HANDBOOK OF POLYMERSYNTHESIS, CHARACTERIZATION,AND PROCESSING

HANDBOOK OF POLYMERSYNTHESIS, CHARACTERIZATION,AND PROCESSING

Edited by

ENRIQUE SALDıVAR-GUERRACentro de Investigacion en Quımica AplicadaSaltillo Coahuila, Mexico

EDUARDO VIVALDO-LIMAFacultad de Quımica, Universidad Nacional Autonoma de MexicoCiudad Universitaria, Mexico, D.F., Mexico

A JOHN WILEY & SONS, INC., PUBLICATION

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Library of Congress Cataloging-in-Publication Data:

Handbook of polymer synthesis, characterization, and processing / edited by Enrique Saldıvar-Guerra, Centro de Investigacion en Quımica Aplicada,Saltillo Coahuila, Mexico, Eduardo Vivaldo-Lima, Facultad de Quımica, Departamento de Ingenierıa Quımica, Universidad Nacional Autonoma deMexico, Mexico, D.F., Mexico.

pages cmIncludes bibliographical references and index.

ISBN 978-0-470-63032-7 (cloth)1. Polymerization. I. Saldıvar-Guerra, Enrique, editor of compilation. II. Vivaldo-Lima, Eduardo, editor of compilation.

TP156.P6H36 2013547′.28–dc23

2012025752

Printed in the United States of America

ISBN: 9780470630327

10 9 8 7 6 5 4 3 2 1

To Amparo, Adriana and Andres, with loveTo Adriana, Eduardo Abraham and Luis Angel, with appreciation and love

CONTENTS

PREFACE xv

ACKNOWLEDGMENTS xvii

CONTRIBUTORS xix

PART I BASIC CONCEPTS 1

1 Introduction to Polymers and Polymer Types 3Enrique Saldıvar-Guerra and Eduardo Vivaldo-Lima

1.1 Introduction to Polymers 31.2 Classification of Polymers 81.3 Nomenclature 12

References 13

2 Polymer States and Properties 15J. Betzabe Gonzalez-Campos, Gabriel Luna-Barcenas, Diana G. Zarate-Trivino,Arturo Mendoza-Galvan, Evgen Prokhorov, Francisco Villasenor-Ortega,and Isaac C. Sanchez

2.1 Introduction 152.2 Glass Transition Temperature (α-Relaxation) Controversy in Chitin,

Chitosan, and PVA 162.3 Glass Transition Related to the α-Relaxation 162.4 Moisture Content Effects on Polymer’s Molecular Relaxations 172.5 Dielectric Fundamentals 182.6 Chitin, Chitosan, and PVA Films Preparation for Dielectric

Measurements 212.7 Dielectric Relaxations in Chitin: Evidence for a Glass Transition 222.8 Dielectric Relaxations in Neutralized and Nonneutralized Chitosan:

The Stronger Water Content Effect on the α-Relaxation and the GlassTransition Phenomenon 30

2.9 PVA Dielectric Relaxations 35References 38

vii

viii CONTENTS

PART II POLYMER SYNTHESIS AND MODIFICATION 41

3 Step-Growth Polymerization 43Luis E. Elizalde, Gladys de los Santos-Villarreal, Jose L. Santiago-Garcıa,and Manuel Aguilar-Vega

3.1 Introduction 433.2 Polymerization Kinetics 463.3 Polyamides 483.4 Polyimides 503.5 Polyesters 503.6 Inorganic Condensation Polymers 533.7 Dendrimers 543.8 Thermoset Polycondensation Polymers 553.9 Controlled Molecular Weight Condensation Polymers 57

References 62

4 Free Radical Polymerization 65Ramiro Guerrero-Santos, Enrique Saldıvar-Guerra, and Jose Bonilla-Cruz

4.1 Introduction 654.2 Basic Mechanism 664.3 Other Free Radical Reactions 684.4 Kinetics and Polymerization Rate 714.5 Molecular Weight and Molecular Weight Distribution 744.6 Experimental Determination of Rate Constants 764.7 Thermodynamics of Polymerization 774.8 Controlled Radical Polymerization 78

References 81

5 Coordination Polymerization 85Joao B. P. Soares and Odilia Perez

5.1 Introduction 855.2 Polymer Types 875.3 Catalyst Types 875.4 Coordination Polymerization Mechanism 935.5 Polymerization Kinetics and Mathematical Modeling 93

