syndiotactic polystyrene synthesis characterization processing and applications

Cover image: Scanning electron micrographs of syndiotactic polystyrene prepared by a powder bed polymerization process showing the typical “caulifl ower” structure of the powder SEM: Dow

POLYSTYRENE

SYNTHESIS, CHARACTERIZATION, PROCESSING, AND APPLICATIONS

Edited by

Jürgen Schellenberg

R&D Dow Central Germany

Dow Olefi nverbund GmbH, Schkopau, Germany

A John Wiley & Sons, Inc., Publication

SYNDIOTACTIC POLYSTYRENE

New supramolecular structure of tactic polystyrene showing a “bird’s-nest-like” structure, obtained from a cyclohexanol solution by thermally induced phase separation (scanning electron microscope image by M van Heeringen, Dow Terneuzen) (Van Heeringen, M., Vastenhout, B., Koopmans,

syndio-R., Aerts, L e-Polymers [2005], no 048.)

POLYSTYRENE

SYNTHESIS, CHARACTERIZATION, PROCESSING, AND APPLICATIONS

Edited by

Jürgen Schellenberg

R&D Dow Central Germany

Dow Olefi nverbund GmbH, Schkopau, Germany

A John Wiley & Sons, Inc., Publication

Cover image: Scanning electron micrographs of syndiotactic polystyrene prepared by a powder bed polymerization process showing the typical “caulifl ower” structure of the powder (SEM: Dow Central Germany).

Copyright © 2010 by John Wiley & Sons, Inc All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.

Published simultaneously in Canada.

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Library of Congress Cataloging-in-Publication Data:

