance to bleach, therefore making this approach relevant to
membrane fabrication.
77
3.1 Introduction
Polyethersulfone polymers (PES) and poly(etherethersulfones) (PEES) are widely
used in high-technology applications, such as membrane fabrication for syringe filters
or hollow fiber membranes for microfiltration, ultrafiltration or nanofiltration.1
Membranes made of polyethersulfones usually exhibit high selectivity (high rejection
rate) and a narrow distribution of pore size. They are very resistant to oxidation by
disinfectants such as peroxides or hypochlorites often used for cleaning membranes
after use,2 and can be operated over a wide pH range. They exhibit an excellent
thermal behavior, resisting up to 400 °C, and have glass transition temperatures
which can reach 200 °C.3 They also show interesting mechanical properties and can
easily withstand pressure gradients during filtration operations.
However, polyethersulfone homopolymers offer limited ranges in glass transition
temperatures (Tg), which can be detrimental to some applications. Controlling the
glass transition temperature can be determinant for improving the properties for
existing applications, but also helps to meet additional needs, including the
modulation of the membrane’s separating properties. It is therefore of interest to find
ways to modulate glass transition temperature of PES-based polymers.
PES was synthesized independently, and almost simultaneously by three laboratories:
Union Carbide Corporation4, 5 and 3M Corporation6 in the USA and by the Plastics
Division of ICI7 in the U.K. by two main routes8 using dipolar aprotic solvents such
as dimethylsulfoxyde (DMSO), 1-methyl-2-pyrrolidone (NMP) or dimethylacetamide
(DMAc). 3M Corporation synthesized PES by the polysulfonylation process, a
classical electrophilic aromatic substitution in which arylethers are coupled through
sulfone linkages by a Friedel-Crafts reaction. Union Carbide Corporation and the
Plastics Division of ICI prepared PES by polyetherification, which is a nucleophilic
substitution of activated aromatic dihalides in which sulfone groups are present in the
intermediates, and the ether linkages are formed by displacement reactions.9
78
Nowadays, the main method used for the synthesis of these polymers is
polycondensation by aromatic nucleophilic substitution at high temperature (180 °C)
generally using dimethylacetamide (DMAc).10 The synthetic route involving a
Friedel-Crafts polycondensation suffers from low reactivity and poor selectivity
compared to nucleophilic aromatic substitution.11
A PEES copolymer in which double bonds were regularly inserted along the
backbone was recently developed by our group, and can be synthesized either by
using acyclic diene metathesis polymerization (ADMET) or regular polycondensation
reaction.12
In the present work, the nucleophilic substitution polycondensation reaction was used
to obtain high molecular weight polyetherethersulfone (PEES) with double bonds
inserted in the polymer chain. Random copolymers were prepared with the aim of
controlling the glass transition temperature. Copolymer films were also prepared, and
their chemical aging was investigated by immersion in bleach.
3.2 Experimental section
3.2.1 Instrumentation
Nuclear magnetic resonance (NMR) spectroscopy measurements were performed in
CDCl3 or dimethyl sulfoxide-d6 solutions on a Bruker AMX 400 MHz at room
temperature.
Size exclusion chromatography (SEC) was carried out on a system composed of a
515 HPLC pump, two Agilent PL-Gel Mixed B-LS columns and a RI detector
Optilab 903 model coupled to a LASER Dawn DSP photometer. Monodisperse
polystyrene standards were used for calibration and N-methyl-2-pyrrolidone (NMP)
as eluent at a flow rate of 1.0 mL.min-1. Sample concentration was 5 mg mL-1 and
injection volume was 50 µL. Chromatograms were analyzed with the ASTRA
software version 4.70.07. (Wyatt Technology Corp.) Thermogravimetric analysis
79
(TGA) was performed on a Mettler TGA/SDTA851e/SF/1100 °C equipped with an
MT1 balance under nitrogen atmosphere. Glass transition (Tg) was determined as the
midpoint of the transition using a differential scanning calorimeter (DSC) DSC823e
apparatus from Mettler under nitrogen atmosphere. Indium was used to calibrate the
apparatus prior to use. Scan rate was 10 °C.min-1 and liquid nitrogen was used for
cooling purposes. The STARe software version 9.30 (Mettler Toledo) was used for
data acquisition and processing.
FTIR spectroscopy was carried out on a Thermo Nicolet Magna 850 Fourier
transform spectrometer (Thermo Scientific) equipped with a MCT (mercury cadmium
telluride) detector cooled with liquid nitrogen and a potassium bromide coated
germanium beam splitter i. A Golden-GateTM attenuated total reflection (ATR)
module from Specac Ltd. was used to record attenuated total reflection spectra on a
diamond crystal. The spectral region used covers the mid-infrared, from 750 to 4000
cm-1. All spectra were recorded with 128 interferograms at a resolution of 4 cm-1.
MALDI-TOF mass spectrometry was performed on an Ultraflextreme TOF/TOF
instrument from Bruker Daltonics, equipped with a smart beam laser (355 nm) and
operated in positive reflectron mode at a repetition rate of 1 kHz. The instrument was
calibrated using the monoisotopic mass of the following protonated peptide species:
Bradykinin (1-7) 757.39, Angiotensin II 1046.54, [Glu]-fibrinopeptide-B 1570.67,
ACTH (clip 1-17) 2093.08, ACTH (clip 18-39) 2465.19 and Insulin Chain B oxidized
3495.65. Copolymer samples and dithranol (the MALDI matrix) were dissolved in
dichlorometane at 1 mg/mL and 30 mg/mL respectively. The cationization agent was
a NaI 10 mg/mL solution in THF. A 40 μL aliquot of copolymer solution was mixed
with 20 μL matrix. A drop of this mixed solution was then spotted onto the MALDI
target plate which had been pre-spotted with the cationization agent solution. The
spots were air-dried at room temperature and mass spectra were collected between
m/z 700-10000. The instrument was controlled by FlexControl 3.4 software and data
was processed with FlexAnalysis 3.4, both from Bruker Daltonics.
80
3.2.2 Materials
Bis(4-fluorophenyl) sulfone (99%), 4-methoxyphenol (99%), boron tribromide
(BBr3, 99.9%), N-methyl pyrrolidone (NMP), Dithranol (98%) matrix substance for
MALDI-MS, were all supplied by Sigma Aldrich and used without further
purification. Methylene chloride (CH2Cl2, 99.9%), sodium bicarbonate (NaHCO3,
99.7%), hydroquinone (99%), were purchased from Fisher Scientific and used
without further purification. N,N-dimethylacetamide (DMAc, 99+%) was supplied
by ACP chemical Inc. and dried over magnesium sulfate (MgSO4) or sodium sulfate
(Na2SO4) prior to use. Anhydrous potassium carbonate (K2CO3, 99%) was supplied
by EMD.
3.2.3 Synthesis of the monomer: 4,4’-bis(4-hydroxyphenoxy)
diphenyl sulfone (HPDS)
The monomer was synthesized as reported in reference 12.
3.2.4 Polymers synthesis
3.2.4.1 PEES synthesis10
A round bottom flask (50 mL) containing a magnetic stirrer was charged with 2.432 g
(17.60 mmol) of anhydrous K2CO3, 2.034g (8.000 mmol) of bis(4-fluorophenyl)
sulfone (FPS) and (0.881 g, 8.00 mmol) of hydroquinone. To this mixture was added
10 mL of DMAc dried over MgSO4 or Na2SO4 and the resulting solution was heated
at 150 °C for 10 hours using an oil bath. Initial monomer concentration was fixed
between 1 and 1.6 mol L-1. After the reaction, the reaction mixture was allowed to
cool to room temperature and precipitated into water, filtered, washed with hot
aqueous sodium bicarbonate (NaHCO3) and NaCl solutions to remove the remaining
DMAc, and dried in vacuo for 24 hours at 80 °C.
81
3.2.4.2 Synthesis of poly(4EES-alt-cb) and poly(4EES-alt-tb)
A round bottom flask (50mL) containing a magnetic stirrer was charged with 1.402g
(10.142mmol) of anhydrous K2CO3, 2.003g (4.610mmol) of 4,4’-bis(4-
hydroxyphenoxy) diphenyl sulfone (HPDS)12 and 0.576 g (4.610mmol) of either (Z)-
1,4-dichlorobut-2-ene (Z-DCB) or (E)-1,4-dichlorobut-2-ene (E-DCB). To this
mixture was added 9.2mL of DMAc dried over MgSO4 or Na2SO4 and the resulting
solution was heated at 75 °C for 24 hours and for 120 °C for another 24 hours using
an oil bath. The initial monomer concentration was set at 1 to 1.6 mol L-1. After the
reaction, the polymers were washed and isolated as described for PEES. Resulting
polymers are named poly(4-etherethersulfone-alternate-cis but-2-ene), abbreviated
poly(4EES-alt-cb), when synthesized using Z-DCB and poly(4-etherethersulfone-
alternate-trans but-2-ene), abbreviated poly(4EES-alt-tb), when using E-DCB, as
shown in Scheme 3.1a.
82
a)
b)
Scheme 3.1: Synthesis of random and alternate copolymers: a) Poly(4EES-alt-cb)
and poly(4EES-alt-tb) alternate copolymers and b) Poly(6EES-ran-4EEScb) random
copolymer (one pot polycondensation reaction)
83
3.2.4.3 Synthesis of poly(6EES-ran-4EEScb)
A round bottom flask (50mL) containing a magnetic stirrer was charged with 0.608g
(4.400mmol) of anhydrous K2CO3, 0.869g (2.000mmol) of 4,4’-bis(4-
hydroxyphenoxy) diphenyl sulfone (HPDS),12 X% mol of bis(4-fluorophenyl) sulfone
(FPS) and Y% mol of (Z)-1,4-dichlorobut-2-ene (Z-DCB) (X and Y quantities used
are reported in Table 3.1). To this mixture was added 4mL of DMAc dried over
MgSO4 or Na2SO4 and the resulting solution was heated in an oil bath at 75 °C for 24
hours, and temperature was raised to 150 °C for an additional 24 hours. The product
was recovered as described for PEES. The resulting polymer is named poly(6-
etherethersulfone-random-4-etherethersulfone-cis but-2-ene) and abbreviated
poly(6EES-ran-4EEScb), as shown in Scheme 3.1b.
Table 3.1: Monomer ratios used in the synthesis of poly(6EES-ran-4EEScb)
mol% FPS mol% HPDS mol% Z-DCB
0 100 100
50 100 50
60 100 40
70 100 30
80 100 20
90 100 10
3.2.5 Copolymer film preparation
0.2 g of a copolymer was dissolved in 5mL of DMAc or NMP, the solution was
filtered, poured into a Petri dish and heated at 100 °C under a hood. After solvent
evaporation, water was added to help lifting the film off from the Petri dish.
3.2.6 Chemical aging studies
Copolymer films having around 5cm in diameter and 75µm thickness were immersed
for one week at room temperature in a commercial bleach solution with a pH adjusted
84
between 10 to 11 using NaOH and HCl. Commercial bleach was supplied by LAVO
PRO 6 company and contained about 26 000 ppm of chlorine.
3.3 Results and discussion
3.3.1 Optimization of the synthesis of poly(4EES-alt-cb) and
poly(4EES-alt-tb)
In this work, the main aim was to prepare copolymers for membrane formation with
varying glass transition temperature. For this purpose, a variation of a previously
developed approach in our group was used: incorporation of allyl groups along the
PES main chain, as shown in Scheme 3.1a.12 However, in the previous work and in
spite of having optimized the reaction temperature, relatively low molecular weights
(Mn = 8400 g/mol) had been obtained, and resulting polymers showed poor film-
forming properties. As the aim was to study the crystal form obtained, such low
molecular weight allowed a better crystallization and this did not cause problems. In
the present work, however, the aim being to prepare films, this was not acceptable.
The reaction was therefore reinvestigated and re-optimized. As reported previously12,
a simple increase in temperature did not raise the molecular weight. Changes in
heating ramp were therefore performed, along with an optimization of reaction time
and monomer concentration. It was found that a combination of higher monomer
concentrations and gradually increasing the temperature in two steps yielded higher
molecular weights, as seen in Table 3.2. Reactions performed at high temperature
resulted in thermal degradation of the monomer, evidenced by the presence of some
brownish to black color in the reaction medium, whereas reactions at low
temperatures resulted in low molecular weights. It was therefore decided to attempt
starting the reaction at a low temperature, where no degradation of the 1,4-but-2-ene
dichloride occurred, and raising to a higher temperature once the polymer chains
started to grow.
