handbook of engineering and speciality thermoplastics · the handbook is to keep the practitioner...

Handbook of Engineering

and Speciality Thermoplastics

Volume 1 Polyolefins and Styrenics

Johannes Karl Fink Montanuniversität Leoben, Austria

Scrivener

)WILEY

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Handbook of Engineering and Speciality Thermoplastics

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Handbook of Engineering

and Speciality Thermoplastics

Volume 1 Polyolefins and Styrenics

Johannes Karl Fink Montanuniversität Leoben, Austria

Scrivener

)WILEY

Copyright © 2010 by Scrivener Publishing LLC. All rights reserved.

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Preface This volume on Polyolefins and Styrenics is the first part of a four-part set on Handbook of Engineering and Specialty Thermoplastics. The other three parts, to be published in late 2010 and 2011, are on Poly-ethers and Polyesters; Nylons; Water Soluble Polymers. The aim of the Handbook is to keep the practitioner abreast of the recent devel-opments in these subfields as well as to equip the advanced student with up-to-date knowledge as he/she enters the industrial arena.

This volume focuses on common types of polymers belonging to the class of polyolefins and styrenics. The text is arranged according to the chemical constitution of polymers and reviews the develop-ments that have taken place in the last decade. A brief introduction to the polymer type is given and previous monographs and reviews dealing with the topic are listed for quick reference. The text continues with monomers, polymerization, fabrication techniques, properties, application, as well as safety issues. Following this information, suppliers and commercial grades are presented.

Even though materials are ordered according to chemical struc-ture, a great variety of individual materials belonging to the same polymer type are discussed as well. In particular, the properties and safety data given should be considered as indicative. The reader who is actively engaged with the materials presented here should consult the technical data sheets and the material safety data sheets provided by the individual manufacturers.

How to Use this Book

Utmost care has been taken to present reliable data. Because of the vast variety of material presented here, however, the text cannot be complete in all relevant aspects, and it is recommended to the reader to study the original literature for complete information. For

v

vi

this reason, the author cannot assume responsibility for the com-pleteness and validity of, nor for the consequences of, the use of the material presented here. Every attempt has been made to identify trademarks; however, there were some that the author was unable to locate, and I apologize for any inadvertent omission.

Index

There are four indices: an index of trademarks, an index of acronyms, an index of chemicals, and a general index.

In the index of chemicals, compounds that occur extensively, e.g., "acetone", are not included at every occurrence, but rather when they appear in an important context.

Acknowledgements

I am indebted to our university librarians, Dr. Christian Hasenhüttl, Dr. Johann Delanoy, Dolores Knabl, Franz Jurek, Friedrich Scheer, Christian Slamenik, and Renate Tschabuschnig for support in lit-erature acquisition. I also want to express my gratitude to all the scientists who have carefully published their results concerning the topics dealt with here. This book could not have been otherwise compiled.

Last, but not least, I want to thank the publisher, Martin Scrivener, for his abiding interest and help in the preparation of the text and Jane Higgins for careful proofreading.

Johannes Fink 19th February 2010

Contents

Preface v

1 Metathesis Polymers 1 1.1 Monomers 2 1.2 Polymerization and Fabrication 2

1.2.1 Metathesis Reaction 3 1.2.2 Catalysts 7 1.2.3 Rate Controlling 14 1.2.4 Molecular Weight Regulating Agents 17 1.2.5 Polymers 17 1.2.6 Copolymers 18 1.2.7 Thermosets 19 1.2.8 Reinforced Polymer Composites 21 1.2.9 Polymers with Functional Groups 23 1.2.10 Poly(acetylene)s 25

1.3 Properties 26 1.3.1 Mechanical Properties 26 1.3.2 Optical Properties 26

1.4 Fabrication Methods 27 1.5 Fluorinated Polymers 27 1.6 Special Additives 28 1.7 Applications 29

1.7.1 Packaging Films 29 1.7.2 Wire Coating Materials 29 1.7.3 Chromatographie Supports 30

1.8 Suppliers and Commercial Grades 32 1.9 Safety 35 References 35

vu

viii Engineering Thermoplastics: Polyolefins and Styrenics

2 Cyclic Olefin Copolymers 41 2.1 Monomers 41 2.2 Polymerization and Fabrication 43

2.2.1 Catalysts 45 2.2.2 Metallocene Catalyzed Polymerization . . . . 47 2.2.3 Addition Polymerization 48 2.2.4 Thermosetting Resins 50 2.2.5 Analysis 51 2.2.6 Solvent Bonding 51