References 101

6 Copolymerization 105Marc A. Dube, Enrique Saldıvar-Guerra, and Ivan Zapata-Gonzalez

6.1 Introduction 1056.2 Types of Copolymers 1066.3 Copolymer Composition and Microstructure 1076.4 Reaction Conditions: Considerations 118

References 121

7 Anionic Polymerization 127Roderic Quirk

7.1 Introduction 1277.2 Living Anionic Polymerization 1277.3 General Considerations 1297.4 Kinetics and Mechanism of Polymerization 134

CONTENTS ix

7.5 Stereochemistry 1447.6 Copolymerization of Styrenes and Dienes 1487.7 Synthetic Applications of Living Anionic Polymerization 150

References 157

8 Cationic Polymerizations 163Filip E. Du Prez, Eric J. Goethals, and Richard Hoogenboom

8.1 Introduction 1638.2 Carbocationic Polymerization 1638.3 Cationic Ring-Opening Polymerization 1728.4 Summary and Prospects 181

Acknowledgment 181References 181

9 Crosslinking 187Julio Cesar Hernandez-Ortiz and Eduardo Vivaldo-Lima

9.1 Introduction 1879.2 Background on Polymer Networks 1879.3 Main Chemical Routes for Synthesis of Polymer Networks 1919.4 Characterization of Polymer Networks and Gels 1939.5 Theory and Mathematical Modeling of Crosslinking 195Appendix A Calculation of Average Chain Length 200Appendix B Calculation of Sol and Gel Fractions 201

Acknowledgments 202References 202

10 Polymer Modification: Functionalization and Grafting 205Jose Bonilla-Cruz, Mariamne Dehonor, Enrique Saldıvar-Guerra, andAlfonso Gonzalez-Montiel

10.1 General Concepts 20510.2 Graft Copolymers 207

References 219

11 Polymer Additives 225Rudolf Pfaendner

11.1 Introduction 22511.2 Antioxidants 22711.3 PVC Heat Stabilizers 23111.4 Light Stabilizers 23311.5 Flame Retardants 23511.6 Plasticizers 23811.7 Scavenging Agents 23911.8 Additives to Enhance Processing 24011.9 Additives to Modify Plastic Surface Properties 24011.10 Additives to Modify Polymer Chain Structures 24111.11 Additives to Influence Morphology and Crystallinity

of Polymers 24211.12 Antimicrobials 24311.13 Additives to Enhance Thermal Conductivity 24311.14 Active Protection Additives (Smart Additives) 24311.15 Odor Masking 244

x CONTENTS

11.16 Animal Repellents 24411.17 Markers 24411.18 Blowing Agents 24411.19 Summary and Trends in Polymer Additives 245

References 245Further Reading 246

PART III POLYMERIZATION PROCESSES AND ENGINEERING 249

12 Polymer Reaction Engineering 251Alexander Penlidis, Eduardo Vivaldo-Lima, Julio Cesar Hernandez-Ortiz,and Enrique Saldıvar-Guerra

12.1 Introduction 25112.2 Mathematical Modeling of Polymerization Processes 25212.3 Useful Tips on Polymer Reaction Engineering (PRE) and Modeling 25712.4 Examples of Several Free Radical (Co)Polymerization Schemes

and the Resulting Kinetic and Molecular Weight DevelopmentEquations 264Acknowledgments 270References 270

13 Bulk and Solution Processes 273Marco A. Villalobos and Jon Debling

13.1 Definition 27313.2 History 27313.3 Processes for Bulk and Solution Polymerization 27413.4 Energy Considerations 28713.5 Mass Considerations 289

References 292

14 Dispersed-Phase Polymerization Processes 295Jorge Herrera-Ordonez, Enrique Saldıvar-Guerra, and Eduardo Vivaldo-Lima

14.1 Introduction 29514.2 Emulsion Polymerization 29514.3 Microemulsion Polymerization 30314.4 Miniemulsion Polymerization 30414.5 Applications of Polymer Latexes 30414.6 Dispersion and Precipitation Polymerizations 30514.7 Suspension Polymerization 30514.8 Controlled Radical Polymerization (CRP) in Aqueous

Dispersions 308References 310

15 New Polymerization Processes 317Eduardo Vivaldo-Lima, Carlos Guerrero-Sanchez, Christian H. Hornung,Iraıs A. Quintero-Ortega, and Gabriel Luna-Barcenas