85
In the present work, the temperature was maintained at 75 °C for 24 hours and then
raised at 120 °C for additional 24 hours. As reported in Table 3.2, this allowed
obtaining high molecular weights (37,000 g mol-1 for the trans-but-2-ene containing
copolymer and of 64, 800 g mol-1 for the cis-but-2-ene containing copolymer. As in
our previous study12, higher molecular weights are obtained with the cis-containing
copolymer, which is attributed to the high solubility of this copolymer, allowing it to
react longer without precipitating in the solution. These alternated copolymers now
show good film-forming properties. Due to this ease in obtaining higher molecular
weights, and its resistance to thermal and solvent-induced crystallization, the cis-
moiety was selected for further synthesis studies. The related homopolymer
poly(etherethersulfone) (PEES), was also synthesized for comparison purposes.
Table 3.2: Number molecular weight (Mn), degree of polymerization (DP) and
polydispersity index (Ip) of Poly(4EES-alt-tb), Poly(4EES-alt-cb) and PEES
Tg (ºC) Mn (g/mol) DP Ip Yield
Poly(4EES-alt-tb) 118 37,000 66 1.70 77%
Poly(4EES-alt-cb) 113 64,800 113 1.99 93%
PEES 205 36,300 112 1.80 86%
As reported in Table 3.2, resulting copolymers have relatively low glass transition
temperatures (Tg), 113 °C for poly(4EES-alt-cb) and 118 °C for poly(4EES-alt-tb) as
compared that of PEES homopolymer which is 205 °C. These can be major
drawbacks when designing polymers for applications which necessitate high
operating temperatures. A method to modulate the glass transition temperature was
therefore sought.
86
3.3.2 One-pot synthesis of copolymers with longer rigid segments,
poly(6EES-ran-4EEScb)
In order to decrease the effect of the double bonds, polymers with longer rigid
segments were sought. However, as mentioned in our previous work12, although it is
possible to synthesize longer rigid monomers by protection/deprotection means, this
is time-consuming and costly.12 A more simple technique was therefore sought. The
one-pot polycondensation reaction reported in Scheme 3.1b was therefore tested. In
this approach, each HPDS block can react with either a bis(4-fluorophenyl) sulfone
(FPS) or a Z-DCB molecule. By keeping the percentage of HPDS equal to the sum of
FPS and Z-DCB, copolymers with high molecular masses and variable contents of
flexible allylic groups were prepared. However, this simple approach has a price:
polymers obtained are not alternate but can be either block or random. This would be
a problem if optimal crystallization was sought, as any deviation from regularity
decreases the ability of the polymer to assemble in crystal platelets. However, in this
case, this will be an added advantage, further reducing the probability for long-term
solvent or thermal induced crystallization.
Copolymers having ratios of 50/50 to 90/10 FPS and Z-DCB were synthesized. A
100/0 ratio corresponds to pure PEES, 0/100 to the poly(4EES-alt-cb) copolymer.
Values below 50% FPS were not used due to the resulting low glass transition
temperatures. The resulting copolymers have a distribution of rigid aromatic
ethersulfone blocks, which increases chain rigidity of the copolymer. Table 3.3
reports the 6EES/4EEScb ratios used, along with the glass transition temperature and
number average molecular weight. As expected, the glass transition temperatures
increase with EES (etherethersulfone) ratio, since this ratio is that of the most rigid
group. As molecular weight is very sensitive to stoichiometry in polycondensation
reactions, some random fluctuations in molecular weights are observed.
87
Table 3.3: DSC and SEC data of copolymers synthesized with varying 6EES/4EEScb
ratios
6EES/4EEScb ratios Tg (°C) Mn (g/mol) Ip Yield %
0/100 113 64,800 1.99 93
50/50 144 13,800 2.11 97
60/40 154 47,900 1.88 90
70/30 166 52,300 1.95 93
80/20 169 31,700 1.83 96
90/10 175 50,300 1.80 96
100/0* 205 36,300 1.80 86
* corresponding to the polyetherethersulfone homopolymer (PEES)
NMR spectra of the resulting random copolymers are reported in Figure 3.1. The f
and e peaks attributed to the allylic group and peak d corresponding to the aromatic
ring next to the allylic group clearly decrease in intensity when the percentage of the
allylic group (Z-DCB) decreases, thus confirming that the desired copolymers have
been obtained. It is however not possible, using NMR, to determine with certainty
whether the copolymers obtained are random or block in nature.
88
Figure 3.1: 1H-NMR spectra of poly(6EES-ran-4EEScb) random copolymers
3.3.3 MALDI-TOF investigation of the copolymers
MALDI-TOF mass spectrometry was used to investigate the randomness of the
reaction used in the one-pot synthesis. MALDI-TOF of oligomers has previously
been reported and similar conditions were used for the present copolymers.13, 14
89
Unfortunately, only the lower molecular weight species are observed, as seen in
Figure 3.2. This may be caused by preferential ionization or desorption of short
chains, in agreement with previously observed MALDI-TOF results which show, for
some polymers such as PES and PEK, a tendency to favor the ionization of lower
molecular weight species.14, 15 Spectra were also registered using N-methyl-2-
pyrrolidone solutions, with additions of various cationization agents (silver, sodium,
and lithium), but peaks showed even lower intensities and spectra were similar in
nature, but poorer in quality. Therefore, MALDI-TOF results were not used to
determine molecular weights or polydispersities. Nevertheless, they can provide
insights on whether the reaction is truly random at its onset, when the sort chains are
formed, or whether randomization occurs at a later stage.
Figure 3.2 shows representative MALDI-TOF spectra for the PEES homopolymer,
for the alternate copolymers and for the proposed random copolymers, whereas
additional random copolymer spectra are available as Supplementary material. In
both, the homopolymer and in the random copolymer in cases, a Gaussian shaped
distribution of fragments is observed, although this Gaussian is displaced toward low
molecular weights and therefore only half is present for the random copolymer. A
regular spacing is observed in both cases, and it corresponds to 324 m/z units for
PEES and 486 for the alternate copolymer. On the other hand, for the alternate
copolymer, no Gaussian distribution is ever observed. This could be due to poor
ionization or the species, resulting in a poor sampling of the molecular weights.
However, the fact that this is systematic, and that changes in relative intensities of the
fragments are observed with monomer ratio indicates that this may be related to the
nature of the copolymers themselves.
90
a)
b)
c)
Figure 3.2: Representative MALDI-TOF mass spectrum of synthesized copolymers: a)
PEES homopolymer b) Poly(4EES-alt-cb) and c) Poly(6EES-ran-4EEScb), ratio 70/30
91
Table 3.4: Proposed assignment for the main MALDI-TOF fragments of the
PEES homopolymer
Peaks Adducts m/z obs. m/z calc.
J3 [(EES)3-cyclic + Na]+ 995.00 995.12
J4 [(EES)4-cyclic + Na]+ 1319.00 1319.17
J5 [(EES)5-cyclic + Na]+ 1643.00 1643.21
J6 [(EES)6-cyclic + Na]+ 1967.10 1967.26
J7 [(EES)7-cyclic + Na]+ 2291.10 2291.30
J8 [(EES)8-cyclic + Na]+ 2615.20 2615.35
J9 [(EES)9-cyclic + Na]+ 2939.20 2939.40
J10 [(EES)10-cyclic + Na]+ 3263.20 3263.44
J11 [(EES)11-cyclic + Na]+ 3587.30 3587.49
J12 [(EES)12-cyclic + Na]+ 3911.30 3911.53
J13 [(EES)13-cyclic + Na]+ 4235.30 4235.58
J14 [(EES)14-cyclic + Na]+ 4559.30 4559.62
J15 [(EES)15-cyclic + Na]+ 4883.30 4883.67
J16 [(EES)16-cyclic + Na]+ 5207.40 5207.71
J17 [(EES)17-cyclic + Na]+ 5531.50 5531.76
J18 [(EES)18-cyclic + Na]+ 5855.70 5855.81
92
Table 3.5: Proposed assignment for the main MALDI-TOF fragments for the
poly(4EES-alt-cb) in the 1000 - 5000 g mol−1 range (only the most intense peaks are
reported in this Table)
Peaks Adducts m/z obs. m/z calc.
K2 [(AB)2-cyclic + Na]+ 995.00 995.21
K3 [(AB)3-cyclic + Na]+ 1481.00 1481.33
K4 [(AB)4-cyclic + Na]+ 1967.10 1967.44
K5 [(AB)5-cyclic + Na]+ 2453.20 2453.55
K6 [(AB)6-cyclic + Na]+ 2939.30 2939.67
K7 [(AB)7-cyclic + Na]+ 3425.30 3425.78
K8 [(AB)8-cyclic + Na]+ 3911.30 3911.89
K9 [(AB)9-cyclic + Na]+ 4397.70 4398.01
K10 [(AB)10-cyclic + Na]+ 4883.30 4884.12
For all the copolymers, masses were used to assign peaks to specific fragments, and
this assignment is reported in Tables 3.4 to 3.7. In these tables, for PEES, Jn peaks
are assigned to cyclic sodium adducts containing n repeat units (EES or
etherethersulfone), as shown in Scheme 3.2. The most intense peaks therefore
correspond to cyclic molecules, which may be due to their higher solubility of to their
easier cationization. The 324 m/z spacing therefore corresponds to the mass of the
EES repeat unit. The observed peak positions are all in good agreement with the
calculated adduct masses, as reported in Table 3.4.
93
Table 3.6: Proposed assignment for the main MALDI-TOF fragments for the poly(6EES-ran-
4EEScb) in the 1000 - 3500 g.mol−1 range (only the most intense peaks are reported in this
Table)
Peaks Adducts m/z obs. m/z calc.
N1 [(AB)2-cyclic + Na]+ 995.00 995.21
N2 [(ABAC)-cyclic + Na]+ 1157.00 1157.19
N3 [(AC)2-cyclic + Na]+ 1319.00 1319.17
N4 [(AB)3-cyclic + Na]+ 1481.10 1481.33
N5 [(ABABAC)d-cyclic + Na]+ 1643.09 1643.30
N6 [(ABACAC)d-cyclic + Na]+ 1805.10 1805.28
N7 [(AC)3-cyclic or (AB)4-cyclic + Na]+ 1967.10 1967.44
N8 [(ABABABAC)d-cyclic + Na]+ 2129.20 2129.42
N9 [(ABABACAC)d-cyclic + Na]+ 2291.20 2291.39
N10 [(AB)5-cyclic or (ABACACAC)d-cyclic + Na]+ 2453.20 2453.37
N11 [(AC)4-cyclic or (ABABABABAC)d-cyclic + Na]+ 2615.30 2615.53
N12 [(ABABABACAC)d-cyclic + Na]+ 2777.29 2777.51
N13 [(AB)6-cyclic or (ABABACACAC)d-cyclic + Na]+ 2939.29 2939.49
N14 [(ABACACACAC)d-cyclic
or (ABABABABABAC)d-cyclic + Na]+ 3101.20 3101.46
N15 [(AC)5-cyclic or (ABABABABACAC)d-cyclic + Na]+ 3263.19 3263.62
N16 [(AB)7-cyclic or (ABABABACACAC)d-cyclic + Na]+ 3425.30 3425.60
dThe position of B and C is random
94
a) Repeat unit of the PEES homopolymer and example of a cyclic adduct
b) Repeat unit of the poly(4EES-alt-cb) alternate copolymer and example of a cyclic
adduct
c) Repeat unit fragments of the random copolymers
(Note: A may react with B and /or C but B cannot react with C)
Scheme 3.2: Repeat units and molar masses of various copolymers reported in the
MALDI-TOF study
95
In the case of the alternate copolymer (Figure 3.2b), the main peak series observed
(peaks Kn) also correspond to cyclic sodium adducts. The observed spacing unit of
486 m/z units also corresponds to the repeat unit of the alternate copolymer (this
repeat being composed of a EES segment combined to the B but-2-ene segment, as
shown in Scheme 3.2b), which is larger in this case due to the addition of the flexible
but-2-ene segment, as illustrated in Scheme 3.2b. Again, the notation used is such that
n corresponds to number of repeat units in the ring or polymer. Smaller intensity
peaks are also observed, and these correspond to polymeric species with different
end-groups and cationization agent. For these, attributions are reported in Table 3.7.