2.3 Properties 52 2.3.1 Mechanical Properties 52 2.3.2 Thermal Properties 52 2.3.3 Optical Properties 52 2.3.4 Barrier Properties 52 2.3.5 Chemical Resistance 53

2.4 Applications 53 2.4.1 Films 53 2.4.2 Optical Applications 54 2.4.3 Medical Applications 58 2.4.4 Packaging Areas 59 2.4.5 Absorption of Organic Contaminants 62 2.4.6 Adhesives in Semiconductor Technology . . . 63

2.5 Suppliers and Commercial Grades 65 2.6 Safety 65 2.7 Environmental Impact and Recycling 67 References 67

3 Ultra High Molecular Weight Poly(ethylene) 75 3.1 Monomers 75 3.2 Polymerization and Fabrication 76

3.2.1 Ziegler-Natta Catalysts 76 3.2.2 Mixed Catalysts 78 3.2.3 Single-Site Catalysts 79 3.2.4 Fractionation 80 3.2.5 Crosslinking 81 3.2.6 Fabrication 81 3.2.7 Porous Parts 82

3.3 Properties 82

Contents ix

3.3.1 Mechanical Properties 83 3.3.2 Electrical Properties 83 3.3.3 Optical Properties 83 3.3.4 Other Properties 83

3.4 Special Additives 83 3.5 Applications 84

3.5.1 Prosthetic Joints 84 3.5.2 Microporous Membranes 96 3.5.3 Binders for Filter Materials 99 3.5.4 Fibers 99

3.6 Suppliers and Commercial Grades 100 3.7 Safety 100 References 104

4 Poly(methyl)pentene 109 4.1 Monomers 109 4.2 Polymerization and Fabrication I l l

4.2.1 Ziegler-Natta Polymerization I l l 4.2.2 Metallocene Catalyzed Polymerization . . . . 112 4.2.3 Living Polymerization 114 4.2.4 Modification 114 4.2.5 Flash Spinning 116

4.3 Properties 118 4.3.1 Mechanical Properties 118 4.3.2 Thermal Properties 118 4.3.3 Electrical Properties 119 4.3.4 Optical Properties 119 4.3.5 Other Properties 119

4.4 Applications 120 4.4.1 Membranes 120 4.4.2 Heat Sealable Compositions 123 4.4.3 Laminates for Packaging Films 124 4.4.4 Overwrap Films 125 4.4.5 Image Forming Solution 126 4.4.6 Xerographic Devices 127 4.4.7 Acoustic Devices 128 4.4.8 Miscellaneous 129

4.5 Suppliers and Commercial Grades 132

x Engineering Thermoplastics: Polyolefins and Styrenics

References 133

5 Ionomers 137 5.1 Monomers 137 5.2 Polymerization and Fabrication 138

5.2.1 Processing 139 5.2.2 High Acid Types 139 5.2.3 Mechanisms of Crosslinking 140

5.3 Properties 143 5.3.1 Mechanical Properties 143 5.3.2 Thermal Properties 144 5.3.3 Electrical Properties 144

5.4 Special Additives 144 5.4.1 Antistatic Agents 144

5.5 Applications 145 5.5.1 Fuel Cell Anodes 145 5.5.2 Solar Control Laminates 145 5.5.3 Heat Seal Modifiers 146

5.6 Suppliers and Commercial Grades 146 References 148

6 Poly(isobutylene) 151 6.1 Monomers 151 6.2 Polymerization and Fabrication 152

6.2.1 Catalyst Systems 154 6.2.2 Polymerization Techniques 154 6.2.3 Poly(isobutylene) Grades 154 6.2.4 Star Shaped Polymers 155 6.2.5 Grignard Synthesis 156 6.2.6 End Group Functionalization 157 6.2.7 Blends and Composites 158 6.2.8 Halogenation Processes 161