15.1 Introduction 31715.2 Polymerizations in Benign or Green Solvents 31715.3 Alternative Energy Sources for Polymerization Processes 32715.4 Polymerization in Microreactors 329

CONTENTS xi

Acknowledgments 331References 331

PART IV POLYMER CHARACTERIZATION 335

16 Polymer Spectroscopy and Compositional Analysis 337Gladys de los Santos-Villarreal and Luis E. Elizalde

16.1 Introduction 33716.2 Elemental Analysis 33716.3 Infrared Spectroscopy 33916.4 Nuclear Magnetic Resonance of Polymers in Solution 34316.5 Mass Spectrometry 351

References 353

17 Polymer Molecular Weight Measurement 355Marıa Guadalupe Neira-Velazquez, Marıa Teresa Rodrıguez-Hernandez,Ernesto Hernandez-Hernandez, and Antelmo R. Y. Ruiz-Martınez

17.1 Introduction 35517.2 Historical Background 35517.3 Principles of GPC 35617.4 Measurement of Intrinsic Viscosity 362

References 365

18 Light Scattering and its Applications in Polymer Characterization 367Roberto Alexander-Katz

18.1 Introduction 36718.2 Principles of Static and Dynamic Light Scattering 36718.3 Static Light Scattering by Dilute Polymer Solutions 37018.4 Dynamic Light Scattering 377

References 387

19 Small-Angle X-Ray Scattering of Polymer Systems 391Carlos A. Avila-Orta and Francisco J. Medellın-Rodrıguez

19.1 Introduction 39119.2 Polymer Morphology 39119.3 Small-Angle X-Ray Scattering 39319.4 Analysis in Reciprocal Space 39519.5 Analysis in Real Space 399Appendix A Procedure to Obtain Morphological Data from 1D SAXS

Profiles 404References 406

20 Microscopy 409Mariamne Dehonor, Carlos Lopez-Barron, and Christopher W. Macosko

20.1 Introduction 40920.2 Transmission Electron Microscopy 40920.3 Three-Dimensional Microscopy 416

References 421

xii CONTENTS

21 Structure and Mechanical Properties of Polymers 425Manuel Aguilar-Vega

21.1 Structure of Polymer Chains 42521.2 Mechanical Properties of Polymers 42621.3 Mechanical Properties of Polymer Composites 431

References 434

PART V POLYMER PROCESSING 435

22 Polymer Rheology 437Estanislao Ortız-Rodrıguez

22.1 Introduction to Polymer Rheology Fundamentals 43722.2 Linear Viscoelasticity 44022.3 Viscometric Techniques for Polymer Melts 44122.4 Overview of Constitutive Equations 44322.5 Brief Overview on Other Relevant Polymer Rheology Aspects 445

References 448

23 Principles of Polymer Processing 451Luis F. Ramos-de Valle

23.1 General 45123.2 Compounding 45123.3 Extrusion 45223.4 Bottle Blowing 45523.5 Injection Molding 45523.6 Thermoforming 460

References 461Further Reading 461

24 Blown Films and Ribbons Extrusion 463Jorge R. Robledo-Ortız, Daniel E. Ramırez-Arreola, Denis Rodrigue,and Ruben Gonzalez-Nunez

24.1 Introduction 46324.2 Extrusion Processes for Blown Films and Ribbons 46324.3 Equations 46524.4 Ribbon and Film Dimensions 46724.5 Cooling Process and Stretching Force 46724.6 Morphology and Mechanical Properties 469

References 472

25 Polymer Solutions and Processing 473Damaso Navarro Rodrıguez

25.1 Introduction 47325.2 Polymer Solution Thermodynamics and Conformation of Polymer

Chains: Basic Concepts 47425.3 Semidilute Polymer Solutions 48125.4 Processing of Polymer Solutions 482

References 488

CONTENTS xiii

26 Wood and Natural Fiber-Based Composites (NFCs) 493Jorge R. Robledo-Ortız, Francisco J. Fuentes-Talavera, Ruben Gonzalez-Nunez,and Jose A. Silva-Guzman

26.1 Introduction 49326.2 Background 49326.3 Raw Materials 49426.4 Manufacturing Process 49726.5 Properties of Composite Materials 49726.6 Durability 49826.7 Factors that Affect Decay of Wood–Plastic Composites 50026.8 Uses of Wood–Plastic Composites 501