Dedicated to Prof Dr habil Joachim Ulbricht,

a Pioneer in the Fields of Polymer Chemistry and Coordination Polymerization

vii

PREFACE xvii CONTRIBUTORS xxi

Norio Tomotsu, Thomas H Newman, Mizutomo Takeuchi,

Richard Campbell Jr., and Jürgen Schellenberg

References 29

viii CONTENTS

Norio Tomotsu, Hiroshi Maezawa, and Thomas H Newman

References 58

5 Copolymerization of Ethylene with Styrene: Design of Effi cient

Kotohiro Nomura

5.2 Ethylene/Styrene Copolymers: Microstructures, Thermal

5.3 Ethylene/Styrene Copolymerization Using Transition Metal

Radicals 102

6.5.1 Synthesis of Tbf Titanium Monophenoxide

Complexes 1076.6 Dynamic and Polymerization Behavior of

x CONTENTS

8 Syndiospecifi c Styrene Polymerization with Heterogenized

Kyu Yong Choi

8.2 Kinetics of Syndiospecifi c Polymerization with

8.2.1 Kinetic Profi les of Heterogeneous SPS

Polymerization 1418.2.2 Liquid Slurry Polymerization with Heterogenized

8.2.4 Molecular Weight Distribution of SPS with

8.3.1 Physical Transitions of Reaction Mixture During

Polymerization 1498.3.2 Effect of Reaction Conditions on Polymer

9.2.3 Morphology Development in the Presence of

Solvents 163

9.3.3 Lamellar and Spherulitic Morphology of the

CONTENTS xi

9.5.1 Thermodynamic and Kinetics of Crystallization 177

9.6.1 Equilibrium Melting Temperature of α and β

Crystals 180

9.7 Structure and Properties of the Crystallized Samples 183

9.7.2 Relation between Morphology Structure,

References 186

10 Preparation, Structure, Properties, and Applications of Co-Crystals

Gaetano Guerra, Alexandra Romina Albunia, and Concetta D’Aniello

xii CONTENTS

11.4 Analyses of Spherulitic Growth Rate G 248

References 250

PART IV COMMERCIAL PROCESSES FOR MANUFACTURING

Masao Aida, David Habermann, Hans-Joachim Leder, and

12.4.2 Continuous Fluidized Bed Reactor Process 25812.4.3 Continuous Self-Cleaning Reactor Process 258

Tomoaki Takebe, Komei Yamasaki, Keisuke Funaki, and Michael Malanga

13.4 Orientation of SPS and Properties of Oriented SPS 281

13.4.2 Properties of Biaxially Oriented SPS (BoSPS) 282

David Bank, Kevin Nichols, Harold Fowler, Jason Reese, and

14.3.5 Injection Mold Melt Delivery System (Runners

14.3.7 Injection Molding Cooling Cycle and

Crystallinity 304

xiv CONTENTS

Tom Fiola, Akihiko Okada, Masami Mihara, and Kevin Nichols

15.3 Connectors for Automotive and Electronic Applications 329

References 337

Kevin Nichols, Akihiko Okada, and Hiroki Fukui

16.2.4 SPS/Nylon Blend Compositions Described in

16.3.1 Mechanical Properties of SPS/Nylon Blends 340

16.3.3 Moisture Absorption and Moisture Growth of

16.3.4 Dimensional Stability of SPS/Nylon Blends 346

16.3.6 Environmental Stress Crack Resistance of

16.4.1 SPS/Nylon Blend Under-the-hood Automotive

Connectors 349

References 355

Tomoaki Takebe, Komei Yamasaki, Akihiko Okada, and

Takuma Aoyama

CONTENTS xv

References 370

Tomoaki Takebe, Akihiko Okada, and Nobuyuki Sato

18.2.1 SAXS Profi les of HISPS in the Crystalline State 37418.2.2 Effect of Nucleators on Lamellar Orientation

18.3.1 Structural Analyses Using SAXS Technique 37718.3.2 Crystallization Kinetics of SPS/PPO Blends 37818.3.3 Infl uence of Blending PPO with Different

Molecular Weights on the Morphology of HISPS 380

18.4.2 Evaluation of Domain Size and Interfacial

Thickness 388References 393

PART VI POLYMERS BASED ON SYNDIOTACTIC

POLYSTYRENES 395

19 Functionalization and Block/Graft Reactions of Syndiotactic

Polystyrene Using Borane Comonomers and Chain Transfer

Agents 397

T C Mike Chung

19.2.1 Copolymerization of Styrene and B-styrene 398

19.3 Functionalization of SPS via Borane Chain Transfer

Agents 40919.3.1 SPS Containing a Terminal Functional Group 410

xvi CONTENTS

References 415

O Ok Park and Mun Ho Kim

20.5.1 Effect of Alkyl Chain Aggregation in

Organoclay—Bilayer versus Monolayer Arrangement 42320.5.2 Improvement in the Thermal Stability of

xvii

In 1953, Karl Ziegler discovered that selected transition metal compounds can

be activated by aluminum alkyls and can be used as organometallic catalysts

to polymerize ethylene One year later, Giulio Natta synthesized further reoregular polymers such as polypropylene Both scientists were awarded the Nobel Prize for Chemistry in 1963 Their fundamental work resulted in a signifi cant increase in research intensity and in an immediate commercializa-tion of these polymers

After these discoveries, one of the most important achievements in dination polymerization chemistry has been the introduction of methylalumi-noxanes as a new class of aluminum alkyl activators by Sinn and Kaminsky at the end of the 1970s, prepared by controlled hydrolysis of methylaluminum alkyls Such cocatalysts together with metallocene compounds led to an out-standing enhancement of polymerization activity and effi ciency and to a con-siderable improvement of the molecular uniformity of the polymers obtained Thus, methylaluminoxanes together with metallocene catalysts allowed the synthesis of highly stereoregular and stereoblock polypropylenes, ethylene copolymers with a higher content of comonomer or with higherα - olefi ns and other monomers, cycloolefi n polymers of high crystallinity and their copoly-mers, as well as polyethylenes with improved rheological properties by con-trolled long - chain branching

As a result of these developments, syndiotactic polystyrene (SPS) was pared by activated titanium compounds as polymerization catalysts The fi rst SPS was synthesized by Ishihara et al in 1985 using a homogeneous organo-metallic catalytic system based on titanium compounds and methylaluminox-ane as cocatalyst The polystyrene initially obtained was a polymer with a

pre-2 - butanone - insoluble content as a measure of the syndiotacticity of 98 wt%, a weight - average molecular weight of 82,000 g/mol, and a melting temperature

of about 270 ° C, 40 ° C higher than that of the isotactic polystyrene known since 1955

However, the most important advantage of this SPS in comparison to the isotactic polymer is the much higher crystallization rate of the polymer melt, comparable to that of polyethylene This high crystallization rate enabled an advantageous processing of the polymer by extrusion and injection molding techniques After the development of commercially viable transition metal catalysts with high polymerization activity, this new, highly stereoregular polymer was successfully commercialized in 1999 Further desirable properties

xviii PREFACE

of this polymer are high heat resistance based on the high melting temperature

of 270 ° C; excellent chemical resistance to reagents including acids, bases, oils, water, and steam; good electrical properties as insulating materials with a low dielectric constant and a low dissipation factor; low polymer density of 1.05 g/

cm3 with nearly equivalent densities in crystalline and amorphous regions; excellent processing characteristics at a very low melt viscosity; outstanding dimensional stability; and low moisture absorption The less desirable brittle-ness of SPS has been overcome by reinforcement with glass fi bers, altogether leading to an advantageous new polymer in the class of semicrystalline engi-neering thermoplastics

This book comprehensively covers all aspects of SPS, from the synthesis of this new polymer by coordination polymerization to the characterization of structure, properties, and behavior of the neat material as well as of plastic materials, including the different processing opportunities of such materials,

to the widely diversifi ed applications of polymers and blends, also considering SPS - based polymers