6.3 Properties 161 6.3.1 Mechanical Properties 162 6.3.2 Thermal Properties 163 6.3.3 Electrical Properties 164 6.3.4 Optical Properties 165 6.3.5 Gas Permeation 165 6.3.6 Chemical and Physical Resistance 166

Contents χι


6.5.1 Drag Reduction Additives 167 6.5.2 Oil and Fuel Additives 167 6.5.3 Polymeric Antioxidants 170 6.5.4 Emulsifiers 173 6.5.5 Chewing Gums 174 6.5.6 Medical Applications 175 6.5.7 Pressure Sensitive Adhesives 176

6.6 Suppliers and Commercial Grades 177 6.7 Environmental Impact and Recycling 179 References 179

7 Ethylene Vinyl Acetate Copolymers 187 7.1 Monomers 187

7.1.1 Vinyl Acetate 189 7.2 Polymerization and Fabrication 190

7.2.1 Radical Solution Polymerization 190 7.2.2 Aqueous Emulsions 192 7.2.3 Saponification 195 7.2.4 Foaming 196

7.3 Properties 197 7.3.1 Mechanical Properties 197 7.3.2 Optical Properties 197

7.4 Applications 197 7.4.1 Blends 197 7.4.2 Heat Seal Applications 198 7.4.3 Sealing 199 7.4.4 Waxes 201 7.4.5 Hot Melt Adhesives 202 7.4.6 Cold Flow Improvers 202 7.4.7 Drug Delivery 204


8 Acrylonitrile-Butadiene-Styrene Polymers 211 8.1 Monomers 211

8.1.1 Rubbers 213 8.2 Polymerization and Fabrication 215

xii Engineering Thermoplastics: Polyolefins and Styrenics

8.2.1 Mass Polymerization 215 8.2.2 Emulsion Polymerization 218 8.2.3 Low Gloss Types 221 8.2.4 Blends 221

8.3 Properties 227 8.3.1 Mechanical Properties 227 8.3.2 Thermal Properties 228 8.3.3 Electrical Properties 229 8.3.4 Optical Properties 230 8.3.5 Surface Properties 231

8.4 Special Additives 231 8.4.1 Heat Stabilizers 232 8.4.2 Flame Retardants 232 8.4.3 Combined UV Stabilizer and Flame Retardant 234 8.4.4 Fillers 235

8.5 Applications 236 8.5.1 Foam Stops 236 8.5.2 Electroconductive Resins 236 8.5.3 Tunable Magneto Rheological Compositions . 237 8.5.4 Cement Additive 237 8.5.5 Membrane Materials 238 8.5.6 Electroless Plating 240 8.5.7 Encapsulation Shells for Phase Change Materials241 8.5.8 Hydrogen Storage 242 8.5.9 Carbon Materials 243

8.6 Suppliers and Commercial Grades 244 8.7 Safety 244 8.8 Environmental Impact and Recycling 247

8.8.1 Material Recycling 247 8.8.2 Pyrolysis 252

References 256

9 High Impact Poly(styrene) 269 9.1 Monomers 269

9.1.1 Impact Modifiers 269 9.2 Polymerization and Fabrication 270

9.2.1 Continuous Radical Polymerization 271 9.2.2 Rubbers 272

Contents xiii

9.2.3 Nanocomposites 274 9.3 Properties 275

9.3.1 Mechanical Properties 276 9.3.2 Thermal Properties 276 9.3.3 Particle Size 276

9.4 Special Additives 278 9.4.1 Flame Retardants 278

9.5 Applications 279 9.5.1 Foodservice Applications 279 9.5.2 Refrigerator Cabinets 281 9.5.3 Antistatic Compositions 282

9.6 Suppliers and Commercial Grades 283 9.7 Safety 283

9.7.1 Emissions from Processing 283 9.7.2 Emissions from Recycled Products 286 9.7.3 Accumulation in Food from Packaging . . . . 287