References 501

27 Polymer Blends 505Saul Sanchez-Valdes, Luis F. Ramos-de Valle, and Octavio Manero

27.1 Introduction 50527.2 Miscibility in Polymer Blends 50527.3 Compatibility in Polymer Blends 50827.4 Techniques for Studying Blend Microstructure 50927.5 Preparation of Polymer Blends 51027.6 Factors Influencing the Morphology of a Polymer Blend 51127.7 Properties of Polymer Blends 51327.8 Applications of Polymer Blends 516

References 517

28 Thermosetting Polymers 519Jean-Pierre Pascault and Roberto J.J. Williams

28.1 Introduction 51928.2 Chemistries of Network Formation 52028.3 Structural Transformations During Network Formation 52128.4 Processing 52428.5 Conclusions 532

References 532

PART VI POLYMERS FOR ADVANCED TECHNOLOGIES 535

29 Conducting Polymers 537Marıa Judith Percino and Vıctor Manuel Chapela

29.1 Introduction 53729.2 Historical Background 53829.3 The Structures of Conducting Polymers 53929.4 Charge Storage 53929.5 Doping 54129.6 Polyanilines 54329.7 Charge Transport 54429.8 Syntheses 54529.9 Conducting Polymers 54529.10 Characterization Techniques 55129.11 Present and Future Potential 552

References 555

xiv CONTENTS

30 Dendritic Polymers 559Jason Dockendorff and Mario Gauthier

30.1 Introduction 55930.2 Dendrimers 56130.3 Hyperbranched Polymers 56730.4 Dendrigraft Polymers 57430.5 Concluding Remarks 581

References 582

31 Polymer Nanocomposites 585Octavio Manero and Antonio Sanchez-Solis

31.1 Introduction 58531.2 Polyester/Clay Nanocomposites 58631.3 Polyolefin/Clay Nanocomposites 59031.4 Polystyrene/Clay Nanocomposites 59331.5 Polymer/Carbon Black Nanocomposites 59631.6 Nanoparticles of Barium Sulfate 59731.7 Polymer/Graphene Nanocomposites 59831.8 Conclusions 601

Acknowledgments 601References 601

INDEX 605

PREFACE

The industry of polymers is very complex, in part because itencompasses many aspects that are of multidisciplinary na-ture. The chain of production of polymers requires expertknowledge in different areas: (i) polymer synthesis, bothfrom the chemistry and the engineering aspects; (ii) poly-mer characterization, including chemical, physicochemical,rheological properties and others; and (iii) polymer process-ing and transformation into final products.

The aim of this handbook is to serve as the first sourceand comprehensive reference to all aspects of interest in thepolymer industry. Given the complexity of this industryand the specialized knowledge required in each area ofpolymer production and application, most of the booksdealing with polymer science and technology cover onlysome aspects of the polymer production chain; however, webelieve that a professional working in the polymer industryor, in general, in polymer science and technology wouldgreatly benefit from a book summarizing all the aspectsinvolved in the production chain of the polymer industry.The book has been written with the underlying idea ofmeeting this need. An effort has been made in every chapterto include the fundamentals of the chapter’s subject, therelevant literature, and the new trends in the field.

The book is addressed mainly to professionals in virtu-ally all positions in the polymer industry: manufacturing,quality control, R&D, sales, technical assistance, and so on.Another group of potential readers is the undergraduate andgraduate students in fields related to polymer science andtechnology. Finally, academic researchers of universitiesand institutes, working in different areas of polymerizationand polymers, will find the book useful for expanding theirknowledge beyond their area of expertise. The book canbe used to establish the first approach to a specific topic byanyone in the target audience, to broaden the knowledge

of industrial practitioners wanting to know more about thepolymer production chain, and to look for references inorder to deepen the understanding of specialized aspects ofa topic. It can also be used as a textbook in the first coursein polymer science or engineering, at the undergraduate orgraduate level, especially if a broad coverage of the fieldis desired.