The L peaks correspond to linear poly(4EES-alt-cb) species with H and Cl as end-
groups and H+ as the cationization agent, whereas M peaks correspond to a
poly(4EES-alt-cb) cyclic ions with Li+ as the cationization agent.
Random copolymer spectra are much more complex in nature than can be noticed at
first glance, and many different peak series are observed. The spacing observed of
162 m/z units does not correspond to that of any of the fragments making of the
repeat units, as shown in Scheme 3.2c. It however corresponds to the difference
between the B and C fragments, which is 162 m/z units, indicating that these two
segments occur randomly along the fragments, and therefore in agreement with a
random copolymer.
Detailed peak assignments appear below. It must first be noted that, in this case, the n
number does not correspond to the number of repeat units, contrary to the previous
two cases, but only to the sequence of appearance in the spectra. Attribution of the
most intense N peaks appears in Table 3.6. A first series of peaks, peaks N1, N4, N7,
N10, N13 and N16, correspond again to a cyclic sodium adduct of the (AB)n type
with a spacing of 486, and match those observed for the alternate poly(4EES-alt-cb)
copolymers. A second series is composed of peaks N3, N7, N11 and N15 and
corresponds to all-rigid (AC)n cyclic sodium adducts, with spacing of 648 m/z units,
and therefore some segments but not all also match those of the PEES spectrum. The
third series, peaks N2, N5, N6, N8, N9, N12 and N14, corresponds to sodium adducts
96
of cycles composed of random ABAC segments, with molar masses depending on the
actual number of B and C segments in the adduct. The three peak series will not have
the same relative intensities depending on the B/C ratio, which explains the relative
changes in intensity with B/C ratio, but also the absence of a simple gaussian
distribution. Additional peaks are assigned in Table 3.7, and correspond to lithium
adducts or to linear copolymers, as in the case of the alternate copolymer spectra.
Although MALDI spectra reveal only for small molecular weights fragments, the fact
that these small fragments are random in nature insures that, even at the
polymerization onset, at low temperatures, random chains were obtained. The
temperature was therefore high enough for B and C fragment to react with
approximately equal probability to the A fragments. As the subsequent increase in
temperature occurs when all monomer or almost have reacted, randomization at such
an early stage should insure that the higher molecular weight chain distributions also
exhibit randomization. It is concluded that the two temperature stage one-pot
polycondensation process described here effectively leads to random copolymers.
97
Table 3.7: Proposed assignment for additional MALDI-TOF fragments for the poly(4EES-alt-cb) and poly(6EES-ran-
4EEScb) in the 1000 - 4000 g mol−1 range
Peaks m/Z Obs.
m/Z calc. Adducts
Poly(4EES-alt-cb) Ratio
50/50
Ratio
60/40
Ratio
70/30
Ratio
80/20
Ratio
90/10
L2 1009.00
1009.21 [H-(AB)2-Cl + H]+
Y1
1116.90 1116.90 1116.90 1116.90 1116.21 [Cl-4A-4B-1C-Cl + 2H]+
P1 1141.00 1141.00 1141.00 1141.22 [(ABAC)-cyclic + Li]+
X1
1388.90 1388.90 1388.90 1388.90 1388.27 [H-5A-3B-2C-F + 2H]+
R1 1441.10 1441.10 1441.10 1440.70 1440.26 [Cl-5A-4B-2C-Cl + 2H]+
M3 1465.12
1465.35 [(AB)3-cyclic + Li]+
L3 1495.00
1495.32 [H-(AB)3-Cl + H]+
X2
1550.90 1550.90 1550.90 1550.90 1550.34 [H-6A-5B-1C-F + 2H]+
R2 1603.09 1602.90 1602.90 1602.90 1602.90 1602.33 [Cl-6A-6B-1C-Cl + 2H]+
P2 1627.10 1627.10 1627.33 [(ABABAC)-cyclic + Li]+
X3
1712.99 1712.99 1712.99 1712.31 [H-6A-3B-3C-F + 2H]+
R3 1765.00 1765.00 1765.00 1765.00 1765.00 1764.30 [Cl-B6A-4B-3C-Cl + 2H]+
S1 1838.10 1838.36 [H-7A-4B-2C-H + 2H]+
98
X4
1875.00 1875.00 1875.00 1875.00 1875.34 [F-3A-2B-2C-F + H]+
T1 1897.10 1897.32 [Cl-3A-2B-2C-F + Li]+
R4
1927.20 1926.28 [Cl-6A-2B-5C-Cl + 2H]+
M4 1951.20
1951.47 [(AB)4-cyclic + Li]+
L4 1981.30
1981.43 [H-(AB)4-Cl + H]+
X5
2037.10 2037.10 2037.10 2037.10 2037.32 [F-3A-1B-3C-F + H]+
R5 2088.90 2088.90 2088.90 2088.90 2088.90 2088.44 [Cl-7A-4B-4C-Cl + 2H]
X6
2199.00 2199.00 2199.00 2199.00 2198.34 [H-7A-1B-6C-F + 2H]+
T2 2221.0 2221.46 [Cl-4A-4B-1C-F + Li]+
R6 2250.90 2250.90 2250.90 2250.90 2250.90 2250.42 [Cl-7A-2B-6C-Cl + 2H]+
X7
2361.10 2361.10 2361.10 2361.10 2361.46 [F-4A-3B-2C-F + H]+
R7
2413.10 2413.10 2413.10 2413.10 2412.39 [Cl-8A-4B-5C-Cl + 2H]+
M5 2437.30
2437.58 [(AB)5-cyclic + Li]+
L5 2467.20
2467.55 [H-(AB)5-Cl + H]+
X8
2523.10 2523.10 2523.10 2523.10 2523.43 [F-4A-2B-3C-F + H]+
T3 2545.10 2545.41 [Cl-4A-2B-3C-F + Li]+
R8 2575.20 2574.37 [Cl-8A-2B-7C-Cl + 2H]+
X9
2685.10 2685.10 2685.10 2685.10 2685.41 [F-4A-1B-4C-F + H]+
R9
2737.20 2737.20 2736.44 [Cl-9A-4B-6C-Cl + 2H]+
99
Note: The number preceding A, B, and C corresponds to the number of each A, B and C segment, but does not indicate that
these are linked sequentially. In each case, it is impossible to distinguish between the fragments with the same overall
composition but with different segment alternation.
X10
2847.10 2847.10 2847.10 2847.10 2847.57 [F-5A-4B-2C-F + H]+
R10
2899.20 2899.20 2899.20 2899.20 2898.42 [Cl-9A-2B-8C-Cl + 2H]+
M6 2923.30
2923.69 [(AB)6-cyclic Li]+
L6 2953.30
2953.66 [H-(AB)6-Cl + H]+
R11
3060.20 3060.20 3060.49 [Cl-10A-4B-7C-Cl + 2H]+
X11
3171.20 3171.20 3171.53 [F-5A-2B-4C-F + H]+
M7 3409.50
3409.81 [(AB)7- Li]+
L7 3439.20
3439.78 [H-(AB)7-Cl + H]+
X12
3495.10 3495.10 3495.66 [F-6A-4B-3C-F + H]+
100
3.3.4 Thermal properties of copolymers
3.3.4.1 Thermogravimetric analyses
By decreasing the proportion of allyl groups, it was expected that thermal stability
would increase, as the aromatic moiety is much more heat-resistant than the flexible
allyl segment. Thermogravimetric analyses were performed under a nitrogen flow and
the results are reported in Figure 3.3. For the PEES homopolymer, the degradation
proceeds in one step and starts around 500 °C, while for the copolymers it proceeds in
two steps. For regular alternating copolymers (0/100 ratio), the flexible segments
which are less resistant to heat degrade first from 370 to 425 °C, whereas the rigid
aromatic part degrades at higher temperature, from 500 to 600 °C. By reducing the
proportion of flexible groups (Z-DCB) and increasing the rigid group ratio,
degradation temperatures increase from 370 °C for a Z-DCB (0/100 ratio) to 400 °C
for the 90/10 ratio. Upon decreasing the percentage of flexible segments, the weight
loss during the first degradation decreases, confirming that this first degradation
corresponds to that of flexible but-2-ene segments.
Figure 3.3: Thermogravimetric degradation curves of poly(4EES-alt-cb) (0/100),
PEES homopolymer (100/0) and random copolymers with varying 6EES/4EEScb
ratios
101
3.3.4.2 DSC measurements
Figure 3.4 shows the second heating curve recorded by differential scanning
calorimetry (DSC) on the random copolymers with a scan rate of 10 °C/min. In all
cases, no melt point was observed, in agreement with the previous observation that
the inclusion of cis double bonds inhibits crystallization12 and with the expected
effect of increasing block size randomness along the chain. The glass transition can
clearly be seen, in some cases exhibiting a relaxation peak related to the fast cooling
performed before registering the reported second temperature scan. Whereas the glass
transition temperature of the regular copolymer was considerably smaller than that of
the PEES homopolymer (113 °C vs 205 °C), random copolymers systematically have
a higher glass transition temperature, which is attributed to their lower allylic group
content.
In addition, for all the curves, only one glass transition temperature is observed, and
only limited peak enlargement can be noted, which is compatible with a random
copolymer: block copolymerization should have resulted in blocks with very
different glass transition temperatures (Tgs), and therefore either the appearance of
two Tgs for each copolymer, or a significant enlargement of the Tg of copolymers.
This should be especially visible for the poly(6EES-ran-4EEScb) 90/10 ratio, which
shows a glass temperature difference of more than 60 °C as compared to poly(4EES-
alt-cb).
As shown in Figure 3.5, upon decreasing the proportion of flexible segment (Z-
DCB), glass transition temperatures increase steadily, indicating that copolymers with
high rigidity and small flexibility were obtained. This change cannot be attributed to
variations in molecular weight from one synthesis to another, although such changes
may explain the observed variations in linearity. This variation in Tg is calculated
with eq(3.1) and approximately follows the Gordon-Taylor equation for a copolymer
as reported by Brostow16 :
102
eq(3.1) 𝑇𝑔 = 𝑥1𝑇𝑔1+ 𝐾𝐺𝑇(1− 𝑥1)𝑇𝑔2
𝑥1 + 𝐾𝐺𝑇(1−𝑥1)
where Tg is the glass transition of poly(6EES-ran-4EEScb), Tg1 and Tg2 are
respectively for poly(4EES-alt-cb) and PEES, x1 and x2 are respectively the mass
(weight) fraction of poly(4EES-alt-cb) and PEES in poly(6EES-ran-4EEScb)
copolymer, and a value of kGT = 0.35 was evaluated from a fit between experimental
data and this equation.
Changing the ratio of flexible spacers, as expected, allows modulating glass transition
temperatures. In this range of FPS ratios, glass transition temperatures are all above
100 °C, and this should provide ample thermal resistance for typical polyethersulfone
applications. As observed copolymers obey the Gordon-Taylor equation, it will be
possible to use this equation to adjust the ratio of monomers prior to synthesis to the
desired final Tg of the copolymer.
103
Figure 3.4: DSC curves of poly(4EES-alt-cb) (0/100), PEES homopolymer (100/0)
and random copolymers with varying 6EES/4EEScb ratios
104
Figure 3.5: Changes in glass transition temperatures with varying 6EES weight % in
poly(6EES-ran-4EEScb) copolymers
3.3.5 Chemical aging studies
The most frequent procedure for cleaning the membranes is a back flush with
detergents or bleach to remove particles and fouling. Unfortunately, the sodium
hypochlorite present in bleach, which is efficient to kill micro-organisms, can also
cause membrane degradation. Therefore, polymers which are used to make
membrane must be resistant to bleach. To simulate conditions used in the membrane
industry, chemical aging of copolymer films was performed. Prulho and coworkers2
have shown that the low oxidizability of PES in sodium hypochlorite solution can be
explained in great part by its chemical structure, as it bears no aliphatic groups and
therefore no labile hydrogen to allow chain radical oxidation processes. In the present
case, the but-2-ene segment has an aliphatic group, and the copolymer may be more
susceptible to degradation. Degradation studies are therefore reported for poly(4EES-
alt-cb), which contains a fraction of allylic and aliphatic bonds more susceptible to
degradation. SEC and FTIR spectra were performed on copolymer films after one
105
week immersion in bleach. SEC will inform us if there is cleavage or not of the
polymer chains and FTIR allowed us to have information on the presence or not of
new groups such as carbonyl.