9.8 Environmental Impact and Recycling 288 9.8.1 Material Recycling 288 9.8.2 Feedstock Recycling 291

References 292

10 Styrene/Acrylonitrile Polymers 297 10.1 Monomers 297 10.2 Polymerization and Fabrication 297

10.2.1 Emulsion Polymerization 298 10.2.2 Intermediate Polymerization 298 10.2.3 Solution and Bulk Polymerization 298 10.2.4 Expandable Microspheres 300 10.2.5 Modification 300 10.2.6 Interfering Reactions 302

10.3 Properties 302 10.3.1 Mechanical Properties 303 10.3.2 Thermal Properties 303 10.3.3 Electrical Properties 304 10.3.4 Optical Properties 304 10.3.5 Chemical Resistance 305


xiv Engineering Thermoplastics: Polyolefins and Styrenics

10.5.1 Blends 306 10.5.2 Expandable Resins 308 10.5.3 Low Gloss Additives 308 10.5.4 Laser-inscribed Moldings 309

10.6 Suppliers and Commercial Grades 310 10.7 Environmental Impact and Recycling 310 References 312

11 Methyl methacrylate/Butadiene/Styrene Polymers 315 11.1 Monomers 315 11.2 Polymerization and Fabrication 316

11.2.1 Basic Method for Preparation 316 11.2.2 Varied Methods 318

11.3 Properties 318 11.3.1 Thermal Properties 319 11.3.2 Optical Properties 319


11.5.1 Medical Applications 320 11.5.2 Impact Modifiers 320 11.5.3 Thermoforming Applications 321 11.5.4 Aqueous Additive Systems 321 11.5.5 Prepregs 322 11.5.6 Powder Coatings 324


12 Acrylonitrile/Styrene/Acrylate Polymers 331 12.1 Monomers 331 12.2 Polymerization and Fabrication 332

12.2.1 Two Stage Preparation for Structured Latexes 333 12.2.2 Three Stage Preparation 334 12.2.3 Blends 335

12.3 Properties 336 12.3.1 Mechanical Properties 337 12.3.2 Optical Properties 338 12.3.3 Chemical Properties 338

12.4 Special Additives 338 12.4.1 Weatherability Improvers 339

Contents xv

12.4.2 Gloss Reducers 339 12.4.3 Heat Distortion Improving Agents 340

12.5 Applications 341 12.5.1 Multilayer Laminates 342 12.5.2 Roofing Material 342 12.5.3 Antimicrobial Acrylonitrile-styrene-acrylate . 343


Index 349 Tradenames 349 Acronyms 361 Chemicals 364 General Index 375

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1

Metathesis Polymers

Polymers using the ring opening metathesis polymerization (ROMP) technique were first obtained at 1960 by Eleuterio (1,2). The patents deal with the polymerization of bicyclo[2.2.1]heptene-2, i.e., nor-bornene using a molybdenum catalyst dispersed on alumina.

The polymer was found to contain double bonds in trans and cis-configuration in considerable amounts. The mechanism of polymer-ization has been described as shown in Figure 1.1.

Metal-catalyzed olefin metathesis had an enormous impact on organic synthesis in general. Extensive research on mechanistic aspects (3,4) and the development of catalysts has been performed, which culminated in the award of the Nobel Prize for Chemistry in 2005 to Chauvin, Grubbs and Schrock.

G -

Figure 1.1: Metathesis Polymerization of Norbornene and Cyclopentene

1

2 Engineering Thermoplastics: Polyolefins and Styrenics

Table 1.1: Monomers for Metathesis Polymerization Monomers References Cyclopentene 1,5-Cyclooctadiene Norbornene (1/2) l,4-Dihydro-l,4-methanonaphthalene Norbornene 2-ethylhexyl carboxylate (5) Norbornene isobornyl carboxylate (5) Norbornene phenoxyethyl carboxylate (5) Dodecylenedinorbornene dicarboxyimide (5) exo,e;ro-N,N'-Propylene-di-(norbomene-5,6-dicarboxyimide (5) 8-Methyltetracyclo[4.4.0.12.8.17.10]dodeca-3-ene (6) Dicyclopentadiene (6)

1.1 Monomers Cyclopentene is readily available as a byproduct in the ethylene production. Norbornene 2-ethylhexyl carboxylate is obtained by the Diels-Alder reaction of 2-ethylhexyl acrylate with cyclopenta-diene (5). Norbornene isobornyl carboxylate, norbornene phen-oxyethyl carboxylate, and other related monomers are synthesized according to the same route. Polymers obtained from these esters exhibit excellent properties in terms of controlling the crosslink-ing density, the associated product modulus, and the glass tran-sition temperature (Tg), thus allowing tailoring the properties of elastomers, plastics and composites. Other suitable monomers are summarized in Table 1.1 and sketched in Figure 1.2.