After an introduction to the basic concepts of polymersand polymerization (Chapter 1) and thermodynamic poly-mer states (Chapter 2)1, the second part of the handbookis devoted to the main synthesis techniques of polymers(Chapters 3–5 and 7–8), including chapters covering con-cepts that may be applicable to all the synthesis techniques(crosslinking and grafting in Chapters 9 and 10, respec-tively). The important subject of copolymers (Chapter 6) isalso included in this section, as synthesis and structure areclosely related areas. The subject of additives is includedin the synthesis section because, from the point of view ofproperties and applications, they have become an importantpart of the polymeric material being synthesized. The thirdpart of the handbook is dedicated to the engineering prin-ciples and the different types of polymerization processesused in industry (Chapters 12–14); the new trends, froman engineering perspective, are also discussed (Chapter15). Part IV, which includes Chapters 16–21, provides thescope of the main techniques used for polymer characteri-zation and testing, at both the fundamental and the appliedlevels. Chapters 22–28 cover polymer processing princi-ples, techniques, and equipment. Chapter 28 (ThermosettingPolymers) is included here because of the emphasis on in-dustrial processes, although it implies simultaneous reactionand shaping. Finally, Chapters 29–31 deal with advanced

1Some important thermodynamic concepts related to polymers are dealtwith in Chapter 25.

xv

xvi PREFACE

and more specialized subjects in the polymer field, whichare of increasing importance (nanomaterials, dendrimers,and conjugated polymers).

The handbook represents the joint effort of a largenumber of scientists and researchers working in the many

diverse fields of polymer science and technology. Manyyears of study and experience have been put together inan organized manner in this work; hopefully, the handbookwill serve its purpose with a large audience.

ACKNOWLEDGMENTS

We are deeply grateful to the authors of all the chapters fortheir contribution and for sharing their expert knowledge.We also thank the Wiley-Blackwell editors and team fortheir support and guidance throughout the writing andediting of the handbook.

We also thank the several sponsors who have allowed usto carry out fundamental and applied research to an extentwhere we feel that we have added a few salt grains to thepolymer science and engineering fields. E.V.-L. is indebted

to UNAM (PAIP and PAPIIT Project 119510), CONA-CyT (Project 101682), and ICyTDF (Project PICSA11-56).E.S.-G. acknowledges CIQA and CONACyT for continu-ous support.

Last but not least, we thank our families for their supportand understanding during the editing of the handbook, andto some of our students and office staff at CIQA and FQ-UNAM for taking some extra work load that allowed us toinvest time in this project.

xvii

CONTRIBUTORS

Manuel Aguilar-Vega, Materials Unit, Membranes Labo-ratory, Centro de Investigacion Cientıfica de Yucatan,Merida, Yucatan, Mexico

Roberto Alexander-Katz, Departamento de Fısica, Uni-versidad Autonoma Metropolitana-Iztapalapa, Col. Vi-centina, Mexico

Carlos A. Avila-Orta, Centro de Investigacion en QuımicaAplicada, Saltillo, Coahuila, Mexico

Jose Bonilla-Cruz, Centro de Investigacion en MaterialesAvanzados, Apodaca, Nuevo Leon, Mexico

Vıctor Manuel Chapela, Laboratorio de Polımeros, Insti-tuto de Ciencias, Benemerita Universidad Autonoma dePuebla, Puebla, Pue., Mexico

Jon Debling, BASF Corp., Wyandotte, MI, USA

Mariamne Dehonor, Macro-M S.A. de C.V. Lerma, Edo.de Mexico, Mexico

Jason Dockendorff, Department of Chemistry, Institute forPolymer Research, University of Waterloo, Waterloo,Ontario, Canada

Filip E. Du Prez, Department of Organic Chemistry,Polymer Chemistry Research group, Ghent University,Ghent, Belgium

Marc A. Dube, Department of Chemical and Biolog-ical Engineering, Centre for Catalysis Research andInnovation, University of Ottawa, Ottawa, Ontario,Canada

Luis E. Elizalde, Centro de Investigacion en QuımicaAplicada, Saltillo, Coahuila, Mexico

Francisco J. Fuentes-Talavera, Departamento de Madera,Celulosa y Papel, Universidad de Guadalajara, LasAgujas, Zapopan, Jalisco, Mexico

Mario Gauthier, Department of Chemistry, Institute forPolymer Research, University of Waterloo, Waterloo,Ontario, Canada

Eric J. Goethals, Department of Organic Chemistry,Polymer Chemistry Research group, Ghent University,Ghent, Belgium

J. Betzabe Gonzalez-Campos, Universidad Michoacanade San Nicolas de Hidalgo, Instituto de InvestigacionesQuımico-Biologicas, Morelia, Michoacan, Mexico

