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Editor A. M. van Herk Second Edition Chemistry and Technology of Emulsion Polymerisation
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Page 1: Chemistry and Technology of Emulsion Polymerisation · Technology of Emulsion Polymerisation Second Edition Editor A.M. van Herk Institute of Chemical and Engineering Sciences, Singapore

Editor A. M. van Herk

Second Edition

Chemistry and Technology of Emulsion Polymerisation

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Chemistry andTechnology of

EmulsionPolymerisationSecond Edition

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Chemistry andTechnology of

EmulsionPolymerisation

Second Edition

Editor

A.M. van Herk

Institute of Chemical and Engineering Sciences, Singapore

iii

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This edition first published 2013© 2013 John Wiley & Sons, Ltd

Registered officeJohn Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom

For details of our global editorial offices, for customer services and for information about how to apply for permission to reusethe copyright material in this book please see our website at www.wiley.com.

The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designsand Patents Act 1988.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or byany means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs andPatents Act 1988, without the prior permission of the publisher.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available inelectronic books.

Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and productnames used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. Thepublisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurateand authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is notengaged in rendering professional services. If professional advice or other expert assistance is required, the services of acompetent professional should be sought.

The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contentsof this work and specifically disclaim all warranties, including without limitation any implied warranties of fitness for aparticular purpose. This work is sold with the understanding that the publisher is not engaged in rendering professional services.The advice and strategies contained herein may not be suitable for every situation. In view of ongoing research, equipmentmodifications, changes in governmental regulations, and the constant flow of information relating to the use of experimentalreagents, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert orinstructions for each chemical, piece of equipment, reagent, or device for, among other things, any changes in the instructions orindication of usage and for added warnings and precautions. The fact that an organization or Website is referred to in this work asa citation and/or a potential source of further information does not mean that the author or the publisher endorses the informationthe organization or Website may provide or recommendations it may make. Further, readers should be aware that InternetWebsites listed in this work may have changed or disappeared between when this work was written and when it is read. Nowarranty may be created or extended by any promotional statements for this work. Neither the publisher nor the author shall beliable for any damages arising herefrom.

Library of Congress Cataloging-in-Publication Data applied for.

A catalogue record for this book is available from the British Library.

ISBN: 9781119953722

Set in 10/12pt Times by Aptara Inc., New Delhi, India.

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Contents

List of Contributors xiAbbreviations xiiiList of Frequently Used Symbols xviiIntroduction to the Second Edition xixIntroduction to the First Edition xxi

1 Historic Overview 1Finn Knut Hansen

1.1 The Early Stages 11.2 The Second Half of the Twentieth Century 9

1.2.1 Product Development 91.2.2 Kinetic Theory 111.2.3 Emulsion Polymerisation in Monomer Droplets 191.2.4 Industrial Process Control and Simulation 21

2 Introduction to Radical (Co)Polymerisation 23A.M. van Herk

2.1 Mechanism of Free Radical Polymerisation 232.2 Rate of Polymerisation and Development of Molecular

Mass Distribution 252.2.1 Rate of Polymerisation 252.2.2 Kinetic Chain Length 262.2.3 Chain Length Distribution 272.2.4 Temperature and Conversion Effects 30

2.3 Radical Transfer Reactions 312.3.1 Radical Transfer Reactions to Low Molecular Mass

Species 312.3.2 Radical Transfer Reactions to Polymer 32

2.4 Radical Copolymerisation 342.4.1 Derivation of the Copolymerisation Equation 342.4.2 Types of Copolymers 372.4.3 Polymerisation Rates in Copolymerisations 39

2.5 Controlled Radical Polymerisation 41

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vi Contents

3 Emulsion Polymerisation 43A.M. van Herk and R.G. Gilbert

3.1 Introduction 433.2 General Aspects of Emulsion Polymerisation 443.3 Basic Principles of Emulsion Polymerisation 463.4 Particle Nucleation 473.5 Particle Growth 51

3.5.1 The Zero-One and Pseudo-Bulk Dichotomy 523.5.2 Zero-One Kinetics 533.5.3 Pseudo-Bulk Kinetics 553.5.4 Systems between Zero-One and Pseudo-Bulk 57

3.6 Ingredients in Recipes 573.6.1 Monomers 583.6.2 Initiators 583.6.3 Surfactants 583.6.4 Other Ingredients 59

3.7 Emulsion Copolymerisation 593.7.1 Monomer Partitioning in Emulsion Polymerisation 593.7.2 Composition Drift in Emulsion Co- and

Terpolymerisation 633.7.3 Process Strategies in Emulsion Copolymerisation 64

3.8 Particle Morphologies 663.8.1 Core–Shell Morphologies 68

4 Emulsion Copolymerisation, Process Strategies 75Jose Ramon Leiza and Jan Meuldijk

4.1 Introduction 754.2 Monomer Partitioning 79

4.2.1 Slightly and Partially Water Miscible Monomers 794.2.2 Consequences of Monomer Partitioning for the Copolymer

Composition 844.3 Process Strategies 86

4.3.1 Batch Operation 864.3.2 Semi-Batch Operation 894.3.3 Control Opportunities 92

5 Living Radical Polymerisation in Emulsion and Miniemulsion 105Bernadette Charleux, Michael J. Monteiro, and Hans Heuts

5.1 Introduction 1055.2 Living Radical Polymerisation 106

5.2.1 General/Features of a Controlled/Living RadicalPolymerisation 106

5.2.2 Reversible Termination 1085.2.3 Reversible Chain Transfer 116

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Contents vii

5.3 Nitroxide-Mediated Polymerisation in Emulsion and Miniemulsion 1195.3.1 Introduction 1195.3.2 Control of Molar Mass and Molar Mass Distribution 1205.3.3 Synthesis of Block and Random or Gradient Copolymers via