1.2 Polymerization and Fabrication

The monomers dealt with can be polymerized by various mecha-nisms, not only by ROMP. For example, a rapid polymerization of norbornadiene occurs using a homogeneous catalytic system consisting of nickel acetylacetonate or a nickel-phosphine complex, such as nickel bis-(tri-n-butylphosphine) dichloride (NiCl2(TBP)2) or nickel bis-(tricyclohexylphosphine) dichloride (NiCl2(TBP)2). Nickel acetylacetonate as catalyst is known to initiate rather a clas-sical vinyl polymerization (7). The classical vinyl polymerization

Metathesis Polymers 3

O ch Cyclopentene Norbornene Dicyclopentadiene

*̂ ® O 1,4-Dihydro-1,4-melhanonaphthalene 1,5-Cyclooctadiene

Figure 1.2: Monomers used for Metathesis Polymers

Figure 1.3: Difference Between Vinyl Polymerization and Ring Opening Metathesis Polymerization (7)

of cyclic monomer deserves much less attention in the literature, nevertheless there is a big variety of catalysts described (7).

By the way, the intended use of this polymer is as a solid high en-ergy fuel (8). The difference between ordinary vinyl polymerization and ring opening metathesis polymerization is shown in Figure 1.3.

1.2.1 Metathesis Reaction

The metathesis reaction consists of a movement of double bonds between different molecules, as shown in Figure 1.4. Thus, the metathesis reaction can be addressed as a transalkylideneation re-action. The cleavage of the carbon-carbon double bonds was es-tablished using isotopic labelled compounds that were subjected to ozonolysis after reaction (9).

Clearly, if the radicals R\ and R4 are connected via a carbon chain, a longer chain will be formed, resulting consecutively in the for-


R 4 \ ßl R4V ßl C=C C C

R3 R2 R3 R2

Figure 1.4: Scheme of Metathesis Reaction

Table 1.2: Types of Metathesis Reactions (10)

Term Acronym

Ring opening metatheses polymerization ROMP Living ring opening metatheses polymerization LROMP (11,12) Ring closing metathesis RCM Acyclic diene metathesis polymerization ADMET Ring opening metathesis ROM Cross-metathesis CM or XMET

mation of macromolecular structures. For this reason, this type of polymerization is also called ring opening polymerization. The polymeric structures contain double bonds in the main chain. This allows classical vulcanization processes with sulphur. Since the reaction is reversible, the metathesis process has been used to syn-thesize degradable polymers with vinyl groups in the backbone. In this way, the structure of crosslinked rubbers has been elucidated.

The mechanism of metathesis is used in several variants, either to polymerize, degrade, etc. The various reaction types are sum-marized in Table 1.2. The metathesis reaction is catalyzed by metal-carbene complexes. The mechanism, exemplified with cyclopentene is shown in Figure 1.5. In the first step, the complex reacts with a monomer to regenerate the carbon metal double bond. This double bond is able to react further with another monomer thus increasing the size of the molecule.

If the metathesis polymerization is performed in solution, the preferred solvents are méthylène chloride or chlorobenzene. Prefer-ably, the solvent is aprotic in order to avoid ionic side reactions. The molecular weight is controlled by the addition of an acyclic olefin, such as 1-butene (13).

The polymerization reaction can be quenched by the addition of alcohols, amines or carboxylic acids, such as ethanol, ferf-butyl


OH3 H CHQ H

H3C-¿ ¿ ^\ ^ H3C-¿ ¿=^Λ

OC I vCO V̂\f CO OC'IvCO CO

Figure 1.5: Initial Steps of the Metathesis Polymerization

phenol, diethylamine, acetic acid. The polymerization reaction is an equilibrium reaction. The relevant equilibria are

1. Monomer-polymer equilibrium, in more general sense, 2. Equilibrium between polymers of different chain length, 3. Ring-chain equilibrium, and 4. C/s-frans-equilibrium.