Alfonso Gonzalez-Montiel, Macro M S.A. de C.V. Lerma,Edo. De Mexico, Mexico

Ruben Gonzalez-Nunez, Departamento de IngenierıaQuımica, Universidad de Guadalajara, Guadalajara,Jalisco, Mexico

Carlos Guerrero-Sanchez, CSIRO, Materials Science andEngineering Division, Victoria, Australia

Ramiro Guerrero-Santos, Centro de Investigacionen Quımica Aplicada, Saltillo, Coahuila, Mexico

Ernesto Hernandez-Hernandez, Centro de Investigacionen Quımica Aplicada, Saltillo, Coahuila, Mexico

Julio Cesar Hernandez-Ortiz, Departamento deIngenierıa Quımica, Facultad de Quımica, Univer-sidad Nacional Autonoma de Mexico, Mexico D.F.,Mexico

Jorge Herrera-Ordonez, Centro de Investigacionen Quımica Aplicada, Saltillo, Coahuila, Mexico

xix

xx CONTRIBUTORS

Richard Hoogenboom, Department of Organic Chemistry,Supramolecular Chemistry group, Ghent University,Ghent, Belgium

Christian H. Hornung, CSIRO, Materials Science andEngineering Division, Victoria, Australia

Carlos Lopez-Barron, Center for Neutron Science, De-partment of Chemical and Biomolecular Engineering,University of Delaware, Newark, DE, USA

Gabriel Luna-Barcenas, Centro de Investigacion y deEstudios Avanzados (CINVESTAV) del IPN, UnidadQueretaro, Queretaro, Queretaro, Mexico

Christopher W. Macosko, Dept. of Chemical Engineeringand Materials Science, University of Minnesota, Min-neapolis, MN, USA

Octavio Manero, Instituto de Investigaciones en Ma-teriales, Universidad Nacional Autonoma de Mexico,Mexico D.F., Mexico

Francisco J. Medellın-Rodrıguez, Facultad de CienciasQuımicas, Universidad Autonoma de San Luis Potosı,San Luis Potosı, San Luis Potosı, Mexico

Arturo Mendoza-Galvan, Centro de Investigacion y deEstudios Avanzados (CINVESTAV) del IPN, UnidadQueretaro, Queretaro, Queretaro, Mexico

Damaso Navarro Rodrıguez, Centro de Investigacion enQuımica Aplicada, Saltillo, Coahuila, Mexico

Marıa Guadalupe Neira-Velazquez, Centro de Inves-tigacion en Quımica Aplicada, Saltillo, Coahuila,Mexico

Estanislao Ortız-Rodrıguez, A. Schulman de Mexico, SanLuis Potosı, Mexico

Jean-Pierre Pascault, Universite de Lyon, UMR-CNRS 5223, INSA-Lyon, Ingenierie des MateriauxPolymeres/Laboratoire des Materiaux Macro-moleculaires, Villeurbanne, France

Alexander Penlidis, Department of Chemical Engineering,Institute for Polymer Research (IPR), University ofWaterloo, Waterloo, Ontario, Canada

Marıa Judith Percino, Laboratorio de Polımeros, Institutode Ciencias, Benemerita Universidad Autonoma dePuebla, Puebla, Pue., Mexico

Odilia Perez, Centro de Investigacion en Quımica Apli-cada, Saltillo, Coahuila, Mexico

Rudolf Pfaendner, Fraunhofer Institute for StructuralDurability and System Reliability LBF, Division Plas-tics, Darmstadt, Germany

Evgen Prokhorov, Centro de Investigacion y de EstudiosAvanzados (CINVESTAV) del IPN, Unidad Queretaro,Queretaro, Queretaro, Mexico

Iraıs A. Quintero-Ortega, Division de Ciencias eIngenierıas, Universidad de Guanajuato, Leon, Mexico

Roderic Quirk, Dept. of Polymer Science, The Universityof Akron, Akron, OH, USA

Daniel E. Ramırez-Arreola, Departamento de Ingenierıas,Universidad de Guadalajara, Autlan de Navarro, Jalisco,Mexico

Jorge R. Robledo-Ortız, Departamento de Madera, Celu-losa y Papel, Universidad de Guadalajara, Las Agujas,Zapopan, Jalisco, Mexico