The Introduction gives a historical overview of SPS from the fi rst discovery through developmental stages to the full commercialization of this polymer based on an inexpensive monomer (Chapter 1 ) Because the transition metal catalysts for the coordination polymerization of styrene are of high impor-tance for the properties of the polymers, these catalysts are comprehensively covered in the section on the preparation of SPS

After an overview of the transition metal catalysts for SPS, primarily half metallocenes of group 4, in Chapter 2 , details on cocatalysts for SPS are given

-in Chapter 3 followed by an overview on mechanism and k-inetics of the diospecifi c styrene polymerization, including active site formation, in Chapter

4 The design of effi cient transition metal complex catalysts for the merization of ethylene with styrene is described in Chapter 5 The subsequent chapters include some selected groups of special transition metal catalysts,

copoly-such as novel tetrabenzo[ a,c,g,i ]fl uorenyl - based titanium catalysts as

derivatives of the highly effi cient hydrogenated fl uorenyl catalysts (Chapter 6 ), rare earth metal complexes (Chapter 7 ), and heterogenized transition metal catalysts (Chapter 8 )

In the section on structure and fundamental properties of SPS, Chapter 9 summarizes the polymorphic behavior of this polymer, the structure of the different forms, and the crystallization and melting behavior Chapter 10 describes co - crystals and nanoporous crystalline phases of SPS regarding preparation, structure, properties, and new interesting applications, for example, molecular sensors The section concludes with Chapter 11 on selected topics of crystallization thermodynamics and kinetics of SPS

The next section on commercial processes for manufacturing of SPS describes the process for the production of this polymer in more detail (Chapter 12 )

The comprehensive section on properties, processing, and application of SPS discusses the rheological, mechanical, and other properties of this polymer

PREFACE xix

(Chapter 13 ) and continues with melt processing, including injection molding, extrusion, fi lms, and fi bers (Chapter 14 ) Chapter 15 goes on to describe appli-cations of SPS polymers themselves, followed by a discussion of blends with polyamides in Chapter 16 and with conventional polystyrenes in Chapter 17 Compatibilizers for impact - modifi ed SPS are covered in Chapter 18

The last section on polymers based on SPS includes the different ties for functionalization and modifi cation of SPS in Chapter 19 and nanocom-posites based on SPS described in Chapter 20

The intent of this book is to provide the reader with comprehensive edge about SPS based on a historical overview on this polymer, not only by summarizing the fundamentals of this stereoregular polymer but also by describing the latest new developments in this area However, this book cannot be exhaustive because of the very broad interest this polymer has received in academic research as well as in industry

Gratefully acknowledged is the excellent work done by all authors, as well

as the successful collaboration with the publisher, John Wiley & Sons, Inc., at all stages of the preparation and publishing of this book