Table 3.8: Number molecular weight (Mn) and polydispersity index (Ip) of
poly(4EES-alt-cb) and poly(6EES-ran-4EEScb) copolymers before and after
immersed in bleach
Copolymers Before immersed After immersed
Mn (g/mol) Ip Mn (g/mol) Ip
Poly(4EES-alt-cb) 64,800 1.99 65,300 1.84
Poly(6EES-ran-4EEScb) 80/20
ratio 31,700 1.83 34,100 1.91
Table 3.8 shows molecular weights and polydispersity indices of copolymers before
and after immersion in bleach. No significant change in molecular weight is observed
or polydispersity, indicating that there is no observable chain cleavage.
Infrared spectra are reported in Figure 3.6. These were scaled using the C-C aromatic
ring valence band at 1580 cm-1 which was considered not to change in intensity even
if degradation occurred. Upon oxidation, carbonyl or hydroxyl groups may be
generated, the most intense bands associated with this modification would appear in
the spectrum in the 1690 - 1750 cm−1 region (C=O valence vibration) and 3400 –
3600 cm-1 (O-H valence vibration). As seen in Figure 3.6, no significant changes are
observed in these spectral regions, thus confirming that oxidation has not taken place.
It is therefore concluded, on the basis of FTIR and SEC results, that no significant
oxidation occurs when exposing the random copolymers to bleach.
106
Figure 3.6: FTIR spectra of poly(6EES-ran-4EEScb) copolymer before and after
immersion in bleach: a) from 500 to 1900 cm-1 and b) from 2600 to 4000 cm-1
107
3.4 Conclusion
High molecular weight ethersulfone–allyl copolymers with double bonds inserted
randomly along the polymer chain have been synthesized by a one-pot
polycondensation process. The random nature of the polymers was demonstrated by
using MALDI-TOF mass spectrometry, although only lower masses appear to be
expressed using this technique. Randomness was confirmed by the observation of a
single, narrow glass transition temperature. The glass transition temperature was
modulated by changes in the allyl/aromatic ether sulfone ratio, which allows
widening their application range. Copolymers show resistance to oxidation by bleach,
used as a disinfectant for industrial membrane applications, making their use in
membrane filtration possible. As demonstrated in an earlier paper, the double bonds
present along the main chain can be used for further polymer modification.
3.5 Acknowledgements
The authors wish to acknowledge the financial support of NSERC (Natural Sciences
and Engineering Research Council of Canada). Help from Alexandra Furtos of
Université de Montréal (MALDI-TOF), Pierre Audet (NMR spectroscopy) and
Rodica Plesu (SEC, DSC) of the Département de chimie, Université Laval is also
gratefully acknowledged.
108
3.6 References
1. Amirilargani M., Sadrzadeh M., T. Mohammadi, J. Polym. Res. 2010, 17, 363.
2. Prulho R., Therias S., Rivaton A., Gardette J.-L., Polym. Degrad. Stabil. 2013,
98, 1164.
3. Yadav K., Morison K. R., Food Bioprod. Process. 2010, 88, 419-424.
4. Farnham A. G., Johnson R. N., British Pat. 1,078,234, 1963.
5. Johnson R. N., Farnham A. G., Clendinning R. A., Hale W. F., Merriam C. N., J.
Polym. Sci. Part A : Polym. Chem. 1967, 5, 2375.
6. Vogel H. A., British Pat. 1,060,546, 1963.
7. Jones M. E. B., British Pat. 1016245, 1962.
8. Ciobanu M., Marin L., Cozan V., Bruma M., Rev. Adv. Mater. Sci. 2009, 22, 89.
9. Maiti S., Mandal B. K., Prog. Polym. Sci. 1986, 12, 111.
10. Hayakawa T., Goseki R., Kakimoto M.-A., Takita M., Watanabe J., Liao U.,
Horiuchi S. Org. Lett., 2006, 8, 5453.
11. Yonezawa N., Okamoto A., Polym. J, 2009, 41, 899.
12. Faye A., Leduc M., Brisson J., Polym. Chem. 2014, 5, 2548.
13. Benoit J.-M., Furtos A., Hudon F., Provencher S., Brisson J., J. Macromol. Sci.,
Part A : Pure Appl. Chem. 2012, 50, 615.
14. Behrendt J. M., Benstead M., Chaplin A., Wilson B., Turner M. L.,
Macromolecules 2011, 44, 9054.
15. Schriemer D. C., Li L., Anal. Chem. 1997, 69, 4176.
16. Brostow W., Chiu R., Kalogeras I. M., Vassilikou-Dova A., Mater. Lett. 2008,
62, 3152.
109
Chapitre 4: Postfunctionalization by thiol-ene
click reactions of polyetherethersulfone-allyl
copolymers for applications in membrane
filtration
Adrien Faye, Jean-François Morin, Maria Cornelia Iliuta and Josée
Brisson
Article à soumettre
110
Résumé
Des copolyétheréthersulfones, comportant des groupements allyliques comme
espaceurs, ont été fonctionnalisés par greffage de molécules hydrophiles ou
hydrophobes sur des doubles liaisons en passant par les réactions thiol-ène clic. Cette
approche permet, d’une manière simple, de modifier les propriétés du copolymère
pour les adapter à des applications spécifiques, en particulier pour favoriser leur
utilisation dans la fabrication des membranes. Des polyéthylènes glycols (PEG) et des
chaînes aliphatiques en C8 ont été ainsi greffés. Il a été possible de faire réagir une
partie ou toutes les doubles liaisons. Il est également possible de réticuler les films
après fabrication à travers les doubles liaisons non réagies, ce qui permet de diminuer
la solubilité du copolymère, qui augmente après fonctionnalisation. Des mesures
d'angle de contact ont été effectuées sur les films résultants. Les résultats obtenus
indiquent que cette approche permet de moduler l’hydrophilicité des copolymères ou
de les rendre encore plus hydrophobes, selon la nature chimique de la molécule qui y
a été greffée. Les films obtenus sont également relativement résistants à des
températures élevées, ce rend cette approche pertinente pour la fabrication de
membranes.
111
Abstract
Polyetherethersulfone-Allyl copolymers were functionalized by thiol-ene click
reactions to graft hydrophilic or hydrophobic molecules onto the polymer chain,
thereby providing a flexible means of modifying the copolymer properties for use in
membrane fabrication or other applications. Polyethylene glycol (PEG) and aliphatic
C8 chains were thus added. Substitution of all double bonds was achieved, and
modulation of this percentage from 50 to 100% was also performed. Upon
incomplete double bond reaction, the remaining double bonds were used to crosslink
the film post-fabrication and therefore decrease its solubility, which is often a
problem with PEES-based polymers. The hydrophilicity of the resulting films was
investigated by contact angle measurements. This approach permits the modulation of
the hydrophilicity and can lead to solvent-resistant hydrophilic or hydrophobic films.
The resulting films are also relatively resistant to high temperatures, therefore making
this approach relevant to membrane fabrication.
112
4.1 Introduction
Polyethersulfone polymers (PES) are widely used in high-technology applications,
such as membrane fabrication for syringe filters or hollow fiber membranes for
microfiltration, ultrafiltration or nanofiltration.1 Membranes made of
polyethersulfones usually exhibit high selectivity (high rejection rate) and a narrow
distribution of pore size. They are very resistant to oxidation by disinfectants such as
peroxides or hypochlorites often used for cleaning membranes after use,2 and can be
used over a wide pH range. They exhibit an excellent thermal behavior, resisting up
to 400 °C, and have glass transition temperatures (Tg) which can reach 200 °C.3 They
have also interesting mechanical properties and easily withstand pressure gradients
during filtration operations.
In the dairy industry, cheese whey was long considered a waste by-product, but the
use of membranes such as polyethersulfone based membranes now allows to recover
it by separation into individual constituents of high nutritional quality (protein
concentrates for standardization of milk proteins, protein isolates, etc.).3 PES
membranes are also used for industrial production of drinking water, providing a safe,
effective and rapid method for removal of particles, turbidity and micro-organisms.4
However, the use of PES membranes is often limited by their hydrophobic nature,
which leads to membrane fouling by adsorption of proteins and natural organic matter
and by biofilm formation. These eventually block membrane pores and reduce their
flux performance.5-7 Scanning electron microscopy (SEM) observations made by
Wang and coworkers7 show the presence of particle aggregates in the form of a
biofilm on the membrane surface. The extent of adsorption depends on the types of
solute macromolecule/membrane interactions such as hydrogen bonding, dipole
interactions, van der Waals interactions, and electrostatic effects,8 but hydrophobic
interactions have been proposed to be the main factor enhancing protein adsorption
onto the membrane surface.9 When a protein molecule approaches and is in contact
with the surface of hydrophobic polymeric membranes, water molecules between the
113
protein and the membrane surface will be displaced. This causes the protein molecule
to lose its bound water and thus induces conformational changes in its structure,
which result in an irreversible adsorption of the protein onto the membrane surface.10-
11 To maintain membrane permeability and the selectivity, regular chemical cleaning
is required every 18-24 hours.12 This induces oxidative degradation of the membrane
which results in performance decay in many separation applications, significant
reduction in system productivity and increase in system operational cost.4, 11
To reduce this effect, increasing the hydrophilicity of the membranes has been
suggested in the literature.11, 13, 14 Modifying the hydrophilicity of the membranes can
reduce protein adsorption onto the membranes, which will then require less cleaning
up, therefore saving time and money. Further, hydrophilic membranes are easier to
clean since the adsorbed protein molecules are more easily removed from a
hydrophilic surface than from a hydrophobic one.3
One of the strategies used to improve polyethersulfone hydrophilicity is to blend it
with hydrophilic polymers such as polyethylene glycol (PEG). Blending is by far the
simplest method but has limited applicability due to limited miscibility of
hydrophobic and hydrophilic polymers,15 leading to phase separation during the
membrane manufacture. Further, such membranes have poorer mechanical properties.
Mohammadi's group16 showed that by mixing PES with polyacrilonitrile (PAN) in a
weight ratio of 70/30, two layers were observed by SEM, which changes greatly the
membrane structure and performance as compared to neat PES.
In the present paper will be explored the possibility of grafting different molecules
onto polyethethersulfone-allyl copolymer chains. A polyethethersulfone polymer in
which double bonds were regularly inserted along the backbone was recently
developed by our group using acyclic diene metathesis polymerization (ADMET) and
regular polycondensation.17 It was also shown that this double bond can be readily
functionalized to adapt the copolymer properties for specific applications.17 Thiol-
ene click reactions18, 19 are used to graft hydrophilic molecules such as PEG segments
114
and more hydrophobic chains such as C8 alkanes to tailor hydrophilicity of
synthesized copolymers.
4.2 Experimental section
4.2.1 Instrumentation
Nuclear magnetic resonance (NMR) spectroscopy measurements were performed in
CDCl3 or dimethyl sulfoxide-d6 solutions on a Bruker AMX 400 MHz at room
temperature.
Size exclusion chromatography (SEC) was carried out on a system composed of a
515 HPLC pump, two Agilent PL-Gel Mixed B-LS columns and a RI detector
Optilab 903 model coupled to a LASER Dawn DSP photometer. Monodisperse
polystyrene standards were used for calibration and N-methyl-2-pyrrolidone (NMP)
as eluent at a flow rate of 1.0 mL min-1. Sample concentration was 5 mg mL-1 and
injection volume was 50 µL. Chromatograms were analyzed with the ASTRA
software version 4.70.07.
Thermogravimetric analysis (TGA) was performed on a Mettler
TGA/SDTA851e/SF/1100 °C equipped with an MT1 balance under nitrogen
atmosphere. Glass transition temperature (Tg) was determined as the midpoint of the
transition using a differential scanning calorimeter (DSC) Mettler DSC823e apparatus
under nitrogen atmosphere. Indium was used to calibrate the apparatus prior to use.