(Mini)Emulsion Polymerisation 1255.3.4 Surfactant-Free Emulsion Polymerisation Using the

Polymerisation-Induced Self-Assembly Technique 1265.4 ATRP in Emulsion and Miniemulsion 126

5.4.1 Introduction 1265.4.2 Direct ATRP 1275.4.3 Reverse ATRP 1305.4.4 Next Generation ATRP Techniques: SRNI and AGET 1325.4.5 Some Concluding Remarks on ATRP in Emulsion 135

5.5 Reversible Chain Transfer in Emulsion and Miniemulsion 1365.5.1 Low Cex Reversible Chain Transfer Agents 1365.5.2 High Cex Reversible Chain Transfer Agents 137

5.6 Conclusion 143

6 Particle Morphology 145Yuri Reyes Mercado, Elena Akhmastkaya, Jose Ramon Leiza, and Jose M. Asua

6.1 Introduction 1456.2 Synthesis of Structured Polymer Particles 146

6.2.1 Emulsion Polymerisation 1466.2.2 Miniemulsion Polymerisation 1476.2.3 Physical Methods 148

6.3 Two-Phase Polymer–Polymer Structured Particles 1486.3.1 Effect of Grafting 152

6.4 Two-Phase Polymer–Inorganic Particles 1536.5 Multiphase Systems 1566.6 Effect of Particle Morphology on Film Morphology 162

6.6.1 Modelling Film Morphology 165Acknowledgements 165

7 Colloidal Aspects of Emulsion Polymerisation 167Brian Vincent

7.1 Introduction 1677.2 The Stabilisation of Colloidal Particles against Aggregation 1687.3 Pair-Potentials in Colloidal Dispersions 170

7.3.1 Core–Core Interactions 1707.3.2 Structural Interactions: (i) Those Associated with the Solvent 1717.3.3 Structural Interactions: (ii) Electrical Double Layer Overlap 1737.3.4 Structural Interactions: (iii) Adsorbed Polymer Layer Overlap 175

7.4 Weak Flocculation and Phase Separation in Particulate Dispersions 1797.5 Aggregate Structure and Strength 184

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viii Contents

8 Analysis of Polymer Molecules including Reaction Monitoringand Control 187Peter Schoenmakers

8.1 Sampling and Sample Handling 1888.1.1 Sampling 1888.1.2 Sample Preparation 188

8.2 Monomer Conversion 1898.3 Molar Mass 190

8.3.1 Molar-Mass Distributions 1918.4 Chemical Composition 197

8.4.1 Average Chemical Composition 1978.4.2 Molar-Mass Dependent Chemical Composition 1998.4.3 Chemical-Composition Distributions 2028.4.4 Two-Dimensional Distributions 207

8.5 Detailed Molecular Characterization 2108.5.1 Chain Regularity 2108.5.2 Branching 212

9 Particle Analysis 213Ola Karlsson and Brigitte E.H. Schade

9.1 Introduction 2139.2 Particle Size and Particle Size Distribution 214

9.2.1 Introduction 2149.2.2 Average Particle Diameter 2169.2.3 Particle Size Distribution 216

9.3 Sampling 2169.4 Particle Size Measurement Methods 217

9.4.1 Ensemble Techniques 2189.4.2 Particle Separation Methods 224

9.5 Comparison of Methods 2339.5.1 Choice of a Method 235

9.6 Particle Shape, Structure and Surface Characterisation 2369.6.1 Introduction to Particle Shape, Structure and Surface

Characterisation 2369.6.2 Classification of the Samples 2389.6.3 General Considerations – Sample Preparation If the Latex

is Film Forming 2389.7 Discussion of the Available Techniques 239

9.7.1 Optical Microscopy (OM) 2399.7.2 Atomic Force Microscopy (AFM) 2409.7.3 Electron Microscopy 2439.7.4 Indirect Analysis of Particle Morphology 2489.7.5 Surface Characterisation 2499.7.6 Cleaning of Latexes 2509.7.7 Analyses of Particle Charge 250

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Contents ix

9.7.8 Additional Techniques Used for Latex Particle SurfaceCharacterisation 250

9.7.9 Zeta Potential 251

10 Large Volume Applications of Latex Polymers 253Dieter Urban, Bernhard Schuler, and Jurgen Schmidt-Thummes

10.1 Market and Manufacturing Process 25310.1.1 History and Market Today 25310.1.2 Manufacturing Process 254

10.2 Paper and Paperboard 25410.2.1 The Paper Manufacturing Process 25410.2.2 Surface Sizing 25510.2.3 Paper Coating 256

10.3 Paints and Coatings 26210.3.1 Technology Trends 26310.3.2 Raw Materials for Water-Borne Coating Formulations 26410.3.3 Decorative Coatings 26910.3.4 Protective and Industrial Coatings 271

10.4 Adhesives 27110.4.1 Design of Emulsion Polymer Adhesives 27210.4.2 Formulation Additives 27610.4.3 Adhesive Applications 27710.4.4 Adhesive Test Methods 279

10.5 Carpet Backing 28010.5.1 Carpet Backing Binders 28110.5.2 Carpet Backing Compounds 28110.5.3 Application Requirements 282