J ü rgen S chellenberg

March 2009

xxi

Masao Aida , Process Development Center, Idemitsu Kosan Co., Ltd., Chiba,

Japan

Alexandra Romina Albunia , Dipartimento di Chimica, University of Salerno,

Fisciano (SA), Italy

Corporation, Southfi eld, MI, USA

David Bank , Dow Automotive R & D, The Dow Chemical Company, Midland,

MI, USA

Klaus Beckerle , RWTH Aachen University, Aachen, Germany

Ossietzky University, Oldenburg, Germany

Midland, MI, USA

Midland, MI, USA

University of Maryland, College Park, MD, USA

T C Mike Chung , Department of Materials Science and Engineering, The

Pennsylvania State University, University Park, PA, USA

Concetta D ’ Aniello , Dipartimento di Chimica, University of Salerno, Fisciano

(SA), Italy

Tom Fiola , Xarec and SPS Products, Idemitsu Chemicals USA Corporation,

Southfi eld, MI, USA

Harold Fowler , Ventures & Business Development, The Dow Chemical

Company, Midland, MI, USA

David Habermann , Information Systems Management, The Dow Chemical

Company, Midland, MI, USA

Osamu Isogai , Kukankoubou Co., Ltd., Chiba, Japan

Shigeo Iwasaki , Technology and Engineering Department, Idemitsu Kosan

Co., Ltd., Chiba, Japan

Korea Advanced Institute of Science and Technology, Daejeon, Korea

Masahiko Kuramoto , Chemicals Development Center, Idemitsu Kosan Co.,

Ltd., Chiba, Japan

Hans - Joachim Leder , R & D Dow Central Germany, Dow Olefi nverbund

GmbH, Schkopau, Germany

Hiroshi Maezawa , Technology and Engineering Department, Idemitsu Kosan

Co., Ltd., Tokyo, Japan

Michael Malanga , R & D Advanced Technologies, The Dow Chemical

Company, Auburn Hills, MI, USA

Masami Mihara , Idemitsu Kosan Co., Ltd., Chiba, Japan

Thomas H Newman , Science Division, Delta College, University Center, MI,

USA

Kevin Nichols , R & D Dow Building Solutions, The Dow Chemical Company,

Midland, MI, USA

Kotohiro Nomura , Graduate School of Materials Science, Nara Institute of

Science and Technology, Nara, Japan

Akihiko Okada , Engineering Plastics Department, Idemitsu Kosan Co., Ltd.,

Tokyo, Japan

CONTRIBUTORS xxiii

Jun Okuda , RWTH Aachen University, Aachen, Germany

O Ok Park , Department of Chemical and Biomolecular Engineering, Korea

Advanced Institute of Science and Technology, Daejeon, Korea

Jason Reese , Dow Automotive R & D, The Dow Chemical Company, Midland,

Inorganic Chemistry, Stratingh Institute for Chemistry, Groningen, the Netherlands

Andrea Sorrentino , Chemical and Food Engineering Department, University

of Salerno, Fisciano, Italy

Tomoaki Takebe , Chemicals Development Center, Idemitsu Kosan Co., Ltd.,

Chiba, Japan

Mizutomo Takeuchi , Research & Development Department, Idemitsu Kosan

Co., Ltd., Tokyo, Japan

Norio Tomotsu , Advanced Technology Research Laboratories, Idemitsu

Kosan Co., Ltd., Chiba, Japan

Vittoria Vittoria , Chemical and Food Engineering Department, University of

Salerno, Fisciano, Italy

Takeshi Yamada , Performance Materials Laboratories, Idemitsu Kosan Co.,

Ltd., Chiba, Japan

Komei Yamasaki , Polymer Development Center, Idemitsu Kosan Co., Ltd.,

Chiba, Japan

About the Editor

xxv

JÜRGEN SCHELLENBERG

J ü rgen Schellenberg is a specialist in polymer research with broad interests in polystyrene and styrenic polymers He was born in 1953 in Sangerhausen/Germany, studied chemistry at the Technical University “ Carl Schorlemmer ” Leuna - Merseburg, and obtained a PhD in polymer science with a thesis on the polymerization of vinyl chloride with metal acetylacetonates J ü rgen began his career in the polystyrene department of the plastics R & D division of the Chemische Werke Buna in Schkopau in 1979 There he has worked on general purpose polystyrenes, high - impact polystyrenes, styrene - acrylonitrile copoly-mers, acrylonitrile - styrene - butadiene terpolymers, special purpose styrenic polymers such as toner resins, and on polyethylene and polyethylene blends After a research stay at the Dow Chemical Company, Midland, MI, USA in 1997/1998, he continued to work on syndiotactic polystyrene (SPS) research

at Dow Central Germany/Schkopau accompanied by the start - up and tion of the fi rst commercial SPS plant worldwide, and later on worked on polypropylene and expandable polystyrene R & D too J ü rgen holds more than

opera-70 patents and has published over 47 scientifi c papers including reviews

PART I

Syndiotactic Polystyrene, Edited by Jürgen Schellenberg

Copyright © 2010 John Wiley & Sons, Inc.

Historical Overview and

The polymerization of styrene monomer has been known for over 100 years and, for about 60 years, has been one of the most important polymeric materi-als in the world The commercial success of atactic polystyrene is and has been based on many factors including its low cost, high clarity, good electrical properties, ability to be foamed, and its ease of polymerization It is, of course,

a completely amorphous polymer in the atactic confi guration and it has a glass transition temperature (Tg ) of about 100 ° C above which it is easily formed into useful objects This glass transition temperature is also one of its limita-tions in a practical sense since it cannot be used in applications above this temperature This polymer was only known in the atactic confi guration up until the 1950s when the use of heterogeneous coordination catalysts yielded polystyrene in the isotactic confi guration

The discovery of isotactic polystyrene (IPS) gave a new dimension to this material since it now could crystallize and provide a melting point (Tm) of around 250 ° C Although it still has a Tg of 100 ° C, the material will maintain its shape and may be used for many applications above this Tg and below the Tm IPS has been the subject of several intense efforts for commercializa-tion Ultimately it has been unsuccessful for one primary reason that being the rate at which the polymer will crystallize is too slow under normal forming

CHAPTER 1

4 HISTORICAL OVERVIEW AND COMMERCIALIZATION OF SYNDIOTACTIC POLYSTYRENE

processes This makes it very diffi cult to use in injection molding or extrusion processes where the crystalline properties do not develop at a rate fast enough for practical use The use of nucleating aids can increase the overall apparent rate of crystallization but not enough to overcome the relatively slow ability

of IPS segments to move into its inherent helical crystal structures

Many people speculated on the possibility of creating a polystyrene cule where the monomer units were all confi gured in a syndiotactic confi gura-tion However, this polymerization had never been successfully reported, leaving many to speculate that the monomer could never be confi gured in this manner In 1985, researchers at Idemitsu Kosan Central Research Laboratory were experimenting with the polymerization of styrene monomer using some

mole-of the recently discovered soluble coordination catalysts developed at the time using methylaluminoxane (MAO) as a counterion for titanium - based catalysts These catalysts were recently developed and were being used in olefi n polym-erizations (primarily ethylene and propylene) with claims of high reactivity What they discovered was that styrene monomer was polymerized by these types of catalysts but that the resulting polymer had a melting point of about