Scan rate was 10 °C min-1 and liquid nitrogen was used for cooling purposes. The
STARe software version 9.30 was used for data acquisition and processing.
An optical contact angle analyzer (OCA 15 Plus, Future Digital Scientific Corp,
USA) was used to measure the contact angles of prepared films with water at 298.2 K
based on the sessile drop method. A small water droplet was deposited on the film
surface and the contact angle was determined from images acquired by a high
resolution camera. A thermostated chamber controlled the temperature using a
115
refrigerated/heating circulator with high precision external temperature control
(Julabo F25-ME). At least three droplets were dispensed on each tested film and a
mean value was reported. Data were measured with an average uncertainty of ±1°.
4.2.2 Materials
Bis(4-fluorophenyl) sulfone (99%), 4-methoxyphenol (99%), boron tribromide
(BBr3, 99.9%), N-methyl pyrrolidone (NMP), 2,2-dimethoxy-2-phenylacetophenone
(DMPA, 99%), 2-(2-(2-chloroethoxy)ethoxy)ethanol (96%), potassium thioacetate
(98%) were all supplied by Sigma Aldrich and used without further purification.
Methanol (99.9%), N,N-dimethylformamide (DMF, 98%), dimethylsulfoxide
(DMSO, 99.9%), methylene chloride (CH2Cl2, 99.9%), sodium bicarbonate
(NaHCO3, 99.7%), hydroquinone (99%), were purchased from Fisher Scientific and
used directly. N,N-dimethylacetamide (DMAc, 99+%) was supplied by ACP
chemical Inc. and dried over magnesium sulfate (MgSO4) or sodium sulfate (Na2SO4)
prior to use. Anhydrous potassium carbonate (K2CO3, 99%) was supplied by EMD.
Thiourea (CH4N2S, 99%) was supply by Riedel-de Haën.
116
Scheme 4.1: Synthesis of 2-(2-(2-hydroxyethoxy)ethoxy)ethanethiol (PEG2-thiol)
4.2.3 Synthesis of S-2-(2-(2-hydroxyethoxy)ethoxy)ethyl thioacetate
(scheme 4.1)20
A round bottom flask (100 mL) containing a magnetic stirrer was charged with 2-(2-
(2-chloroethoxy)ethoxy)ethanol (7.166g, 42.500 mmol, 1eq) and potassium
thioacetate (8.259g, 72.250 mmol, 1.7eq). To this mixture was added 30mL of DMF
dried over MgSO4 or Na2SO4 and the resulting solution was stirred at room
temperature for 5 hours. 50mL of water were then added and the solution was
extracted with methylene chloride. The organic phase was then washed with an
aqueous solution of NaHCO3 and finally with saturated NaCl to remove DMF. This
organic phase was then evaporated off leaving oil which was dried in vacuo for 8
hours at 60 °C to get a pale-yellow oil (6.09g, 29.24 mmol, 69% yield). 1H-NMR 400
MHz ((CDCl3), r.t.): δ 3.73 (t, 2H, 3J = 7.24 Hz), 3.61 (t, 8H, 3J = 7.24 Hz), 3.093 (t,
2H, 3J = 7.24 Hz), 2.95 (s, 1H), 2.34 (s, 3H) ppm;
13C-NMR 400 MHz (CDCl3), r.t.): δ 195.51, 72.46, 70.24, 70.21, 69.67, 61.61, 30.51,
28.67 ppm.
4.2.4 Synthesis of 2-(2-(2-hydroxyethoxy)ethoxy)ethanethiol (PEG2-
thiol) (scheme 4.1)21
S-2-(2-(2-hydroxyethoxy)ethoxy)ethyl thioacetate (5.730 g, 28.800 mmol) was
dissolved in methanol (30 mL). KOH (12 mL, 57.600 mmol, 2eq, 7.200 mol L-1) was
added and the mixture was then heated at 70 °C for 2 hours using an oil bath. The
solution was allowed to cool at room temperature, neutralized with HCl 2M and
extracted with methylene chloride (3 x 20 mL). The organic layer was then dried over
anhydrous magnesium sulfate, filtered, and evaporated off leaving pale-yellow oil
which was dried in vacuo for 8 hours at 40 °C to afford 2-(2-(2-
hydroxyethoxy)ethoxy)ethanethiol (3.45 g, 20.753 mmol, 76%).
117
1H-NMR 400 MHz ((CDCl3), r.t.): δ 3.73 (t, 2H, 3J = 7.099 Hz), 3.65 (t, 8H, 3J =
7.099 Hz), 3.08 (s, 1Hz), 2.71 (t, 3H, 3J = 7.099 Hz), 1.62 (s, 1H) ppm; 13C-NMR 400
MHz (CDCl3), r.t.): δ 72.81, 72.51, 70.25, 70.16, 61.60, 24.14 ppm.
4.2.5 Synthesis of the monomer: 4,4’-bis(4-hydroxyphenoxy)
diphenyl sulfone (HPDS)
The monomer was synthesized as reported by Faye and coworkers17
4.2.6 Polymers and copolymers used in this work
Polymer and copolymer synthesis have been described in Chapter 2 and 3. (Ref
article 2 non encore publié)
Scheme 4.2 : Polymers and copolymers used in this work
118
4.2.7 Post-functionalization of copolymers by thiol-ene click
reactions19
The copolymer was dissolved in methylene chloride or dimethyl sulfoxide (DMSO),
depending on its solubility, using a round bottom glass flask (100 mL) containing a
magnetic stirrer. One equivalent per double bond of thiol-terminated molecule and
0.3% mol of the radical initiator (2,2-dimethoxy-2-phenylacetophenone (DMPA)) per
mol of double bond was then added. The mixture was degassed under vacuum for 5
minutes and bubbled with nitrogen for 10 minutes. The reaction occurred readily at
room temperature by irradiation at λmax 365 nm27, 28 with a 40W UV lamp.
119
Table 4.1: Grafted and cross-linked molecules and their abbreviations
Grafted molecules Abbreviations Functionnalized copolymer
2-(2-(2-hydroxyethoxy)ethoxy) éthanethiol PEG2-thiol Poly(4EES-alt-cb)-graft-PEG2
2,2′-(ethylenedioxy) diethanethiol PEG2-dithiol Poly(4EES-alt-cb)-crosslink-PEG2
1,3-propanedithiol Pr-dithiol Poly(4EES-alt-cb)-crosslink-Pr
1-octanethiol C8-thiol Poly(6EES-ran-4EEScb)-graft-C8
Benzyl mercaptan Benzyl-thiol Poly(6EES-ran-4EEScb)-graft-Benzyl
Poly(ethylene glycol) methyl ether thiol, Mn = 800g/mol PEG16-thiol Poly(6EES-ran-4EEScb)-graft-PEG16
2,2′-(Ethylenedioxy) diethanethiol PEG2-dithiol Poly(6EES-ran-4EEScb)-crosslink-PEG2
120
a)
b)
Scheme 4.3: Thiol-ene click reactions onto poly(4EES-alt-cb) copolymer : a) PEG2-
thiol chain grafting and b) Pr-dithiol and PEG2-dithiol chains cross-linking
121
a)
b)
Scheme 4.4 : Thiol-ene click reactions onto Poly(6EES-ran-4EEScb) copolymer : a)
C8-thiol, Benzyl-thiol and PEG16-thiol chains grafting and b) PEG2-dithiol chain
cross-linking
122
For the poly(4EES-alt-cb) copolymer, the glass transition temperature is already low,
so long flexible (C8-thiol) chains were not grafted, as this would result in lower Tgs
and would affect the mechanical properties.
4.2.8 Solubility test of the cross-linked copolymer
A cross-linked copolymer film with a weight M1 was immersed during 24 hours in
NMP, in which the uncross-linked copolymer is completely soluble. The copolymer
film was then removed from the solvent and dried completely. The mass (M2) of the
dry film was measured. The percentage of solubility was calculated following
Equation (1).
% 𝑜𝑓 𝑠𝑜𝑙𝑢𝑏𝑖𝑙𝑖𝑡𝑦 = 𝑀1 − 𝑀2
𝑀1 × 100 𝑒𝑞(1)
4.2.9 CHNS Elementary Analysis
CHNS elementary analysis was performed on an organic elemental analyzer (Flash
2000, Thermo Scientific). Cystine, used as a standard sample, was put in a universal
soft tin container (100pc, outside diameter = 5 mm, height = 8 mm, volume = 157
μL), which also served as a blank sample. Around 0.5 mg of each sample was
encapsulated in the same type of container. In each case, three samples were
measured, and the reported error was calculated by using the Student’s test with a
95% probability.
The theoretical percentage of carbon element in the expected cross-link copolymer
was calculated as described in the following section, by supposing that there is either
a maximum of one graft or of two grafts attached per double bond, so the molecular
weight of the grated molecule is divided by two or one, respectively.
123
4.2.9.1 Cross-linking with 2,2′-(ethylenedioxy) diethanethiol (PEG2-dithiol)
4.2.9.1.1 Theoretical percentage calculation of carbon atoms contained in the
copolymer after cross-linking (poly(4EES-alt-cb)-crosslink-PEG2), considering
one chain grafted per double bond
The molecular weight of the PEG2-dithiol graft is: M (C6H14O2S2) = 182 g mol-1.
When PEG2-dithiol is grafted, it loses two hydrogen atoms and its molecular weight
becomes 180 g mol-1. The molecular weight of the uncross-linked copolymer unit is:
M (C28H22O6S) = 486 g mol-1.
The molecular weight of the cross-linked copolymer unit is equal to the sum of the
molecular weight of the uncross-linked copolymer unit (486) and the molecular
weight of PEG2-dithiol graft, divided by two (180/2) and a hydrogen atom is added:
M (C31H29O7S2) = 577 g mol-1.
If 𝑥 is the molar mass fraction of the cross-linked copolymer, and 𝑦 the molar mass
fraction, of the uncross-linked copolymer, the sum of the molar mass fractions 𝑥 and
𝑦 is given by, 𝑦 + 𝑥 = 1, and the molecular weight of the cross-linked copolymer is
given by 𝑛(577𝑥 + 486𝑦), where 𝑛 is the number of the cross-linked copolymer
repeat units.
The mass of carbon atoms in the cross-linked copolymer is then equal to 𝑛 (31 ×
12𝑥 + 28 × 12𝑦). The theoretical percentage (𝑎) of carbon atoms contained in the
copolymer after cross-linking is: 𝑎 =31×12𝑥 + 28×12𝑦
577𝑥 + 486𝑦× 100 and therefore:
𝑎 = 372𝑥 + 336𝑦
577𝑥 + 486𝑦× 100
If there are no cross-links, 𝑥 = 0, 𝑦 = 1 and 𝑎 = 69.1%
If all double bonds are cross-linked, 𝑥 = 1, 𝑦 = 0 and 𝑎 = 64.4%
The values obtained from the elemental analysis should therefore be between 64.4
and 69.1% if the approximation that a single chain grafted per double bond is valid.