Denis Rodrigue, Department of Chemical Engineeringand CERMA, Universite Laval, Quebec City, Quebec,Canada

Marıa Teresa Rodrıguez-Hernandez, Centro de Investi-gacion en Quımica Aplicada, Saltillo, Coahuila, Mexico

Antelmo R. Y. Ruiz-Martınez, Centro de Investigacion enQuımica Aplicada, Saltillo, Coahuila, Mexico

Enrique Saldıvar-Guerra, Centro de Investigacion enQuımica Aplicada, Saltillo, Coahuila, Mexico

Isaac C. Sanchez, Chemical Engineering Department, TheUniversity of Texas at Austin

Antonio Sanchez-Solis, Instituto de Investigacionesen Materiales, Universidad Nacional Autonoma deMexico, Mexico D.F., Mexico

Jose L. Santiago-Garcıa, Materials Unit, Membranes Lab-oratory, Centro de Investigacion Cientıfica de Yucatan,Merida, Yucatan, Mexico

Gladys de los Santos-Villarreal, Centro de Investigacionen Quımica Aplicada, Saltillo, Coahuila, Mexico

Jose A. Silva-Guzman, Departamento de Madera, Celulosay Papel, Universidad de Guadalajara, Las Agujas,Zapopan, Jalisco, Mexico

Joao B. P. Soares, Department of Chemical Engineering,University of Waterloo, Waterloo, Ontario, Canada

Saul Sanchez-Valdes, Centro de Investigacion en QuımicaAplicada, Saltillo, Mexico

Luis F. Ramos-de Valle, Centro de Investigacion enQuımica Aplicada, Saltillo, Mexico

Marco A. Villalobos, Cabot Corp., Billerica, MA, USA

Francisco Villasenor-Ortega, Department of BiochemicalEngineering, Instituto Tecnologico de Celaya, Celaya,Guanajuato, Mexico

Eduardo Vivaldo-Lima, Departamento de IngenierıaQuımica, Facultad de Quımica, Universidad NacionalAutonoma de Mexico, Mexico, D.F., Mexico

CONTRIBUTORS xxi

Roberto J. J. Williams, Institute of Materials Science andTechnology (INTEMA), University of Mar del Plata andNational Research Council (CONICET), Mar del Plata,Argentina

Ivan Zapata-Gonzalez, Facultad de Ciencias Quımicas,Universidad Autonoma de Coahuila, Saltillo, Coahuila,Mexico

Diana G. Zarate-Trivino, Centro de Investigacion y deEstudios Avanzados (CINVESTAV) del IPN, UnidadQueretaro, Queretaro, Queretaro, Mexico

PART I

BASIC CONCEPTS

1INTRODUCTION TO POLYMERS AND POLYMER TYPES

Enrique Saldıvar-Guerra and Eduardo Vivaldo-Lima

1.1 INTRODUCTION TO POLYMERS

1.1.1 Basic Concepts

Polymers are very large molecules, or macromolecules,formed by the union of many smaller molecules. Thesesmaller units are termed monomers before they areconverted into polymers. In fact, the word “polymer” has aGreek origin meaning “many members.” Natural polymershave been around since the early times in Planet Earth.Life itself is linked to polymers since deoxyribonucleic acid(DNA), ribonucleic acid (RNA), and proteins, which areessential to all known forms of life, are macromolecules.Cellulose, lignin, starch, and natural rubber are just afew other examples of natural polymers. Some of thesepolymers were used by early human civilizations to producesimple artifacts; for example, the play balls from naturalrubber for the ball game of several of the Mesoamericancivilizations (which contained ritual content and not onlyentertaining purposes). In the 1800s, natural polymersbegan to be chemically modified to produce many materials,such as vulcanized rubber, gun cotton, and celluloid.Although natural polymers are very important, this bookis mainly concerned with synthetic polymers, especiallyorganic synthetic polymers. The chemical reaction bywhich polymers are synthesized from monomers is termedpolymerization; however, this is a generic term, since thereare a number of chemical mechanisms involved in differentpolymerization reactions.

Synthetic polymers are relatively modern materials,since they entered into the technological and practical sceneonly in the first decades of the twentieth century. Thismakes them very different from some other materials thathave been known to humanity for centuries or millennia.