273 ° C, which was well above that of the known isotactic structure Tm of

250 ° C Upon further analysis, the backbone structure of this form of rene was found to be syndiotactic in confi guration, and for the fi rst time, this polymer was reported and briefl y described in a paper at a meeting of the Japanese Polymer Society in August of 1986 In that paper, the structure and basic properties were reported but not the method of polymerization or the catalyst used The report by Ishihara et al described for the fi rst time a new polymer from styrene monomer What caught the interest of many people was that SPS, unlike IPS, would crystallize to greater than 50% at a rate that made

polysty-it potentially practical and useful In addpolysty-ition, polysty-it had a melting point some

20 ° C greater than the IPS form This was a true discovery because Idemitsu Kosan Co., Ltd (IKC) had created a new polymer from an existing monomer Styrene monomer is manufactured at a rate of hundreds of millions of pounds each year around the world and is done so at a relatively low cost In a very real sense, the world was introduced to “ a new trick by an old dog ”

With the publication of this report by IKC researchers on the discovery of SPS, a fl urry of activity was set in motion in several laboratories around the world in an effort to fi nd the catalysts used In a coincidence of timing, researchers at The Dow Chemical Company (TDCC) had been investigating MAO counterions for polyethylene catalyst research Researchers there also had a renewed interest in IPS based on the ability to produce very high purity styrene monomer for anionic polymerization at a large commercial scale By December of 1986, Dow had been able to independently replicate the IKC discovery At that time, Dow was the largest commercial manufacturer of both styrene monomer and atactic polystyrene in the world, and a decision was made to pursue research and development of this new polymer At the same time, an intense research and development effort was in progress at Idemitsu and this had in fact already been ongoing for almost 2 years

EARLY YEARS OF DEVELOPMENT (1985–1989) 5

In 1988, unbeknownst to the rest of the world, Idemitsu and Dow entered into

a joint development agreement to facilitate the more rapid commercial duction of SPS Idemitsu had already applied for many patents around the world including basic composition of matter for SPS, the polymerization process, the catalysts, and many of the applications for this new material Dow had also submitted patent applications in many of the same areas, but these were generally predated by the IKC patent applications Dow had, however, endeavored to scale up the polymerization process and was already producing SPS at the scale of several hundred pounds per batch in a 500 - gal pilot plant reactor Based on the strengths, interests, and positions of both companies, an agreement was reached to share research and development results in a com-bined effort to accelerate this development This agreement included the sharing of all jointly developed future intellectual properties At the same time, a commercial agreement was put in place to allow both companies to share the value created Dow would have an exclusive license from Idemitsu

intro-on all the discovery patents for SPS that predated the agreement

The excitement at both companies revolved around the fact that this was

a new semicrystalline polymer with a melting point that made it competitive

in that regard with polyethylene terephthalate (PET), polybutylene phthalate (PBT), nylon 6 and 6,6, poly phenylenesulfi de (PPS), and even liquid crystalline polymers (LCP) while at the same time bringing the chemical resistance and dielectric properties of polystyrene Because the crystallization rate was relatively high, it could be injection molded and could still develop high crystallinity directly out of the molds It was quickly realized that these apparent crystallization rates could be enhanced with the use of added nucle-ating agents With glass fi ber, rubber modifi cation, and ignition resistance additives, it was anticipated that SPS would become an alternative engineering plastic with its own advantages

At the same time, early work in fi lm and fi ber extrusion showed that SPS could undergo strain induced crystallization with good oriented strength and modulus This opened up the prospects of applications in those markets as well Clear fi lms were possible if the crystalline phase was kept small enough not to scatter light

The key commercial prospects stemmed from the combination of

• high heat resistance,

• good chemical and electrical properties,

• some unique optical properties as a fi lm,

• ease of formability, and

• a low cost, available monomer as the only raw material

If the catalyst and polymerization process could be developed in such a way that the manufacturing costs were kept down, it was anticipated that SPS could

6 HISTORICAL OVERVIEW AND COMMERCIALIZATION OF SYNDIOTACTIC POLYSTYRENE

take its place in the plastics market rapidly as a new engineering plastic material