Acknowledgements 282

11 Specialty Applications of Latex Polymers 283Christian Pichot, Thierry Delair, and Haruma Kawaguchi

11.1 Introduction 28311.2 Specific Requirements for the Design of Specialty Latex Particles 284

11.2.1 Nature of the Polymer 28411.2.2 Particle Size and Size Distribution 28511.2.3 Particle Morphology 28511.2.4 Nature of the Interface 28611.2.5 Surface Potential 28711.2.6 Colloidal Stability 28711.2.7 Functionality 287

11.3 Preparation Methods of Latex Particles for Specialty Applications 28811.3.1 Radical-Initiated Polymerisation in Heterogeneous Media 28811.3.2 Modification of Particles and Related Methods 29011.3.3 Formulation of Colloidal Dispersions from Pre-Formed

Polymers 293

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x Contents

11.4 Applications 29411.4.1 Non-Biomedical Applications 29411.4.2 Biological, Biomedical and Pharmaceutical Applications 299

11.5 Conclusions 304

References 307Index 337

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List of Contributors

Elena Akhmastkaya Basque Center for Applied Mathematics (BCAM), Spain

Jose M. Asua POLYMAT, University of the Basque Country UPV/EHU, Spain

Bernadette Charleux Chemistry, Catalysis, Polymers & Processes, Universite de Lyon,France

Thierry Delair Laboratoire des Materiaux Polymeres et des Biomateriaux, UniversiteClaude Bernard Lyon 1, France

R. G. Gilbert Centre for Nutrition & Food Science, University of Queensland, Australia,and Tongji School of Pharmacy, Huazhong University of Science and Technology, China

Finn Knut Hansen Department of Chemistry, University of Oslo, Norway

Ola Karlsson Division of Physical Chemistry, Lund University, Sweden

Haruma Kawaguchi Graduate School of Engineering, Kanagawa University, Japan

Hans Heuts Department of Chemical Engineering & Chemistry, Eindhoven Universityof Technology, The Netherlands

Jose Ramon Leiza POLYMAT, University of the Basque Country UPV/EHU, Spain

Yuri Reyes Mercado POLYMAT, University of the Basque Country UPV/EHU, Spain

Jan Meuldijk Department of Chemical Engineering & Chemistry, Eindhoven Universityof Technology, The Netherlands

Michael J. Monteiro Australian Institute for Bioengineering and Nanotechnology, TheUniversity of Queensland, Australia

Christian Pichot Saint-Priest, France

Brigitte E.H. Schade Particle Sizing Systems,Waterman, Holland

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xii List of Contributors

Jurgen Schmidt-Thummes BASF AG, GMD, Germany

Peter Schoenmakers Department of Chemical Engineering, University of Amsterdam,The Netherlands

Bernhard Schuler BASF AG, ED/DC, Germany

Dieter Urban BASF AG, GMD, Germany

A.M. van Herk Institute of Chemical and Engineering Sciences, Jurong Island,Singapore and Department of Chemical Engineering & Chemistry, Eindhoven Universityof Technology, The Netherlands

Brian Vincent School of Chemistry, University of Bristol, UK

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Abbreviations

AA Acrylic acidABS Acrylonitrile-butadiene-styreneAerosol MA AMA, sodium di-hexyl sulfosuccinateAerosol OT AOT, sodium di(2-ethylhexyl)sulfosuccinateAFM Atomic force microscopyAIBN AzobisisobutyronitrileATRP Atom transfer radical polymerizationB ButadieneBA n-Butyl acrylateBPO Benzoyl peroxydeBuna N Butadiene-acrylonitrile copolymerBuna S Butadiene-styrene copolymerCCA Colloidal crystalline arrayCCD Chemical composition distributionCDB Cumyl dithiobenzoateCFM Chemical force microscopyCFT Critical flocculation temperatureCMC Critical Micelle ConcentrationCMMD Control molar mass distributionCPVC Critical pigment volume concentrationCRP Controlled radical polymerization techniquesCTA Chain transfer agentsCVP Colloid vibration potentialCyclam TetrazacyclotetradecaneDLVO Derjaguin-Landau-Verwey-OverbeekDMA Dynamic mechanical analysisDNA Desoxy nucleic acidDSC Differential scanning calorimetryEDTA Ethylene diamino tetraacetic acidEHMA 2-Ethylhexyl methacrylateEPA Environmental Protection AgencyESA Electrokinetic sonic amplitudeESEM Environmental scanning electron microscopyFESEM Field emission scanning electron microscopyFIB-SEM focused ion beam SEM

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xiv Abbreviations

FFF Field-flow fractionationFLGN Feeney, Lichti, Gilbert and NapperHASE Hydrophobically modified alkali-swellable emulsionsHDPE High density polyethyleneHEC Hydroxy ethyl celluloseHEMA 2-Hydroxyethyl methacrylateHEUR Hydrophobically modified ethylene oxide urethanesHIC Hydrophobic interaction chromatographyHPLC High performance liquid chromatographyHUFT Hansen, Ugelstad, Fitch, and TsaiIR InfraredK KelvinLV-SEM low voltage SEMLRP Living radical polymerisationMA Methyl acrylateMFFT Minimum film forming temperatureMMA Methyl methacrylateMMD Molar Mass DistributionMONAMS A5 1-(methoxycarbonyl)eth-1-yl initiating radicalNMP Nitroxide-mediated living radical polymerisationNMR Nuclear magnetic resonanceNR Natural rubberOEM Original Equipment ManufacturerOM Optical microscopyPCH Phenyl-cyclohexenePCS Photon correlation spectroscopyPDI Polydispersity indexPDMS Poly(dimethylsiloxane)PEO Poly(ethylene oxide)PGA Poly(glycolic acid)PHS Poly(hydroxystearic acid)PLA Poly(D, L-lactic acid)PLGA Poly(glycolic-co-lactic acid)PMMA Poly(methylmethacrylate)PNIPAM Poly(N-isopropylacrylamide)PPO Polypropylene oxidePRE Persistent radical effectPSA Pressure sensitive adhesivesPSD Particle size distributionPTA Phosphotungstic acidPTFE Poly tetrafluorethylenePVAc Poly(vinyl acetate)PVC Pigment volume concentrationQCM-D quartz crystal micro-balance with dissipation monitoringRAFT Reversible addition fragmentation transferRCTA Reversible chain transfer agents