124
4.2.9.1.2 Theoretical percentage calculation of carbon atoms contained in the
copolymer after cross-linking (poly(4EES-alt-cb)-crosslink-PEG2) considering
two chains grafted per double bond
Similarly, if two grafts are added per double bond, one must change the mass of the
grafted molecule from(180/2) to 180, and the molecular weight of the cross-linked
copolymer unit with the two grafts becomes M (C34H34O8S3) = 666 g mol-1 instead of
M (C31H29O7S2) = 577 g mol-1. The theoretical percentage (𝑎) of carbon atoms
contained in the copolymer after cross-linking in this case is: 𝑎 =34×12𝑥 + 28×12𝑦
666𝑥 + 486𝑦×
100 and therefore:
𝑎 = 408𝑥 + 336𝑦
666𝑥 + 486𝑦× 100
If there are no cross-links, 𝑥 = 0, 𝑦 = 1 and 𝑎 = 69.1%
If all double bonds are cross-linked, 𝑥 = 1, 𝑦 = 0 and 𝑎 = 61.2%
4.2.9.2 Cross-linking with 1,3-propanedithiol (Pr-dithiol)
4.2.9.2.1 Theoretical percentage calculation of carbon atoms contained in the
copolymer after cross-linking (poly(4EES-alt-cb)-crosslink-Pr)
Using the molar mass of the Pr-dithiol graft (M(C3H8S2) = 108 g mol-1), similarly,
one obtains:
If a single graft exists per double bond: 𝑎 =29.5×12𝑥 + 28×12𝑦
540𝑥 + 486𝑦× 100 and therefore:
𝑎 = 354𝑥 + 336𝑦
540𝑥 + 486𝑦× 100
If there are no cross-links, 𝑥 = 0, 𝑦 = 1 and 𝑎 = 69.1%
If all double bonds are cross-linked, 𝑥 = 1, 𝑦 = 0 and 𝑎 = 65.5%
125
And, if two chains are grafted per double bond: 𝑎 =31×12𝑥 + 28×12𝑦
592𝑥 + 486𝑦× 100 and
therefore:
𝑎 = 372𝑥 + 336𝑦
592𝑥 + 486𝑦× 100
If there is no cross-link, 𝑥 = 0, 𝑦 = 1 and 𝑎 = 69.1%
If all double bonds are cross-linked, 𝑥 = 1, 𝑦 = 0 and 𝑎 = 62.8%
4.2.10 Cross-link density measurements
Cross-link density measurements of the cross-linked copolymer were performed
using a swelling method described in a previous paper by Liang and coworkers.22 A
copolymer film was cut in a small piece, weighted and submerged in toluene.
Samples were allowed to swell for 72 hours at room temperature in a Petri dish which
was covered and protected from light to reach equilibrium. After 72 hours, excess
solvent was removed using a pipet without touching the swollen film pieces. Each
film piece was then lightly dabbed with absorbent paper and immediately weighted
accurately.
The cross-link density, which corresponds to the number of moles of cross-links per
gram of insoluble network, and the number average molecular weight between cross-
links (𝑀𝑐) were calculated using the following equations23, 24:
𝑀𝑐 = 𝜌𝑉𝑠(𝑉𝑝
13 −
𝑉𝑝𝑟
2)
−𝐿𝑛[(1 − 𝑉𝑝) + 𝑉𝑝 + 𝜒𝑉𝑝2]
where 𝜌 is the density of polymer (g cm-3) and 𝑉𝑠 is the molar volume of solvent (cm3
mol-1), given by: 𝑉𝑠 = 𝑀𝑠
𝑑𝑠, Ms is the molar mass of the solvent (g mol-1) and 𝑑𝑠 is
the density of solvent (g cm-3).
𝑉𝑝 is the volume fraction of the copolymer in the swollen gel at equilibrium, given by
126
𝑉𝑝 = 𝑚𝑝 × 𝑑𝑠
𝑚𝑝(𝑑𝑠 − 𝑑𝑝) + 𝑚𝑡 × 𝑑𝑝]
𝑚𝑝 is the weight of the copolymer before swelling
𝑚𝑡 is the weight of the copolymer after swelling (polymer + solvent) at equilibrium
𝑑𝑝 is the density of the copolymer (g cm-3)
𝑉𝑝𝑟 is the volume fraction of the copolymer in the relaxed network state i.e., when
cross-linking is introduced, and is related to 𝑉𝑝 by the following equation:
𝑉𝑝 + 𝑉𝑝𝑟 = 1
is the copolymer - solvent interaction parameter, given by:
𝜒 = 𝛽 +𝑉𝑠
𝑅𝑇(𝛿𝑠 − 𝛿𝑝)
where 𝛽 is the lattice constant, usually about 0.3423
𝑅 is the universal gas constant
𝑇 is the absolute temperature
𝛿 is the solubility parameter and the subscripts 𝑠 and 𝑝 refer to the solvent and
copolymer, respectively.
Finally, the molecular weight between chain entanglements is related to the cross-link
density by the following equation:
𝐶𝑟𝑜𝑠𝑠𝑙𝑖𝑛𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = 1
2 × 𝑀𝑐
where 𝑀𝑐 is the number average molecular weight between cross-links.
A value of 8.94 MPa1/2 was used for the solubility parameter of the toluene solvent.25
PES has a chemical structure similar to that of the copolymer studied here, and as a
first approximation, the values for PES reported by Rizwan and coworkers26 have
been used in this work: the density of PES (1.37 g cm-3), and the overall solubility
parameter of PES (24.19 MPa1/2).
127
4.2.11 Copolymer film preparation
0.2 g of a grafted copolymer was dissolved in around 5mL of DMAc or NMP, the
solution was filtered, poured into a Petri dish 5cm in diameter and heated at 100 °C
under the hood. After solvent evaporation, water was added to help peeling off the
film from the Petri dish. The films have around 5cm in diameter and 75µm in
thickness.
4.2.12 Cross-linked copolymer film preparation
After reaction, the solution was filtered and poured into a Petri dish to evaporate the
solvent. After evaporation, an insoluble film was obtained. It was immersed in water
and then methanol to remove impurities, and finally dried under vacuum at 60 ºC for
24 hours.
4.3 Results and discussion
4.3.1 PES and PEES
In this work, PES and PEES were synthesized to compare their hydrophilicity and
thermal properties with the synthesized copolymers.
Table 4.2: Number molecular weights (Mn), degree of polymerization (DP) and
polydispersity index (Ip) of synthesized polyethersulfone (PES) and
polyetherethersulfone (PEES)
Mn (g/mol) DP Ip Yield
PES 25,100 108 1.70 93%
PEES 36,300 112 1.80 86%
128
4.3.2 Alternate and random copolymer synthesis
Alternate and random copolymers were synthesized as described in Chapter 3 and
directly functionalized by thiol-ene click reactions. Their molecular weight,
polydispersity index, glass transition temperature and contact angles are reported in
Table 4.3.
4.3.3 Post-functionalization of copolymers by thiol-ene click reactions
Thiol-ene click reactions were performed to functionalize the copolymers synthesized
in this work using DMPA (2,2-dimethoxy-2-phenylacetophenone) as a photoinitiator,
as shown in Schemes 4.3 and 4.4. In this work, the goal of functionalization was to
make films with controlled hydrophilicity. The allyl double bond was therefore
functionalized using different molecules such as PEG2-thiol, PEG2-dithiol,
octanethiol, benzyl mercaptan, propanedithiol (Table 4.1), and hydrophilicity of
resulting copolymers was evaluated by contact angle measurements (Table 4.3).
After grafting PEG2-thiol onto poly(4EES-alt-cb) copolymer, FTIR spectra were
recorded to verify if the reaction had proceeded. FTIR spectra (Figure 4.1) were
normalized according to the intensity of the peak at 1586 cm-1, attributed to the
phenyl groups, which are expected to change in intensity after the reaction (Figure
4.1a). The FTIR spectrum of the functionalized copolymer (poly(4EES-alt-cb)-graft-
PEG2), represented by a full line (Figure 4.1b), shows an increase in the peak
intensity of the (C-H) stretching of aliphatic groups around 2900 cm-1, attributed to
the grafting of PEG2-thiol. The presence of a (OH) vibration around 3400 cm-1 is
further proof that the reaction has proceeded.
129
Table 4.3: Number molecular weight, polydispersity index, glass transition temperature and
contact angles of copolymers and functionalized copolymers
Copolymers Mn (g/mol) Ip Tg
(°C)
Contact
angle (°)
PES 25,100 1.70 236 88
PEES 36,300 1.80 205 82
Poly(4EES-alt-cb) 64,800 1.99 104 95
Poly(4EES-alt-cb)-graft-PEG2 9,000 2.10 83 69
Poly(4EES-alt-cb)-crosslink-PEG2 Insoluble insoluble 101 72
Poly(6EES-ran-4EEScb) 21,900 2.03 176 87
Poly(6EES-ran-4EEScb)-graft-C8 15,800 2.09 109 98
Poly(6EES-ran-4EEScb)-graft-Benzyl 22,100 2.21 127 94
Poly(6EES-ran-4EEScb)-graft-PEG16 12,800 2.09 95 60
Poly(6EES-ran-4EEScb)-crosslink-PEG2 partially
insoluble
partially
insoluble 92 78
For the Pr-dithiol, the resulting cross-linked polymer is partially soluble and degrades
at 130 °C before the glass transition temperature can be observed.
130
a)
b)
Figure 4.1: FTIR spectra of poly(4EES-alt-cb) and poly(4EES-alt-cb)-graft-PEG2: a) from 700
to 1900 cm-1 and b) from 2500 to 4000 cm-1
The reaction is also confirmed by NMR spectrometry (Figure 4.2) where a decrease
in intensity of peaks related to the double bond (e and f) is observed for the
poly(4EES-alt-cb)-graft-PEG2 copolymer as compared to that of the original
131
copolymer (poly(4EES-alt-cb)). The appearance of a peak around 3.4 ppm attributed
to the ethylene group of the grafted molecule confirms that PEG2-thiol is grafted onto
the copolymer through the double bond. From the integration of the NMR peaks of
both functionalized and original copolymers, it is found that 65% of double bonds
have reacted in the example reported in Figure 4.2.
Figure 4.2: 1H-NMR spectra of Poly(4EES-alt-cb) and Poly(4EES-alt-cb)-graft-
PEG2
It is possible to functionalize all double bonds by adjusting the amount of the
molecule to be grafted, as was demonstrated in Chapter 2. In the present work, this
was not the objective: some double bonds were needed to perform cross-linking
reactions after film fabrication, in order to increase their resistance to solvents, that is
to say decrease their solubility.
132
Using the same reasoning, it can be demonstrated that the PEG16 was grafted onto the
double bond of polymer chains by considering FTIR and NMR spectra of the original
and grafted copolymer (Figures 4.3 and 4.4).
All molecules represented in Table 4.1 were used for grafting or cross-linking.
Additional FTIR and NMR spectra confirming that grafting and cross-linking
procedures have been successful are reported in the supporting information.
a)
b)
133
Figure 4.3: FTIR spectra of Poly(6EES-ran-4EEScb) and Poly(6EES-ran-4EEScb)-
graft-PEG16 a) from 700 to 1900 cm-1 and b) from 2500 to 4000 cm-1
Figure 4.4: 1H-NMR spectra of Poly(6EES-ran-4EEScb) and Poly(6EES-ran-
4EEScb)-graft-PEG16
FTIR confirms that the cross-linking reactions were successful. Attempts at
quantification of the cross-linking were done using three methods:
1) Solubility decreased from 100% for the copolymer used for the cross-linking
reactions to 10% and 26% (Table 4.4) when, respectively, the PEG2-dithiol or the Pr-
dithiol was used to cross-link the polymer, which confirms that cross-linking has
occurred, but also indicates that part of the chains remain uncross-linked.
2) Swelling in toluene was used to estimate the molecular weight between
entanglements (Table 4.4). The difficulty in this case resides in determining the
correct values for the polymer solubility parameter and for the polymer density.
Values reported for PES26 were used in this case but this is an approximation, which
134
further varies in magnitude depending on the chemical nature of the cross-linking
agent used. Nevertheless, values obtained are in the order of 2000 g mol-1 for the
PEG2-dithiol and 3000 g mol-1 for the Pr-dithiol, which fits with the observation of a
higher solubility and therefore lower crosslink density achieved for the latter
polymer.
3) A final attempt to quantify the crosslink density was to use elementary analysis to
estimate compositional changes and correlate these to the addition of cross-links. The
theoretical percentage of carbon was calculated for a perfect, uncross-linked polymer
and for the same perfect polymer when 100% cross-links were added, both for the
PEG2-dithiol and Pr-dithiol cross-links. Two cases were considered: one cross-linking
per double bond, an hydrogen being attached also to the double bond upon reaction,
or two cross-links per double bond, which could correspond either to the chains being
attached by only one end, and therefore not consisting in a crosslink, or to chains
attached by both ends, but with two grafts attached by double bond, both possibilities
giving comparable carbon percentages.
Results shown in Table 4.4 indicate that a reasonable but not perfect fit between
observed and calculated values for the non cross-linked copolymer, the observed
quantity of carbon being lower than expected. This may be attributed to the presence
of imperfections in the copolymer or to inorganic impurities which would lower the
observed carbon content, therefore indicating that these measurements are semi-
quantitative.
Upon cross-linking, if only one cross-link is created per double bond, the percentage
of the carbon is expected to decrease for the both PEG2-dithiol and Pr-dithiol. If two
chains are attached by double bond, both carbon contents are expected to decrease.