The initial catalysts used in the discovery of SPS involved the use of MAO made by the careful reaction of water and trimethyl aluminum as a counterion and cyclopentadienyl titanium trichloride as the active site This proved to be

a very effective catalyst system for coordinating and inserting the monomer

in a syndiotactic confi guration but was relatively ineffi cient in terms of yield This would leave a large amount of alumina and titanium oxide in the fi nal product that needed to be removed (deashed) to purify the polymer Titanium alkoxides and alkyls were also found to be effective and yields could be improved but still left enough residual ash in the polymer that it required a deashing purifi cation step This deashing was generally accomplished by washing the powder from polymer with aqueous caustic to dissolve out the alumina and then with repeated water extraction to remove the caustic resi-dues prior to drying

Although small ampoule polymerizations could take advantage of the improved kinetics afforded by carrying out the conversion in 100% styrene monomer, it became quickly apparent that this is a diffi cult system to scale

up The SPS polymer will quickly precipitate from the monomer as it lizes and after 5% – 10% conversion, it becomes a gelled mass that will solidify

crystal-to a plug if left crystal-to continue crystal-to convert The fact that the monomer still swells the polymer creates a sticky and diffi cult to agitate mass that overwhelms most reactor agitators For these reasons, the fi rst larger - scale polymerizations were conducted as slurry polymerizations using a long - chain alkyl solvent such as isooctane In this process, the polymer precipitates as fi ne particles (being very insoluble in the alkane) and can readily be agitated and pumped out of reac-tors after completion of polymerization as a slurry of SPS particles in the nonsolvent The slurry polymerization also afforded a very good means to control and remove the heat of polymerization by vaporization and condensa-tion of the cooled solvent back into the reactor

Dow used this process to make the fi rst 2000 lbs of SPS in multipurpose slurry reactor pilot plants The SPS needed to be fi ltered from the alkane, dried, and then deashed with aqueous base and water extraction and then further devolatilized to produce a pure SPS homopolymer

Idemitsu and Dow together explored a number of alternative process technologies for the SPS polymerization The kinetics of the catalysts being developed really required that one develop a process where the relative local concentration of monomer was nearly 100% This would allow for the high yields per unit of catalyst needed to eliminate the residual catalyst removal steps, to simplify the process, and to reduce cost The problems with these systems were that the heat of polymerization needed to be controlled to obtain the molecular weights and molecular weight distributions desired in the

INTENSE DEVELOPMENT YEARS (1989–1996) 7

product and that the polymer would inevitably foul agitator blades and reactor walls as it progressed through the conversion curve in batch systems

In the late 1980s and early 1990s, the two companies were running pilot plant facilities with some form of reactors that had continuously wiped walls and agitator blades In one form, these were extruder - like reactors that only carried out the polymerization through the fi rst 10% – 20% of the total conver-sion and then fed a monomer - swollen powder into a larger agitated reactor

to complete the conversion and to deal with the remaining heat evolution through the reactor walls These systems worked well and allowed for the required market development quantities with millions of pounds produced over several years This process, however, still suffered from diffi culties of heat removal in the fi rst reactor, and scale - up required high capital costs because

of the expensive extruder prereactor

Styrene monomer purifi cation and the effects of trace impurities on catalyst deactivation were also an important part of the early development of the process technology for SPS Much of the technology for oxygen and water removal to less than 1 ppm was leveraged from years of research and develop-ment on anionic polystyrene These impurities and the removal of them on an industrial scale were well known In addition to those obvious impurities for air/water sensitive catalysts, there are a number of unsaturated impurities and oxidation impurities (oxides, aldehydes, and ketones) that can form in the manufacture and storage of styrene monomer and can have a detrimental effect on the soluble coordination catalysts used for SPS polymerization Dow and Idemitsu isolated and identifi ed the effects of two key impurities, indene and phenyl acetylene in the monomer A number of effective treatments were put in place to reduce these to very low levels Improvements in yield and molecular weight control were realized through the total purifi cation of the monomer and any solvents used This was an important part of the process development for a commercially viable manufacturing plant

By 1993, it was apparent that a reduction in the capital and operating cost and an improvement in plant reliability and uptime would require modifi ca-tion of the polymerization reactor systems from what was operating in the pilot facilities at both Idemitsu and Dow In fact, what was required was an entirely new to the world polymerization process specifi cally designed to the requirements and characteristics of the SPS polymerization

SPS polymerization is unique and therefore requires a new polymerization process The polymer is insoluble in the monomer and will precipitate at very low conversion (less than 1% – 2%) The kinetics of polymerization at the temperatures that the catalysts are stable and the desired molecular weights can be achieved are highly favored in 100% concentration (pure monomer) Furthermore, the polymer is not very soluble in any suitable polymerization solvents below 110 ° C These limitations make solution polymerization imprac-tical on a commercial scale An additional restraint is that the polymerization must occur in the liquid phase No vapor - phase activity has been shown for styrene with these catalyst systems At any rate, styrene monomer would be very diffi cult and expensive to keep in the vapor form at these low tempera-