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Abbreviations xv

S StyreneSAM Self-assembled monolayerSANS Small angle neutron scatteringSAXS Small angle X-ray scatteringSB Styrene butadieneSBLC Styrene butadiene latex councilSBR Styrene butadiene rubberSDS Sodium dodecyl sulphateSed-FFF Sedimentation field-flow fractionationSEM Scanning electron microscopySFM Scanning force microscopySPM Scanning probe microscopySRNI Simultaneous reverse and normal initiationSSIMS Static secondary ion mass spectrometrySTM Scanning tunneling microscopyTEM Transmission electron microscopyTEMPO 2,2,6,6-Tetramethylpiperidine-l-oxylTexanol R©c 2,2,4-Trimethyl-1,3-pentanediol-diisobutyratUAc Uranyl acetateUV UltravioletVac Vinyl acetateVCH Vinyl-cyclohexeneVOC Volatile organic compoundW WattWet-SEM wet scanning transmission electron microscopyXPS X-ray photoelectron spectroscopyXSB Carboxylated styrene-butadiene dispersions

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List of Frequently Used Symbols

ae Specific surface area for a emulsifier molecule on a polymeric surfaceA Arrhenius constant of the initiation (Ai), propagation (Ap), termination (At) and

transfer (Atr)d average particle diameter dn, number average diameter, ds surface average diam-

eter, dw weight average diameter, dv volume average diameterdw/dn particle diameter non-uniformity factorE energy of activation for initiation (Ei), propagation (Ep), termination (Et) and

transfer (Etr)f Initiator efficiencyF Efficiency factor for adsorption�G Partial molar free energy of droplets �Gd, �Ga of the aqueous phase and of the

latex particles �Gl

H enthalpy�H change in enthalpyjcrit Critical length of an oligomer at which precipitation from the aqueous phase

occursk exit frequencyk rate constant of the initiation (ki), propagation (kp), termination (kt) and transfer

reaction (ktr)[M] concentration of monomer, [M]p concentration of monomer in the polymer parti-

cles. If this depends on quantities such as radius r, time t, etc., the recommendednotation is [M(r,t,. . .)]p. [M]a for the monomer concentration in the aqueousphase, [M]a,sat for the saturation concentration in the aqueous phase.

M average molar mass: number-average molar mass (Mn). weight-average molarmass (Mw),

N number of latex particles per unit volume of latexNn Number of particles with n radicals per particleNA Avogadro constantn number of radicals in a latex particlen average number of radicals per particlenm0 initially added number of moles of monomer per unit volume

Pnnumber average degree of polymerisation

R gas constantr1,2 reactivity parameters in copolymerisationrp rate of polymerisation per particle

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xviii List of Frequently Used Symbols

re rate of entry of radicals per particlert rate of termination per particlero the radius of the unswollen micelles, vesicles and/or latex particles.Rp Rate of polymerisationS entropy�S change in EntropyT temperatureTg glass transition temperaturet timeV volume of monomer swollen latex particlesVm molar volume of the monomervp volume fraction of polymerW stability ratiowp mass fraction of polymer in the particle phasex fraction conversion of monomer to polymerxn number-average degree of polymerisation, xw weight-average degree of poly-

merisationz-mer The length of an oligomer in the aqueous phase at which surface activity occursα fate parameter (fate of excited radicals)χ Flory-Huggins interaction parameterδ solubility parameter or chemical shiftε permittivityγ interfacial tensionη viscosity[η] intrinsic viscosityν kinetic chain lengthπ osmotic pressureρ entry frequencyρ i radical flux or rate of initiation (2 kd f [I])μ Volume growth factorτ g time of growth of a polymer chain

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Introduction to the Second Edition

The increasing need for environmentally benign production methods for polymers hasresulted in a further development and implementation of the emulsion polymerisation tech-nique. More and more companies switch from solvent based polymer production methodsto emulsion polymerisation.

Since the introduction of the first edition in 2005 the experience gained with using thisbook in a teaching environment, led us to this second improved edition. Besides some ofthe new developments we added a new chapter on latex particle morphology developmentas especially in this area much progress has been made and a lot of research efforts, both inacademia and in industry, has been devoted to this important area. Furthermore the chapteron the use of controlled radical polymerization in latex production has been substantiallyupdated as most of the other chapters.

Powerpoint slides of figures in this book for teaching purposes can be downloaded fromhttp://booksupport.wiley.com by entering the book title, author or isbn.

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Introduction to the First Edition

New polymerisation mechanisms like controlled radical polymerisation are combined withthe emulsion polymerisation technique, encountering specific problems but also leadingto interesting new possibilities in achieving special nanoscale morphologies with specialproperties. In the past years many people have been trained in the use of the emulsionpolymerisation technique. Many courses on the BSc, MSc and the PhD level as well asspecial trainings for people in industry are given all over the world. Despite this no recentbook exists with the purpose of supporting courses in emulsion polymerisation.