Experimental values are lower for both cross-linked copolymers than for the original
uncross-linked copolymer, consistent with a reaction having occurred. Values are
lower than those calculated for the 100% cross-linked copolymer having one cross-
link per double bond, and show a better fit with values calculated for two double
cross-links per double bonds. Nevertheless, as in the case of the uncross-linked
135
copolymer, values are still lower than the expected minimum values that the
calculated values represent.
Although semi-quantitative, these values are consistent with a large proportion of
cross-links having been added to the copolymer.
Table 4.4: Carbon elementary analysis and solubility of copolymers cross-linked with
PEG2-dithiol and Pr-dithiol.
% carbon
obs.
% carbon calc.
(1 graft/double
bond)
% carbon calc.
(2 grafts/double
bond)
Solubility Mc
(swelling)
(g mol-1)
Alternating
copolymer 68.0 ± 0.5 69.1 69.1 100% -
Alternating
copolymer
cross-
linked with
PEG2-
dithiol
59.1 ± 0.5 64.4 61.2 10% 2000
Alternating
copolymer
cross-
linked with
Pr-dithiol
60.4 ± 0.5 65.5 62.8 26% 3000
4.3.4 Hydrophilicity and hydrophobicity studies
In order to evaluate the effect of the different modifications on copolymer
hydrophilicity, contact angles of PEES and of the original and functionalized
copolymers were measured. Static water contact angles of all samples are reported in
Table 4.3.
Figure 4.5 shows that the contact angle of PEES is smaller than that of PES,
indicating that PEES is more hydrophilic than PES. This result was expected as there
are more ethers (hydrophilic nature) in the PEES than in PES. This partly explains the
136
fact that PEES was chosen, the objective of this work being to increase the
hydrophilic nature of PES-based membranes to reduce clogging of the membranes.
It is noted in Figure 4.5 that, by grafting hydrophobic molecules such as alkyls onto
the poly(4EES-alt-cb) chain, contact angles of the resulting copolymers increase as
compared to that of PEES, indicating that hydrophilicity decreases. By grafting PEG
molecules which are hydrophilic, contact angles of resulting copolymers decrease as
compared to that of the original copolymer, and hydrophilicity increases. It is
therefore possible to decrease or increase the hydrophilicity of copolymers either by
grafting a hydrophobic or hydrophilic molecule, i.e. hydrophilicity can be modulated.
This result is very important because it indicates that it is possible to tailor the
properties of PEES copolymers for well-defined applications.
Figure 4.5: Contact angles of PES, PEES, alternate copolymer (Poly(4EES-alt-cb)),
and alternate copolymer after cross-linking or grafting
The same trend was also noted for random copolymers (Figure 4.6), but much longer
chains are then required to obtain the same effect since the number of double bonds,
137
and therefore of possible grafts, is smaller in the random copolymer than alternating
copolymer.
Figure 4.6: Contact angles of the random copolymer (Poly(6EES-ran-4EEScb))
before and after grafting or cross-linking
4.3.5 Film cross-linking
Cross-linking of already prepared films of Poly(6EES-ran-4EEcb) was performed to
compare their hydrophilicity and their solvent resistance with other copolymers
functionalized after complete dissolution (solution reaction). Due to the solid nature
of the film, it is supposed that cross-linking is mainly performed at the film surface,
although solvent penetration and therefore reactions are also possible in the whole
film thickness.
FTIR spectra presented in Figure 4.7 show that the reaction has taken place, as the
relative intensity of the (C-H) aliphatic vibration band has increased. It is also
noticed that, after reaction, the glass transition temperature increases from 148 °C to
138
153 °C at a scan rate of 20 °C/min, which also confirms that cross-linking has
occurred, as a cross-linked polymer will need more energy before the chains can
show long-range movement , hence a higher Tg is observed. The film also becomes
more hydrophilic after cross-linking, as the contact angle decreases from 87° (before
cross-linking) to 54° (after cross-linking). Finally, it becomes highly solvent resistant,
being insoluble even in NMP.
As compared to initial poly(6EES-ran-4EEScb)-crosslink-PEG2 (see Table 4.3)
functionalized with the same hydrophilic molecule (PEG2-dithiol), the cross-linked
copolymer film has a higher glass transition temperature (153 °C vs 92 °C) and a
lower contact angle (54° vs 78°), and is therefore also more hydrophilic.
Table 4.5: Glass transition temperatures and contact angles of Poly(6EES-ran-
4EEScb) before and after surface cross-linking
Poly(6EES-ran-4EEScb)
before surface cross-
linking
Poly(6EES-ran-4EEScb) after
surface cross-linking
Tg (°C) 148 153
Contact angle (°) 87 54
139
a)
b)
Figure 4.7: FTIR spectra of Poly(6EES-ran-4EEScb) before and after surface-
cross-linking
140
4.4 Conclusion
In this work, the aim was to functionalize poly(4EES-alt-cb) and poly(6EES-ran-
4EEScb) with hydrophilic or hydrophobic molecules to modulate their properties and
eventually those of PES-based membranes. Post-functionalization reactions were
carried out using the thiol-ene click reaction, allowing rapid and straightforward
changes in properties. Various chains were grafted, including hydrophobic 1-
octanethiol, 1,3-propanedithiol and benzyl mercaptan chains, as well as hydrophilic
PEG2-thiol, PEG2-dithiol and PEG16-thiol chains.
Cross-linking was investigated by FTIR, DSC, solubility and swelling measurements,
and finally CHNS analysis.
Contact angle measurements were performed on films prepared using these modified
copolymers, and show that hydrophilicity of these copolymers can be easily
modulated by this approach. This will allow to make hydrophilic membranes based
on polyethersulfones polymers, to prevent clogging during filtration of protein-
containing substances, and thus increasing the lifetime of resulting membranes.
Unfortunately, hydrophilic grafts also decrease Tg and increase polymer solubility,
which is detrimental to membrane properties. Cross-linking of film surface using
hydrophilic molecules was therefore performed to circumvent these problems. Films
were first prepared from solution evaporation, and then dipped into the reaction
mixture using methanol as solvent, after which they were submitted to thiol-ene click
reactions with a PEG2-dithiol. Resulting films shows a combination of increased
hydrophilicity, Tg and solvent resistance.
141
4.5 Acknowledgements
The authors wish to acknowledge the financial support of NSERC (Natural Sciences
and Engineering Research Council of Canada). Help from Maria-Cornélia Iliuta of
Génie chimique (contact angles measurements), Pierre Audet (NMR spectroscopy)
and Rodica Plesu (SEC, DSC) of the Département de chimie, Université Laval is also
gratefully acknowledged.
142
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3. Yadav K., Morison K. R., Food Bioprod. Process. 2010, 88, 419.
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5. Zhao W., He C., Wang H., Su B., Sun S., Zhao C., Ind. Eng. Chem. Res. 2011,
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6. Van der Bruggen B., Braeken L., Vandecasteele C., Sep. Purif. Technol. 2002,
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Biomed. Mater. Res. 1998, 39, 323.
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13. Liu S. X., Kim J.-T., J. Adhes. Sci. Technol. 2011, 25, 193.
14. Reddy A. V. R., Mohan D. J., Bhattacharya A., Shah V. J., Ghosh P. K., J.
Membr. Sci. 2003, 214, 211.
15. Van der Bruggen B., J. Appl. Polym. Sci. 2009, 114, 630.
16. Amirilargani M., Sabetghadam A., Mohammadi T., Polym. Advan. Technol.,
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17. Faye A., Leduc M., Brisson J., Polym. Chem. 2014, 5, 2548.
18. Bantchev G. B.,. Kenar J. A, Biresaw G., Han M. G., J. Agric. Food. Chem.
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19. Lluch C., Ronda J. C., Galià M., Lligadas G., Cadiz V., Biomacromolecules
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20. Wu S., Huang X., Du X., Angew. Chem., 2013, 125, 5690.
21. Sigma-Aldrich., Technical Bulletin AL-267, Thioacetate Deprotection
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22. Liang H., Hardy J.-M., Rodrigue D., Brisson J., Rubber Chem. Technol. , 2014,
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23. BarlkanI M., Hepburn C., Iran. J. Polym. Sci. Technol. , 1992, 1, 1.
24. Isabel E. P., Jesus M. M., Rosa G.-A. M., Inés F. P., J. Appl. Polym. Sci., 2007,
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25. Belmares M., Blanco M., Goddard W. A., III, Ross R. B., Caldwell G., Chou S.-
H., Pham J., Olofson P. M., Cristina T., J. Comput. Chem. 2004, 25, 1814.
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27. Dondoni A. Marra A., Chem. Soc. Rev. 2012, 41, 573.
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144
Chapitre 5 : Conclusion et Recommandations
Ce travail avait pour objectif de synthétiser les PES avec incorporation d’un
groupement post-fonctionnalisable pour contrôler la cristallinité, les températures de
transition vitreuse et l’hydrophilicité des copolymères résultants. Deux méthodes de
synthèse ont été utilisées : la polymérisation par métathèse des diènes acycliques
(ADMET) et la polycondensation classique. Au début du projet, nous comptions sur
l’ADMET pour synthétiser les copolymères mais plusieurs raisons ont fait que nous
avions ensuite utilisé la polycondensation. Une première raison est le coût du
catalyseur : Les catalyseurs de Grubbs nécessaires pour ce type de réaction sont assez
dispendieux, ce qui rend cette méthode de synthèse coûteuse. Cependant, la raison
principale est reliée aux limites de l’ADMET pour ce type de synthèse. D’une part, le
choix du solvant posait problème, d’autre part, certains groupements présents dans le
monomère pouvaient interagir avec le catalyseur et le désactiver. Les polymères ne
sont complètement solubles que dans les solvants polaires comme le NMP, le DMF,
le DMAc ou le DMSO, mais ces solvants interagissent tous avec les catalyseurs de
Grubbs, donc nous ne pouvions pas les utiliser. Nous avons alors utilisé le
dichlorométhane qui est un solvant approprié pour l’ADMET d’après Schulz et al.1
mais, à des taux de conversion élevés, le polymère devient partiellement soluble dans
ce solvant. Le flux d’azote imposé pour faire évaporer l’éthylène formé lors de la
réaction et éviter une réaction réversible cause également un problème car le
dichlorométhane s’évapore en même temps, laissant le milieu réactionnel dépourvu
de solvant.
Finalement, un autre facteur limitant concerne la liaison de coordination
intramoléculaire qui peut se créer entre les doublets libres de l’atome d’oxygène
proche de la double liaison et le métal central du catalyseur, ayant pour conséquence
la désactivation complète du catalyseur. Wagener et al.2 ont étudié la possibilité de la
formation de cette liaison intramoléculaire et ont conclu qu’il faudrait trois (3)
groupements méthylène entre l’oxygène et la double liaison pour éviter la formation
145
de ce complexe intramoléculaire. Dans le cas du polymère étudié ici, il y a un seul
groupement méthylène entre l’oxygène et la double liaison. Ceci explique les faibles
masses molaires obtenues, valeurs qui variaient peu avec la quantité de catalyseur
utilisée. Les taux de conversion sont également très faibles. En raison de ces faibles
masses molaires, nous étions incapables de fabriquer des films résistants avec ces
copolymères. Or, la principale application visée dans ce projet est la fabrication de
membranes, ce qui nécessite des polymères de masses molaires élevés. Nous n’avons
pas voulu augmenter la longueur du segment flexible pour ne pas compromettre les
propriétés mécaniques du copolymère résultant, et avons donc abandonné cette
méthode de synthèse dans les travaux subséquents.
Schéma 5.1 : Illustration de la possibilité d’une liaison intramoléculaire entre
l’oxygène proche de la double liaison et le métal central du catalyseur2
C’est ainsi que nous avons eu recours à la polycondensation classique en faisant
réagir un bloc rigide avec un monomère de configuration cis ou trans pour obtenir,
respectivement, un copolymère de configuration cis ou trans. Les monomères
flexibles utilisés pour la polycondensation sont accessibles et très économiques. Le
bloc rigide est facile à synthétiser avec des rendements de plus 90%. Son architecture
très simple permet de sauver une étape dans la synthèse en comparaison au
monomère utilisé pour l’ADMET. La synthèse par polycondensation nous a permis
d’obtenir des copolymères de hautes masses molaires (jusqu’à des Mn de plus 60 000
g.mol-1) avec des taux de conversion élevés.