8 HISTORICAL OVERVIEW AND COMMERCIALIZATION OF SYNDIOTACTIC POLYSTYRENE

tures, requiring very high vacuum levels Batch polymerization is possible, but because of the heat of polymerization and the fact that the polymer forms the very “ sticky ” gel phase described previously, continuously wiped agitator and wall reactors are required Batch or bulk polymerization processes of this sort are also limited by heat removal capabilities Styrene monomer polymerizes very exothermically with a heat evolution of 17.8 kcal/mole Controlling this heat throughout the reacting mass is essential to making the molecular weight desired and maintaining catalyst activity Polymerization temperature must be kept at∼ 50 – 80 ° C depending on the desired molecular weight

Emulsion and suspension polymerization systems are not practical due to the need to completely exclude water Although a suspension is possible in a

fl uorinated nonsolvent for styrene, the cost of such solvents and the purifi tion of recycle streams again make it economically impractical on a commer-cial scale

ca-The breakthrough in process thinking came by considering a fl uidized powder bed polymerization reaction system where the average conversion in the reactor was kept at a steady - state high level This required a mechanical

fl uidization of the reacting powder mass and a continuous addition of monomer and catalyst into the reactor with continuous removal of polymer powder out the bottom of the reactor In addition, one can control and remove the heat

of polymerization through the use of a low - boiling nonreactive solvent tinuously added to the reacting powder mass, vaporized, externally condensed, and recycled to the reactor One further requirement of this kind of polymer-ization process is that in some way, new particles of polymer powder must be produced in the reactor or continuously added as “ seed ” to maintain a steady state of surface area for the polymerization Process research uncovered that this seeding can be accomplished through the action of friction on particles and interparticle collisions and does not require additional seeding once the reaction is under way

In the years between 1993 and 1995, Idemitsu and Dow process engineers and chemists worked together to modify and to perfect this new polymeriza-tion process, which became the basis for the design of the future manufactur-ing plants This was another historically important milestone for SPS commercialization No other polymer in the world is manufactured in a process quite the same as this, and this development allowed for a cost - effective process to be scaled up to commercial - scale plants

A closely analogous system is the vapor - phase fl uidized beds used for propylene (PP) manufacturing, but in that case, the monomer can be kept in the vapor phase and does not need to be added as a liquid This also allows one

poly-to use the propylene monomer vapor as a means poly-to remove the heat of polymeri zation PP also requires the addition of “ seed ” heterogeneous catalyst particles

Another close analogy is the precipitation mass polymerization system for polyvinyl chloride (PVC) In that case, the polymer does precipitate from the monomer, but it does not go through a self - adhering “ sticky ” stage This allows

INTENSE DEVELOPMENT YEARS (1989–1996) 9

for seed particles to be generated outside the main reactor and then to be added along with more monomers and initiators with minimized reactor fouling In the case of PVC, higher temperatures can also be tolerated and no other sol-vents need to be added as vinyl chloride can be vaporized to remove heat

In this same time frame, there was continuing development of the catalyst systems to improve effi ciency and to increase rate and yield At Dow and at Idemitsu, as well as in several other research laboratories, the development

of soluble metallocene catalysts for olefi n polymerization was occurring at the same time that SPS development was under way The activation of these metallocene - based catalysts with MAO or with other anionic counterions allows for highly effi cient and selective olefi n polymerization By careful manipulations of the ligand structure, the selectivity and effi cacy of these metallocenes became a signifi cant breakthrough in the catalysis for SPS

as well In addition, the optimization of the MAO structure and the use of important activators and cocatalysts all contributed to tremendous improve-ments in catalyst technology for this polymerization The importance of these catalyst improvements for the SPS process cannot be overstated Those impro-vements in effi ciency allowed for the elimination of a deashing process step and thereby a signifi cant reduction in the capital and operating cost of a commercial plant

Concurrent with this rapid advancement in catalyst and process lopment, the product and application development for SPS was also in progress

It was realized early on that the commercial viability of SPS as a high temperature engineering plastic would rely on the effective use of the crystal-line phase of the material The glass transition temperature (Tg) of the amorphous phase of SPS is approximately 100 ° C, which is identical to that of the atactic amorphous polystyrene used throughout the world For that reason, the practical use of SPS at temperatures above 100 ° C requires that the modulus drop be mitigated through the use of reinforcing fi llers such as glass or carbon

-fi ber This is the same material science used for other engineering polymers such as PBT or nylon where reinforcing fi bers are added to bridge the crystal-line phase and to maintain the modulus and strength of the material above the Tg Glass fi ber reinforcement of all these semicrystalline polymers requires good adhesion between the polymer matrix and the fi ber surface The pure polystyrene backbone does not offer signifi cant chemical bonding chemistry opportunities with its relatively inert phenyl ring and hydrocarbon backbone