This book is aiming at MSc students, PhD students and reasonably experienced chemistsin university, government or industrial laboratories, but not necessarily experts in emulsionpolymerisation or the properties and applications of emulsion polymers. For this audience,which is often struggling with the theory of emulsion polymerisation kinetics, this bookwill explain how theory came about from well-designed experiments, making equationsplausible and intuitive. Another issue experienced, especially in industry, is that couplingtheory and everyday practice in latex production is really hard. This is another aim of thebook; showing how theory works out in real life.

The basis for the contents of this book can be found in the course emulsion polymerisationtaught for many years at the Eindhoven University of Technology in the framework ofthe Foundation Emulsion Polymerisation. Many people have contributed to shaping theaforementioned course and therefore laying a basis for this book: Ian Maxwell, JenciKurja, Janet Eleveld, Joop Ammerdorffer, Annemieke Aerdts, Bert Klumperman, Jos vander Loos and last but not least Ton German. Most of the contributors to the chapters aremember of the International Polymer Colloids Group, a group of experts around the worldthat meet on a regular basis and form a unique platform for sharing knowledge in the field.

The book is focussing on emulsion polymerisation in combination with both conventionaland controlled radical polymerisation. Except for miniemulsion polymerisation, more ex-otic techniques like inverse emulsion polymerisation, microemulsion polymerisation anddispersion polymerisation are not covered.

The first chapter is giving a historic overview of the understanding of emulsionpolymerisation, also focussing on the solution of the kinetic equations. In the secondchapter an introduction is given in the radical (co)polymerisation mechanism, explainingkinetics and the development of molecular weight and chemical composition. In chapterthree the basic element of emulsion polymerisation are explained, again focussing on rateof reaction and molecular mass distributions. In chapter four, emulsion copolymerisation,process strategies are explained. In chapter five the implementation of controlled radicalpolymerisation mechanisms in emulsion polymerisation is discussed. In Chapter 6 the

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xxii Introduction to the First Edition

development of morphology in latex production is discussed. Colloidal aspects of emulsionpolymerisation are discussed in chapter seven. In chapter eight an overview of themolecular characterization techniques of (emulsion) polymers is given whereas in chapternine the characterization techniques available for particle size, shape and morphologyare reviewed. In Chapter ten and eleven bulk and specialty applications are discussed. Asmuch as possible the nomenclature for polymer dispersions according to IUPAC has beenfollowed (Slomkowski, 2011).

We hope that this book will become a standard textbook in courses in emulsionpolymerisation.

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1Historic Overview

Finn Knut HansenDepartment of Chemistry, University of Oslo, Norway

1.1 The Early Stages

Polymers are composed of very large molecules, each of which includes a large numberof repeating structural units. The oldest and most abundant group of polymers consists ofthe natural polymers, such as cellulose, proteins, rubbers, and so on. One of these, naturalrubber, occurs in the form of a latex, that is defined as the “viscid, milky juice secreted bythe laticiferous vessels of several seed-bearing plants, notably Castillia elastica,” and so on(Bovey et al., 1955). By far the most important natural latex is that obtained from the rubbertree Hevea brasiliensis. This tree, originally from Brazil, as may be deduced from its name,was transplanted to Malaya, Sri Lanka and the East Indies (Hauser, 1930) in 1876, andeventually has made this area the most important source of natural rubber. The latex that isobtained from the tree is usually denoted as “natural latex” and is a colloidal suspensionof rubber particles stabilized by protein. The rubber content of the latex is between 32 and38% by weight, the protein 1 to 2%, different natural sugars about 2% and about 0.5% ofinorganic salts (Hauser, 1930). The rubber particles vary largely in size from quite small,circa 50 nm, up to 1–2 micrometres. The rubber latex is coagulated, washed and workedinto sheets that form the basis for further industrial use.

In view of the latex origin of natural rubber, it was not surprising that, when the needfor a synthetic equivalent arose, the mimicking of natural rubber latex was an obviousstarting point. The effort, and great success, of making synthetic rubber by emulsionpolymerisation has led to the word “latex” eventually being used to refer to a colloidalsuspension of synthetic polymers, as prepared by emulsion or suspension polymerisation.Such synthetic latexes are to be distinguished from dispersion of polymers prepared bygrinding the polymer with water and a dispersing agent. This chapter will treat the early

Chemistry and Technology of Emulsion Polymerisation, Second Edition. Edited by A.M. van Herk.© 2013 John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd.

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2 Chemistry and Technology of Emulsion Polymerisation

stages of the “invention” and production of synthetic latexes by emulsion polymerisationfrom the beginning and up to the middle of the twentieth century. Several reviews andbook chapters on the early developments in emulsion polymerisation have already beenwritten, and have been a natural starting point for this text. One of the first reviews is thatof Hohenstein and Mark from 1946 (Hohenstein and Mark, 1946). The following is a directquotation from their work (reprinted from J. Polymer Sci., by permission):

The earliest observations on polymerisation of olefins and diolefins as far back as 1838 (Markand Rafft, 1941; Regnault, 1838) refer almost entirely to the pure liquid phase and describe thegradual transition from a liquid monomer to a viscous or solid polymer under the influence ofheat, light, or a catalytically active substance. The idea of using a finely divided monomer inan aqueous suspension or emulsion seems to have been first conceived, about 1910, by Hofmanand Delbruck (Hofman and Delbruck, 1909, 1912) and Gottlob (Gottlob, 1913). There weretwo main reasons for the desire to carry out the polymerisation of various simple dienes in thepresence of a diluting agent: one, the fact that the use of metallic sodium as catalyst, which wascommon practice at that time, led to highly heterogeneous materials and posed a rather difficultproblem regarding the complete removal of the alkali metal from the final polymer. The moreimportant incentive for the use of an aqueous system, however, were the facts that all nativerubbers occur in the form of latexes and that, obviously, polymerisation in the plant takes placeunder mild conditions in an aqueous phase without the application of elevated temperaturesand high pressures, and certainly without the use of such catalysts as metallic sodium or alkalialkyls.