The free enthalpy of polymerization (AGp) is sufficiently negative for rings of a size of 3, 4, 8, and larger to have the equilibrium on the side of the polymer. However, for rings of a size of 5, 6, and 7 - because of the low ring tension - the free enthalpy of polymer-ization can be even positive. For example, AGa,p for the formation of the c/s-polymer of cyclohexene, AGo,p = +6.2 kjmol"1 and for frans-polymer of cyclohexene, AGo,p = +7.3 kj mol"1 (14). Howev-er, at cryogenic temperatures, AGp decreases and oligomers can be formed.

The polymer contains a fraction of high molecular linear chains and a cyclic oligomeric fraction. If initially the monomer concentra-tion is below the equilibrium value for a linear polymer, essentially no polymer is formed, but only cyclic oligomers. At higher concen-tration, both a linear polymer and a cyclic oligomer is formed.

The ratio of the amounts of c/s-linkages to irans-linkages depends on the nature of the catalyst. A tungsten or molybdenum cata-lyst, respectively, can be prepared by heating tungsten trioxide with phosphorus pentachloride in o-dichlorobenzene up to 120°C under vigorous stirring. The solution changes from colorless to deep red and a considerable amount of precipitate is left behind at the bottom of the reaction vessel. The soluble chloride is used for the further steps.


Table 1.3: Monomers for ROMP Polymerization (15)

Monomer Rate3 f]b

Cyclopentenec

Bicyclo[2.2.1]heptene-2c 5-Cyano-5-methyl-bicyclo[2.2.1]heptene-2 3,6-Methylene-l,2,3,6-tetrahydro-ris-phthalic anhy-dride

2,3-Diethoxycarbonyl-bicyclo[2.2.1]hepta-2,5-diene 1,5-Cyclooctadienec N-Phenyl-3,6-methylene-l,2,3,6-tetrahy-dro-ds-phthalimide

N-Butyl-3,6-methylene-l,2,3,6-tetrahydro-cz's-phthalimide

5,6-Dimethoxycarbonyl-bicyclo[2.2.1]heptene-2 5-(4-Quinolyl)-bicyclo[2.2.1]heptene-2 5-Acetoxy-bicyclo[2.2.1 ]heptene-2 5-Methoxymethylbicyclo[2.2.1]heptene-2 A/,N-Diethyl-bicyclo[2.2.1 ]heptene-2-carbonamide l,4-Dihydro-l,4-methanonaphthalene 5-Chloromethyl-bicyclo[2.2.1 ]heptene-2 5-(2-Pyridyl)-bicyclo[2.2.1]heptene-2 5,5-Dichloro-bicyclo[2.2.1 ]heptene-2 a Rate of polymerization/ [g g_1h_1] at 70°C except for monomers

with superscriptc b Viscosity/ [dig- 1] c Polymerized at 30°C d Solvent: 1,2-dichloroethane e Solvent: N,JV-dimethylformamide

The actual polymerization takes place in an autoclave under inert atmosphere, where the supernatant liquid of the foregoing step is placed with the dried and rectified monomer and the second cata-lyst compound, namely diethylaluminum chloride in 1,2-dichloro-ethane solution (15). The polymerization is conducted at 70°C for 60 min while stirring well. According to this recipe, a series of cyclic monomers can be polymerized. Examples are shown in Table 1.3.

Macromonomers provide an easy access to a large number of functional copolymers and controlled topologies, such as comb-like, star-like, bottle brush, and graft copolymers. These types exhibit exceptional solution or solid state properties compared to their linear homologues.

1,590 1,365 1,365

1,283 1,264 1,202

1,182

1,121 1,039

998 978 978 937 897 876 876 815

2.05d 1.88d

1.22e

0.97e

1.17e

1.98d

1.05d

1.07e

0.70e

0.81e 0.85e

0.69e 0.94e

0.78d

0.80d

0.81e

l . l l d


Initially, the polymerization of macromonomers was achieved by free radical polymerization reactions, which allowed only a limited control of the final properties. With the advent of ROMP and new free radical polymerization techniques, such as atom transfer radical polymerization (ATRP) the control of final properties became more facile (16). ATRP and ROMP techniques can be combined for the synthesis of macroinitiators (17).