To overcome this in a practical sense requires the correct silane surface tives for the glass fi bers and a compatible polymer phase with the SPS that will also chemically bond with that silane coupling agent Idemitsu and Dow developed several successful technical solutions to this and then optimized around the use of a proprietary modifi ed polymer additive during the extru-sion compounding step This system enabled the effective reinforcement required and was a key development leading to a number of products from 15% to 45% glass fi ber content for various applications

addi-10 HISTORICAL OVERVIEW AND COMMERCIALIZATION OF SYNDIOTACTIC POLYSTYRENE

Other important product developments that were worked on during this time included:

• nucleating agents to improve the apparent rate of crystallization and to facilitate better injection molding products

• thermal and oxidative stabilizers to allow for processing at temperatures above the melting point up to ∼ 320 ° C and for long - term application durability

• ignition - resistant additives for applications requiring that the plastic meet certain regulations with regard to fl ame and ignition tests

An additional need in some applications was for improved impact tance in both unfi lled and fi lled grades Unmodifi ed atactic polystyrene (APS) itself is a brittle polymer There are several ways in which it is modifi ed to improve the impact strength and to allow its range of application to be expanded High - impact polystyrene (HIPS) and acrylonitrile – butadiene – sty-rene (ABS) copolymer are just two examples for APS Below its glass transi-tion temperature, SPS brittle fracture is very similar to APS Research to improve SPS toughness followed similar strategies of adding impact modifi ers that allowed for absorption of energy on impact without initiating large cracks that would propagate rapidly and cause failure of parts In general, this involved the addition of compatible polymers, copolymers, or graft copoly-mers with glass transition temperatures below zero One complication for SPS over APS in this regard is the upper use temperatures required APS is only useful to a point just below Tg since it will lose modulus and therefore dimen-sional properties above Tg In that case, butadiene - based or other unsaturated rubber copolymers can be used to toughen it For SPS, researchers were faced with the fact that as an engineering plastic, it would be used well above Tg to temperatures where oxidative degradation of these unsaturated rubber mate-rials would be an issue in long - term use

It was therefore important for researchers to develop toughened grades with polymer additives that were resistant to thermal oxidation, and one very good way to accomplish this is with saturated styrene ethylenebutylene styrene (SEBS) block copolymers These copolymers are used already as tougheners for some APS systems when improved oxidative stability is needed They are highly compatible with the amorphous regions of the SPS matrix and they act

to absorb energy through some crazing and crack blunting mechanisms Researchers at Idemitsu also took advantage of the miscibility of APS and SPS to make PS /SPS blends (using HIPS as part or all of the polystyrene (PS) phase) to create a balanced blend of heat resistance, chemical resistance, and impact properties for some applications

The development of all these grades required extrusion melt compounding

of the SPS matrix and the various additives This required process research and development around the effective compounding of SPS above its melting

INTENSE DEVELOPMENT YEARS (1989–1996) 11

point of 270 ° C without thermal degradation of the polymer Compounding screw designs, addition sequences, die designs, and cooling and pelletizing equipment all had to be developed specifi cally to the needs of SPS Almost all of this information is know - how and trade secret to the compounding manufacturing process, but again is important in a historical sense to develop-ing the technology required to provide commercial grades

The market development efforts from 1990 to 1995 for these grades of compounded SPS revolved around applications requiring heat, chemical and electrical properties combined with ease of manufacture, and a unique property of dimensional stability for a semicrystalline plastic material This last property is due to the fact that the density of the crystalline and the amor-phous phases of SPS are almost identical This has the practical effect that the development of the crystalline phase during cooling does not impart warp or bow in fabricated parts to nearly the extent of most other polymers in this class

The major market areas that were targeted during this development phase included:

• electrical and electronics,

• automotive,

• appliance,

• packaging, and

• specialty fi lms and fi bers

Another historical development involved the need to develop fi lm and fi ber grade products with improved clarity and strength In this case, it is important

to develop products that take advantage of the high crystalline melting point but can be fabricated in such a way that strain applied at temperatures between

Tg and Tm induces that crystallization The pure homopolymer of SPS has an apparent crystallization rate that is high enough that it becomes very diffi cult

on a practical application basis to quench it from the melt phase and to keep

it uniformly amorphous Research in this case revolved around adding nomers that would slow down the crystallization rate enough without com-plete loss of crystallinity and without too much reduction in the melting point

In the early composition of matter, process and product patents that IKC had fi led, reference and claims to all types of substituted styrene homopoly-mers and copolymers in the syndiotactic confi guration had been made These became the practical basis for the development of fi lm and fi ber grade prod-ucts with improved (in this case reduced) crystallization rates from the melt The incorporation of small amounts of alkyl - substituted styrene monomers led to a new line of products for these markets and applications The almost complete random copolymer of para - methyl styrene and styrene with these catalysts is the basis of this technology Once it was discovered that this was effective, it was only a matter of optimizing the melt crystallization rate with