The aim of reproducing the physiological conditions occurring in the plant is mentionedin some of the earlier disclosures (Gottlob, 1913; Hofman and Delbruck, 1909, 1912), andled to the preparation and stabilization of the “emulsions” as described in these patents notwith the aid of soap or other surface-active agents, but by application of hydrophilic protectivecolloids such as gelatin, egg albumin, starch, milk, and blood serum. Certain remarks in thetext of these patents indicate that these protective colloids not only emulsify the hydrocarbonmonomer but may also act as catalysts during the polymerisation. We have carried out a numberof polymerisations, following closely the methods given as examples in two of these patentsand have substantially confirmed the results of the claims. In these experiments we observeda very slow, partial conversion of the monomer (isoprene, dimethylbutadiene) into a polymerlatex. The total amount of polymer formed varied between 40% and 80%; the duration of thereaction was in certain cases as much as six weeks. The results, in general very erratic andalmost irreproducible, create the impression that the reaction under such conditions could beconsidered a suspension polymerisation catalyzed by the oxygen of the air, which was neverspecifically excluded in any of the examples. In order to check this conclusion we repeated afew experiments of this type with deaerated monomer and deaerated water under nitrogen andfound that under these conditions only extremely slow polymerisation can be observed. In someinstances conversion was not achieved at all.

It seems, therefore, that the early practice, as disclosed in the above-mentioned patents, issubstantially different from what is known today as emulsion polymerisation, and is essentiallya suspension polymerisation in which the protective colloids act as suspension stabilizers andwhich is catalyzed by the presence of small amounts of oxygen.

In 1915 and 1916, Ostromislensky (Ostromislensky, 1915, 1916; Talalay and Magat, 1945)carried out similar experiments with vinyl halides and discussed the advantages of the presenceof an inert diluent. However, since there is no mention of the use of soap or other micelle-formingsubstances in his articles either, it seems that his observations also refer to “uncatalyzed” orphotocatalyzed polymerisation in solution and suspension.

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Historic Overview 3

It was only in 1927 that the use of soap and similar substances (ammonium, sodium, andpotassium oleates, sodium butylnaphthalene sulphonate) was disclosed in patents by Dinsmore(Dinsmore, 1927) and Luther and Heuck (Luther and Heuck, 1927). The examples cited in thesedisclosures approach present practice to a considerable degree; they specify the simultaneoususe of emulsifiers and catalyst (water- or monomer-soluble peroxides) and describe conversionsand reaction times of the same order of magnitude as reported in more recent scientific articles.It seems, therefore, that the use of catalyzed emulsion polymerisation is about twenty years old(in 1946, Ed. note).

In the years following a large number of additional patents accumulated, with an almost con-fusing multitude of disclosures and claims (compare references (Hoseh, 1940, 1941; Scheiber,1943; Talalay and Magat, 1945)). On the other hand, during this same period (1930–1940) onlyvery few articles were published in scientific journals. Dogadkin (1936) and his collaborators(Balandina et al., 1936a, 1936b; Berezan, Dobromyslowa, and Dogadkin, 1936) studied thepolymerisation of butadiene in the presence of soap, peroxides, and other catalysts at differenttemperatures and investigated the kinetics of this reaction. Fikentscher (Fikentscher, 1934),at a meeting of the Verein Deutscher Chemiker in 1938, gave a general description of thecourse of emulsion polymerisation of dienes and advanced, for the first time, the hypothesisthat polymerisation takes place essentially in the aqueous phase and not inside the monomerdroplets. In 1939, Gee, Davies, and Melville (Gee, Davies, and Melville, 1939) investigatedthe polymerisation of butadiene vapour on the surface of water containing a small amount ofhydrogen peroxide and came to certain conclusions about the kinetics of this process. While themechanism of emulsion polymerisation was thus only infrequently and briefly discussed in thescientific literature between 1930 and 1940, much work was carried out during this same periodin the research departments of various industrial organizations, as shown by the large numberof patents filed and issued in many countries.

One of the authors (H. M.) had an opportunity to discuss the problem of emulsion polymeri-sation in the period between 1935 and 1938 with Drs. Fikentscher, H. Hopff, and E. Valko inLudwigshafen am Rhine. At that time they offered several arguments in favour of polymerisationtaking place preponderantly in the aqueous phase. Valko even considered it as highly probablethat the monomer, solubilised in the micelles of the soap solution, was most favourably exposedto the action of a water-soluble catalyst and, therefore, might be considered as the principal site ofthe reaction. At a seminar on high polymers in Kansas City in September, 1945, Dr. F. C. Frylingtold us that he had, at the same time, independently arrived at very similar conclusions on thebasis of his own observations. It appears, therefore, that some of the more recent developmentswere anticipated to a certain extent in the unpublished work between 1930 and 1940.