Macromonomers with norbornene end groups were synthesized by living anionic polymerization. The norbornene groups were polymerized by molybdenum catalysts. A series of other ω-nor-bornenyl macromonomers were synthesized and polymerized by metathesis polymerization.

1.2.1.1 Living Ring Opening Metathesis Polymerization

Living ring opening metathesis polymerization is a special kind of ROMP. In order to approach the conditions of a living polymeriza-tion reaction, the following requirements must be fulfilled (12):

1. Fast and complete initiation, 2. Linear relationship between the degree of polymerization

and conversion, and 3. Polydispersity less than 1.5.

Thus, the catalyst must have certain special properties, to be regarded as a living ROMP catalyst.

1.2.2 Catalysts

Numerous catalyst systems have been developed. Most common catalysts are based on tungsten of molybdenum. Transition metals ranging from group IV to group VIII have been found to be suitable. The catalysts are commonly classified as given in Table 1.4.

The half-life times of the polymerization reaction can be adjusted from a few seconds to several days. Typical for such catalysts is the metalcarbene bond, as shown in Figure 1.5. In varieties of the catalytic principle of the metalcarbene bond, this bond is not initially present, but may be formed by a co-catalyst or by some reactions with the monomer itself.


Table 1.4: Classification of Catalysts (18) Catalyst Type Initiators with metal alkyl co-catalysts Initiators with alkylidene or metallacyclobutanes of early transition metals

Group VIII initiators without metal alkyl co-catalysts Group VIII alkylidenes

Table 1.5: Monomer Catalyst Systems (14) Monomer Catalyst T /°Ca Property1" Cyclopentene WCl6/(CH2=CHCH2)4Si -10 high eis Cyclopentene WC16/CH3-CH2A1C12 +20 high trans CIMXHs C6H5C=W(CO)4Br M„ = 5.9 k Dalton a Temperature of polymerization b Property of polymer

Examples for catalysts are listed Table 1.5 and shown in Figure 1.6. For the metathesis polymerization of acetylene related compounds,

catalysts with a metal carbyne bond have been introduced, such as

C6H5C = W(CO)4Br.

Molybdenum-based catalysts are highly active initiators, how-ever, monomers with functionalities with acid hydrogen, such as alcohols, acids, or thiols jeopardize the activity. In contrast, ruthe-nium-based systems exhibit a higher stability towards these func-tionalities (19). An example for a molybdenum-based catalyst is (20) MoOCl2(t-BuO)2, where t-BuO is the terf-butyl oxide radical. The complex can be prepared by reacting M0OCI4 with potassium tert-butoxide, i.e., the potassium salt of ierf-butanol.

Ruthenium and osmium carbene complexes possess metal cen-ters that are formally in the +2 oxidation state, have an electron count of 16 and are penta-coordinated. Ruthenium complexes ex-hibit a higher catalytic activity when an imidazole carbene ligand is coordinated to the ruthenium metal center (21).

The polymerization of cyclooctene shows a pronounced depen-dence of the N-heterocyclic carbene ligand, due to steric effects.


α P(Cy)3 'RU=

C K I

R—N N—R

(II)

OH3 '~'3*-/

C/H3 '~'3^-/

Ck Ru=

.Ph

C K l PBu3

(III)

Figure 1.6: Metathesis Catalysts (22): Phenylmethylene-bis-(tricyclohexyl-phosphine) ruthenium dichloride (I), (IMesH2)(PCy3)(Cl)2Ru=CHPh (III)

These ruthenium complexes are also active catalysts for ring-closing metathesis reactions in high yields.

Ruthenium catalysts, coordinated with an N-heterocyclic carbene allowed for the ROMP of low-strain cyclopentene and substituted cyclopentenes (10,23). Suitable ruthenium and osmium carbene compounds may be synthesized using diazo compounds, by neu-tral electron donor ligand exchange, by cross metathesis, using ac-etylene, cumulated olefins, and in an one-pot method using diazo compounds and neutral electron donors (24). The route via diazo compounds is shown in Figure 1.7.