146
Avec le monomère de configuration trans, le copolymère résultant est semi-cristallin
et la cristallinité peut être améliorée en recristallisant dans le dichlorométhane
contenant 10% d’alcool benzylique. Par contre, avec un monomère flexible de
configuration cis, la cristallisation est complètement inhibée même en recristallisant
par solvant. Les copolymères cis seraient très utiles pour la fabrication de membranes
pour la filtration où l’on note souvent un vieillissement des membranes par
cristallisation, matérialisé par des craquelures ou des fissures au niveau de la surface.
Les copolymères obtenus par polycondensation ont permis de confirmer la
configuration trans des copolymères obtenus par ADMET par comparaison des
spectres RMN. La cristallisation a été confirmé par diffraction des rayons X et
analyse enthalpique différentielle.
Avec la polycondensation, il est possible, non seulement d’introduire les doubles
liaisons dans les chaînes du polymère de façon parfaitement alternée comme dans le
cas de l’ADMET mais, également de façon aléatoire et à des ratios bloc
rigide/segment flexible modulables, ce qui est impossible de pouvoir se faire avec
l’ADMET. L’insertion du segment flexible de façon alternée dans les chaînes du
polymère a entraîné une baisse des températures de transition vitreuse (Tg) du
copolymère résultant. Ces Tg ont pu être améliorées par modulation du ratio bloc
rigide/segment flexible en utilisant une polycondensation en un seul pot.
Le fait de pouvoir moduler le rapport bloc rigide/segment flexible dans les chaînes du
polymère est un aspect intéressant car il nous donne la possibilité de pouvoir
contrôler les propriétés thermiques, notamment les températures de transition vitreuse
de ces matériaux. Nous avons ainsi montré qu’il est possible d’adapter les propriétés
thermiques de ces matériaux à des applications bien définies.
La spectrométrie de masse MALDI-TOF a permis de montrer que les copolymères
obtenus par variation du ratio bloc rigide/segment flexible sont de nature aléatoire et
non des copolymères blocs, ceci a été confirmé par DSC.
Nous avons également montré qu’il est facile de fonctionnaliser les copolymères par
des réactions thiol-ène clic pour orienter les propriétés vers des applications
147
spécifiques. Des chaînes hydrophiles sont greffées sur les doubles liaisons et les
mesures d’angles de contact ont montré qu’il est possible de contrôler l’hydrophilicité
de ces copolymères. Ce résultat est très important pour l'avenir des membranes à base
de PES, l’enjeu principal consistant à les rendre plus hydrophiles pour réduire le
colmatage lors des processus de filtration de certaines substances telles que les
protéines et, ainsi augmenter leur durée de vie.
Nous aimerions donner quelques recommandations sous forme de pistes
d’exploration pour la poursuite de ces travaux.
- Nous avons synthétisé des copolymères de hautes masses molaires capables de
former des membranes par inversion de phase mais nous n’avons pas pu faire des
essais de filtration, il serait souhaitable d’effectuer des tests de filtration avec ces
copolymères et de voir leur comportement.
- Les résultats de nos travaux ouvrent des perspectives intéressantes pour
l’utilisation des PES comme membrane échangeuse d’ion pour les piles à
combustible. Les PES dont des groupements sulfones sont rajoutés sur les cycles
aromatiques ont été proposés comme membranes échangeuses d’ions dans certaines
piles à combustible.3,4 Cependant, la sulfonation doit se faire localement et avec un
taux élevé d’unités sulfonées pour avoir une bonne séparation de phase, ce qui n’est
pas facile à obtenir. La séparation de phase permet d’avoir une bonne conductivité
protonique et de faibles coefficients de diffusion de la membrane.3,5 Dans le cas des
PES sulfonés, la séparation de phase provient de la différence de polarité entre les
unités hautement sulfonées et les parties hydrophobes du polymère (noyaux
aromatiques).4 Cependant, il est rapporté dans la littérature que des polymères avec
des groupements acides sulfoniques pendants (chaînes latérales) sont plus stables à
l'hydrolyse que ceux avec des fonctions acides sulfoniques directement connectées
sur le squelette des polymères.4
Il serait donc intéressant de greffer, sous forme de chaînes latérales, des chaînes
alkyles terminées par des groupements acides sulfoniques ou des chaînes alkyles
terminées par des fonctions ammonium. Ceci serait possible par les réactions thiol-
148
ène clic si l’autre extrémité de la molécule à greffer est terminée par une fonction
thiol. Les groupements acides sulfoniques et ammoniums serviront à la conductivité
protonique. Les chaînes alkyles devront être assez longues pour permettre une bonne
séparation de phase, et une optimisation sera à prévoir afin que la transition vitreuse
reste acceptable pour l’application visée.
149
5.1 Références
1. Schulz, M. D.; Wagener, K. B. ACS Macro Lett. 2012, 1, 449.
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3. Kerres, J. A. J. Membr. Sci. 2001, 185, 3.
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150
Annexes
Chapitre 2: Crystallization control of etherethersulfone copolymers by
regular insertion of an allyl functionality
Table A.2.1: Comparison of diffraction peak position for PES and polymers
synthesized in the present work
2θ
(º)
d
(Å)
PES
Form I *
PES
Form II*
PA-4EES
PTA-4AEES
Form I
PA-4EES
After
partial
melting
PAH-4EES PTA-8EES PAH-8EES
9.15 9.67 - - - - - w w
10.6 8.31 - - - - w - -
11.9 7.44 - - w - - w w
12.2 7.28 - - - - w - -
14.0 6.33 - w - - - - -
14.9 5.96 - - - - - w w
15.3 5.81 - - - - m - -
15.6 5.68 - - - - - - -
16.5 5.37 - sh m sh m - -
17.4 5.10 - - m s - vs vs
18.0 4.92 w m - - - - -
18.4 4.82 - - - - -
18.7 4.76 - - - - s - -
151
19.2 4.63 - - m s - vs vs
19.8 4.49 s - - - M - -
20.7 4.29 - s - - - sh sh
21.1 4.20 - - sh m - - -
21.9 3.96 - - s m - - -
22.5 3.96 - - - - M - -
22.8 3.90 m - - - - - -
23.4 3.80 - - - - - s s
23.7 3.76 - - - - m - -
24.5 3.63 m w m m - - -
25.8 3.45 - - - - m - -
26.5 3.36 s w - - - - -
27.8 3.21 - - m - m - -
28.8 3.10 - vw - - - w w
29.0 3.08 - - w w - - -
29.5 3.03 w - - - - - -
31.3 2.86 - - w - - - -
32.0 2.80 - - - - - - w
33.8 2.65 - - - - - - w
34.3 2.62 - - w - - - -
152
35.6 2.52 - - - - w - -
36.5 2.46 - - w - - - -
37.6 2.39 - - - - - w w
39.7 2.27 - - - - w - -
42.8 2.11 - - - - - w w
44.3 2.10 - - w w - - -
44.1 2.05 - - - - w - -
vs = very strong, s = strong, m = medium, w = weak, vw = very weak, sh = shoulder.
*Form I and Form II as reported by Blackadder and coworkers (Blackadder, D. A.;
Ghavamikia, H.; Windle, A. H. Polymer 1979, 20, 781)
153
Figure A.2.1: NMR spectra of 4,4’-bis(4-methoxyphenoxy) diphenyl sulfone
(MPDS) in CDCl3
154
Figure A.2.2: NMR spectra of 4,4’-bis(4-hydroxyphenoxy) diphenyl sulfone (HPDS)
in DMSO
155
Figure A.2.3: NMR spectra of 4,4’-bis(4-allyloxyphenoxy) diphenyl sulfone (APDS)
in CDCl3
156
a)
b)
Figure A.2.4: 1H-NMR spectrum of a) (Z)-1,4-dichlorobut-2-ene in CDCl3 and b)
(E)-1,4-dichlorobut-2-ene in CDCl3
157
Figure A.2.5: NMR spectra of 4-fluoro-4’-hydroxy diphenyl sulfone (FHDS)
158
Figure A.2.6: NMR spectra of 4-fluoro-4’-methoxy diphenyl sulfone (FMDS)
159
Figure A.2.7: NMR spectra of 4,4'-bis(4-(4-(4-
methoxyphenylsulfonyl)phenoxy)phenoxy) diphenyl sulfone (MPSPPDS) in CDCl3
160
Figure A.2.8: NMR spectra of 4,4'-bis(4-(4-(4-
hydroxyphenylsulfonyl)phenoxy)phenoxy) diphenyl sulfone (HPSPPDS) in DMSO
161
Figure A.2.9: 1H-NMR spectrum of poly(allyl-co-ether ether sulfone ether) (PA-
4EES) in CDCl3
a) Mn = 3300 g/mol
b) Mn = 6200 g/mol
162
163
164
165
Figure A.2.10: 1H-NMR of the 4-ring polymers obtained by polycondensation
a) Poly(trans-allyl-co-ether ether sulfone ether) (PCA-4EES)
b) Poly(cis-allyl-co-ether ether sulfone ether) (PTA-4EES)
c) Poly(hydrogenated allyl-co-ether ether sulfone ether) (PAH-4EES)
d) Poly(chlorinated allyl-co-ether ether sulfone ether) (PACl-4EES)
e) Poly(brominated allyl-co-ether ether sulfone ether) (PABr-4EES)
f) Poly(trans-allyl-co-ether ether sulfone ester) (PAE-4EES)
166
Figure A.2.11: Comparison of PTA-4EES NMR spectra before and after heating,
showing the persistence of the trans signals
a) Before heating
b) After heating
b)
167
M1 = 41 g/mol
M2 = 432 g/mol
M3 = 54 g/mol
If n is the number of M2 repeating units
Mn = 2*M1 + n*M2 + (n-1)*M3
Mn = 2*41 g/mol + n*432 g/mol + (n-1)*54 g/mol
Mn = n*486 g/mol + 28 g/mol
where n is determined by the intensity ratio of the 4.54 ppm polymer peak(e) to that
of the 4.58 ppm peak of the end-group (eEG) proton (e and eEG defined in Figure
A.2.9).
Schéma A.2.1: Mn calculation by NMR
168
Chapitre 3: Synthesis of High Molecular Weight Polyetherethersulfone
- Allyl Copolymers of Controlled glass transition
Figure A.3.1: Representative MALDI-TOF mass spectrum of Poly(6EES-ran-
4EEScb), ratio 50/50
Figure A.3.2: Representative MALDI-TOF mass spectrum of Poly(6EES-ran-
4EEScb), ratio 60/40
169
Figure A.3.3: Representative MALDI-TOF mass spectrum of Poly(6EES-ran-
4EEScb), ratio 80/20
Figure A.3.4: Representative MALDI-TOF mass spectrum of Poly(6EES-ran-
4EEScb), ratio 90/10
170
Chapitre 4: Postfunctionalization by thiol-ene click reactions of
polyetherethersulfone-allyl copolymers for applications in membrane
filtration
Figure A.4.1: NMR spectra of S-2-(2-(2-hydroxyethoxy)ethoxy)ethyl thioacetate in
CDCl3
171
Figure A.4.2: NMR spectra of 2-(2-(2-hydroxyethoxy)ethoxy)ethanethiol in CDCl3
172
a)
b)
Figure A.4.3: FTIR spectra of Poly(6EES-ran-4EEScb) and Poly(6EES-ran-
4EEScb)-graft-C8 a) from 700 to 1900 cm-1 and b) from 2500 to 4000 cm-1
173
Figure A.4.4: 1H-NMR spectra of Poly(6EES-ran-4EEScb) and Poly(6EES-ran-
4EEScb)-graft-C8
174
a)
b)
Figure A.4.5: FTIR spectra of Poly(4EES-alt-cb) and Poly(4EES-alt-cb)-crosslink-Pr
a) from 700 to 1900 cm-1 and b) from 2500 to 4000 cm-1
175
a)
b)
Figure A.4.6: FTIR spectra of Poly(4EES-alt-cb) and Poly(4EES-alt-cb)-crosslink-
PEG2 a) from 700 to 1900 cm-1 and b) from 2500 to 4000 cm-1
176
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