No work in emulsion polymerisation was published in the next three years, except for briefreferences in the books of Mark and Raft (Mark and Rafft, 1941) and of Scheibler (Scheiber,1943). In 1941, Fryling (Fryling, 1944) described a very useful method for carrying out emulsionpolymerisation experiments in 10-gram systems and, together. with Harrington (Fryling andHarrington, 1944), investigated the pH of mixtures of aqueous soap solutions and substitutedethylenes, such as acrylonitrile, styrene, etc.; they concluded that the monomer which wassolubilized in the McBain layer micelles (McBain, 1942; McBain and Soldate, 1944) was verylikely to be the most important site for initiation of polymerisation. Hohenstein, Mark, Siggia,and Vingiello (Hohenstein, 1945; Hohenstein, Siggia, and Mark, 1944a; Hohenstein, Vigniello,and Mark, 1944b) studied the polymerisation of styrene in aqueous solutions without soapand in aqueous emulsions in the presence of soap. At the New York meeting of the AmericanChemical Society in September, 1944, Vinograd delivered three excellent lectures (Vinograd,Fong, and Sawyer, 1944) on the polymerisation of styrene in aqueous suspension and emulsion.At the same meeting, Frilette (Frilette, 1944) reported on experiments on the polymerisation ofstyrene in very dilute aqueous systems.

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4 Chemistry and Technology of Emulsion Polymerisation

In 1945, Hohenstein, Siggia, and Mark (Siggia, Hohenstein, and Mark, 1945) published anarticle on the polymerisation of styrene in agitated soap emulsions, and Hughes, Sawyer, andVinograd (Huges, Sawyer, Vinograd, 1945), Harkins (Harkins, 1945a), and Harkins with anumber of collaborators (Harkins 1945b) contributed very valuable x-ray data on the McBainmicelles (McBain, 1942) before, during, and after polymerisation. In the same year, two veryinteresting articles appeared, by Kolthoff and Dale (Kolthoff and Dale, 1945) and Price andAdams (Price and Adams, 1945), on the influence of catalyst concentration on the initial rate ofpolymerisation; and Montroll (Montroll, 1945) developed a general phenomenological theoryof processes during which diffusion and chemical reaction cooperate in the formation of largemolecules.

A large amount of basic research was carried out on all phases of emulsion polymerisation aspart of the government rubber program, most of which has not yet (1946, ed. note) been releasedfor publication. [The paper of Kolthoff and Dale (Kolthoff and Dale, 1945) was part of thisprogram and was published with the permission of the Rubber Reserve Company, Washington,D. C.] One can, therefore, look forward in the not too distant future to many informative articlesin this field.

As far as our present knowledge goes, it seems appropriate to distinguish between thefollowing three types of vinyl polymerisation of diluted monomers:

1. Polymerisation in homogeneous solution in which the monomer, all species of the polymermolecules, and the initiator (catalyst) are soluble in the diluting liquid (e.g., styrene poly-merisation in toluene with benzoyl peroxide). If the solution is sufficiently dilute, such aprocess begins and ends in a completely homogeneous system with a dilute molecular solu-tion of the monomer at the beginning and a dilute molecular solution of the various speciesof the polymer at the conclusion of the reaction. A number of recent papers (see originalpublication) describe studies on olefin polymerisations under such conditions. If the systemis not sufficiently dilute, toward the end of the reaction a concentrated polymer solution isobtained containing aggregations and entanglements of the macromolecules which representa certain deviation from molecularly homogeneous dispersion. A particularly interesting caseof solution polymerisation occurs if the monomer is soluble in the liquid, whereas certainspecies of the polymer, namely, those of higher degrees of polymerisation, are insoluble init. The polymerisation of styrene, the copolymerisation of vinyl chloride and vinyl acetatein methanol, and the polymerisation of acrylonitrile in water are examples of reactions thatstart in a molecularly homogeneous phase but continue and end in a system consisting of aswollen gel and a supernatant liquid solution.

2. Polymerisation in heterogeneous suspension, in which the monomer is mechanically dis-persed in a liquid, not a solvent for it and for all species of polymer molecules. The initiatoris soluble in the monomer. In such cases polymerisation takes place in each monomer globuleand converts it gradually into a polymer “bead” or “pearl”; the liquid plays only the role of acarrier, which favours heat transfer and agitation but does not interfere with the reaction assuch. The polymerisation of styrene or dichlorostyrene in aqueous dispersion is an exampleof such a process. It must, however, be noted that the monomer is never completely insolublein any carrier liquid and, in certain cases, such as bead polymerisation of vinyl acetate inwater, is even fairly soluble in it. These reactions are, then, processes in which solutionpolymerisation and suspension polymerisation occur simultaneously in the different phasesof the heterogeneous system-the former in the aqueous, the latter in the monomer, phase.The amount of polymer formed in each phase depends upon the solubility of the monomer inwater, and upon the distribution of the catalyst or catalysts in the two phases. If the monomeris only moderately soluble in water, the amount of polymer formed in the aqueous phaseis not considerable but its degree of polymerisation is low, because of the small monomer

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Historic Overview 5

concentration, and one obtains a polymer containing a noticeable amount of low molecularweight species. In fact, polymers prepared under such conditions occasionally show a molec-ular weight distribution curve with two distinct peaks, the smaller of which corresponds tothe lower molecular weight. This effect is exaggerated if, for some reason, one increasesthe solubility of the monomer in the aqueous phase by the addition of organic solvents likemethanol, alcohol, or acetone. This consideration shows that suspension polymerisation canbe a fairly complex process the complete elucidation of which is rather difficult. In the articleswhich attempt to contribute quantitative results (Hohenstein, 1945; Hohenstein, Vigniello,and Mark, 1944b; Vinograd, Fong, and Sawyer, 1944), monomers and catalysts were selectedwhich are only very slightly soluble in water and probably approach the case of a hetero-geneous suspension polymerisation to a fair degree. Another factor which may complicatethe elucidation of suspension polymerisation is the use of suspension stabilizers, which maysolubilize part of the monomer and, therefore, create an intermediate case between solutionand suspension polymerisation.