Since the ruthenium and osmium carbene compounds of the type shown in Figure 1.7 are stable in the presence of a variety of func-tional groups, the olefins involved in the polymerization reactions may optionally be substituted with various functional groups.

The synthesis of a ruthenium catalyst in a one step procedure is shown in Figure 1.8. A dimer complex of cymene, i.e., 4-iso-propyltoluene) and RuCl2 is reacted under inert atmosphere with tricyclohexylphosphine and 3,3-diphenylcyclopropene in benzene


PPh3 M PPh3 H

^Ru—PPh3 + A ►- ^Ru=C CK^l 3 R--K,, CKl NR

PPh, H H pph3 H

'3

Figure 1.7: Synthesis of Ruthenium Carbene Compounds via Diazo Com-pounds (24)

solution under reflux at 83-85°C for 6 h (25). The catalyst Cl2Ru(PCy3)2(=CHCH=CPh2), cf., Figure 1.8, is ob-

tained in a yield of 88%. In the same way, catalysts, where the metal atom is in a ring, can be synthesized. This type of catalysts is suit-able for the synthesis of cyclic polymers (26). The synthesis route is shown in Figure 1.9.

The preparation of the catalyst starts with the synthesis of 1-mes-ityl-3-(7-octene)-imidazole bromide. This compound is prepared by condensing mesityl imidazole with 8-bromooctene. The resulting salt is deprotonated with (TMS)2NK, where TMS is the tetrameth-ylsilyl radical. This step is performed in tetrahydrofuran at -30°C for 30 min. To this product a solution of the ruthenium complex (PCy3)2Cl2Ru=CHPh is added at 0°C. Bringing the solution slowly to room temperature, after 1 h the ligand displacement was deter-mined to be complete. Afterwards, the reaction mixture is then diluted with n-pentane and heated to reflux for 2 h to induce in-tramolecular cyclization.

The ruthenium catalyst can be used to catalyze the synthesis of a cyclic poly(octenamer). The catalyst is added to cis-cyclooctene in CH2CI2 solution at 45° C. The intermediate macrocyclic complex un-dergoes an intramolecular chain transfer to yield the cyclic polymer and regenerate the catalyst.

In this way, cyclic polymers with number-average molecular weights M„ up to 1200 k Dal ton can be prepared by varying the ration of catalyst to monomer or the initial monomer concentration.

However, with initial monomer concentrations of less than 0.2 moll - 1 , only low molecular weight cyclic oligomers are obtained. The polydispersity index Mw/Mn of the resulting polymers is ap-proximately 2.

In the case of cycloolefin monomers with a strained double bond,


CI—Ru Cl( "CI +

Ru-CI

Figure 1.8: Synthesis of a Ruthenium Catalyst (25)


pzKJ+^

N N ^__^

' x'i

Figure 1.9: Catalyst for Macrocyclic Polymers

such as norbornene, the ring opened product is thermodynamically favored. Therefore, it is not necessary for the catalyst to bear a met-alcarbene moiety in its structure to initiate the ROMP. Any complex capable of initiating metalcarbene formation in situ should perform equally well as a catalyst for the ROMP. For instance, it is well known that RuC^ x 3H2O can accomplish the ROMP of norbornene quite effortlessly, even though there is no carbene present in the cat-alyst. It is suspected that the reaction involves as a first step, when the metal halide reacts with the monomer, the formation of a metal-carbene moiety that is responsible for the subsequent propagation reaction (20).

Hydrates of RUCI3, IrCl3, and OsCb are suitable catalysts for the ROMP of norbornene in aqueous and alcoholic solvents. Ruthe-nium trichloride hydrate is used for the industrial production of poly(norbornene). These hydrates act for the ROMP of norbornene and norbornene derivatives in pure water through an emulsion pro-cess (18).

Olefin metathesis catalysts based on ruthenium have been shown to exhibit a quite good tolerance to a variety of functional groups. The ring opening metathesis polymerization of strained, cyclic ole-fins initiated by group VIII salts and coordination complexes in aque-

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