3. Polymerisation in emulsion, in which the monomer is: (a) dispersed in monomer dropletsstabilized by an adsorbed layer of soap molecules (Fryling and Harrington, 1944; Vino-grad, Fong, and Sawyer, 1944; Kolthoff and Dale, 1945; Price and Adams, 1945; Siggia,Hohenstein, and Mark, 1945); (b) solubilised in the soap micelles (McBain, 1942; McBainand Soldate, 1944; Harkins, 1945a) which exist in an aqueous soap solution of sufficientconcentration; and (c) molecularly dissolved in the water. The amount of polymer formed inthe droplets, in the micelles, and in solution will depend upon the way in which the monomerand catalyst are distributed in the three existing phases: the monomer phase, the soap mi-celle phase, and the water phase – and possibly also upon the accessibility and reactivityof the monomer in these three phases. In certain aqueous soap emulsions, such as styrene,dichlorostyrene, or isoprene, the amount of molecularly dissolved monomer is small and,therefore, the reaction will occur preponderantly either in the monomer droplets or in thesoap micelles. If the polymer formation occurs preponderantly in the micellar phase, oneis inclined to speak of a typical emulsion polymerisation. If, however, polymerisation takesplace to a considerable extent both in the monomer droplets and the soap micelles, the caseis intermediate between suspension and emulsion polymerisation. There also exist emulsionpolymerisations (vinyl acetate, acrylonitrile) in which the monomer is substantially solu-ble in water and a reaction which is a superposition of solution, suspension, and emulsionpolymerisation is expected.

These brief remarks suffice to show that one must select the system for investigation with careif complications and overlapping between different types of reactions are to be avoided.

This citation tells much about the early start of our understanding of the emulsionpolymerisation mechanisms, even though, at that time, a quantitative theory was not yetdeveloped. Basic understanding of the relative importance of the aqueous, organic and mi-cellar phases was also somewhat lacking. These topics will be treated thoroughly throughoutthis book. At this point, however, the very important, so-called, GR-S recipe for syntheticrubber must be mentioned. Even if the production of synthetic latexes was known in the1930s, the cost was higher that that of natural rubber. However, the need for large amountsof synthetic rubber arose as a result of World War II, after the Japanese conquests in SouthEast Asia. The secret United States Synthetic Rubber Program (1939–1945) resulted in thefamous GR-S rubber recipe, the so-called “Mutual” recipe that was used for the first timeby the Firestone and Goodrich companies in 1942 and adopted for large-scale productionin early 1943 (Bovey et al., 1955):

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6 Chemistry and Technology of Emulsion Polymerisation

Table 1.1 A typical recipe for a styrene-butadiene latex.

Ingredients Parts by weight

Butadiene 75Styrene 25Water 180Soap 5.0n-Dodecyl mercaptan 0.50Potassium persulfate 0.30

The American Chemical Society has declared this program as one of their “historicchemical landmarks”. By 1945, the United States was producing about 920 000 tons peryear of synthetic rubber, 85% of which was GR-S rubber. As we see (Table 1.1), the recipeis quite simple, and each ingredient has it specific function. The 3 : 1 ratio (5.8 : 1 molar) ofbutadiene and styrene gives the polymer its useful physical properties. In addition, butadienedoes not homopolymerise readily, and the copolymerisation with styrene gives the processa “normal” rate. The soap controls the nucleation and stabilization of the particles, whereasthe potassium persulfate acts as initiator. The traditional soap used was a commercial fattyacid soap containing mainly C16 and C18 soaps, but the effect of different soaps from C10 toC18 was investigated. The role of the mercaptan has been debated, and it has been frequentlystated that the mercaptan and persulfate form a redox couple. However, the most acceptedrole of the mercaptan is as an inhibitor and chain transfer agent: to inhibit the formationof cross-linked, microgel, particles during the polymerisation. When the rubber is used inend products, such as car tyres, and so on, it is cross-linked in its final shape, a process thatis called vulcanisation. This utilizes the tetra-functionality of the butadiene (two doublebonds), but this cross-linking is, naturally, not wanted during the emulsion polymerisation.Adding (amongst others) mercaptan to avoid this cross-linking action thus controls theprocess. The process is also stopped at 60–80% conversion and the monomers removed byflash distillation. The GR-S rubber recipe has been modified from the “Mutual” recipe overthe years. Especially, the lowering of the polymerisation temperature to 5 ◦C has improvedthe process by increasing the achievable molecular weight. That again makes it possible to“extend” the polymer by adding inexpensive petroleum oils and rosin derivatives. Becausepersulfate is too slow as an initiator at such low temperatures, the development of moreactive (redox) initiator systems was required.

In Germany, production of synthetic rubber had also been developed during theWar. These products were named Buna S (a butadiene-styrene copolymer) and BunaN (a butadiene-acrylonitrile copolymer) and these products were patented by the I.G.Farbenindustrie in the 1930s. In 1937 the annual German production of Buna S was5000 tons. Though these were much more expensive than natural rubber, productionwas pushed ahead for the very same reasons the American synthetic rubber programwas accelerated – the uncertain access to natural rubber under war conditions. After thewar, the know-how that had been developed both in Germany and in the US was used inmany other industrial emulsion polymerisation systems that began their development bothbefore and after the war. Another example of this is neoprene rubber, poly(chloroprene)


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