Handbook of Polymer Synthesis, Characterization, and Processing, First Edition. Edited by Enrique Saldıvar-Guerra and Eduardo Vivaldo-Lima.© 2013 John Wiley & Sons, Inc. Published 2013 by John Wiley & Sons, Inc.

Also, given the fact that synthetic polymers are created bychemical reactions, the possibilities of building differentpolymers are virtually endless, only restricted by chemicaland thermodynamic laws and by the creativity of thesynthetic polymer chemist. These endless possibilities havegiven rise to an enormous variety of synthetic polymersthat find application in almost every conceivable field ofhuman activity that deals with matter or physical objects. Inaddition, the enormous molecular structural versatility thatis derived from the rich synthetic possibilities, translatesinto materials with extremely diverse properties, andtherefore applications.

We can find polymers as components of many of theobjects that surround us, as well as in a broad diversityof applications in daily life: clothing, shoes, personal careproducts, furniture, electrical and electronic appliances,packaging, utensils, automobile parts, coatings, paints,adhesives, tires, and so on. The list is endless, and thesefew examples should provide an idea of the importance ofsynthetic polymers to modern society, in terms of both theirusefulness and the economic value that they represent.

1.1.2 History

Some synthetic polymers were inadvertently preparedsince the mid-nineteenth century by chemists working inorganic synthesis without necessarily knowing the chemicalstructure of these materials, although some of them mayhave had some intuition of the right character of thesemolecules as very large ones [1]. Only in 1920, Staudinger[2] proposed the concept of polymers as macromolecules,and this idea slowly gained acceptance among the scientificcommunity during the next decade. Some of the supporting

3

4 INTRODUCTION TO POLYMERS AND POLYMER TYPES

evidence for the macromolecular concept came frommeasurements of high molecular weight molecules inrubber using physicochemical methods. Later, around 1929,Carothers [3] started an experimental program aimed atthe synthesis of polymers of defined structures using well-known reactions of organic chemistry; this work, togetherwith the confirmation of high molecular weight moleculesby other experimental measurements (e.g., the viscosity ofpolymer solutions), helped to confirm the correctness of themacromolecular hypothesis of Staudinger. An interestingbook on the history of polymer science is that byMorawetz [4].

1.1.3 Mechanical and Rheological Properties

1.1.3.1 Mechanical Properties Long chains with highmolecular weights impart unique properties to polymers asmaterials. This can be illustrated by analyzing the changein the properties of the homologous series of the simplesthydrocarbon chains, the alkanes, which can be seen as con-stituted of ethylene repeating units (with methyl groups atthe chain ends),1 as the number of repeating units increase.At relatively low molecular weights (C6 –C10), compoundsin these series are relatively volatile liquids (gasolines). Asthe number of ethylene units increases, the compounds inthis series start to behave as waxes with low melting points.However, if the number of ethylene units exceeds some200–300, such that the molecular weight of the chains is inthe order of 5000–8000, the material starts to behave as asolid exhibiting the higher mechanical properties associatedwith a polymer (polyethylene in this case). In general,above some minimum molecular weight, polymers exhibitincreased mechanical properties and they are considered“high polymers”, alluding to their high molecular weight.

The mechanical behavior of a polymer is characterizedby stress–strain curves in which the stress (force perunit area) needed to stretch the material to a certainelongation is plotted. In order to experimentally generatethese curves, a tension stress is applied on a polymer sampleof known dimensions, which is elongated until it breaks.The elongation is expressed as a fractional or percentageincrease of the original length of the sample, which isdenominated strain, ε, and is defined as

ε = �L

L(1.1)

where L is the original length of the sample and �L isthe increase in length under the applied tension. The natureof the stress–strain curve for a given polymer defines its

1Strictly speaking, this is valid only for alkanes with a pair number ofcarbon atoms starting from butane, since ethylene has 2 C; however, thisprecision is irrelevant for this discussion (especially at high number ofcarbons).

possible use as elastomer, fiber, or thermoplastic. Figure 1.1shows the form of the stress–strain curves for these typesof polymers, and Table 1.1 shows typical values of some ofthe mechanical properties that can be defined as a functionof the stress–strain behavior.

The elastic or Young’s modulus is the initial slope of thestress–strain curve and gives a measure of the resistance todeformation of the material. The ultimate tensile strength isthe stress required to rupture the sample, and the ultimateelongation is the extent of elongation at which the ruptureof the sample occurs.

Mechanical properties are discussed here only in anintroductory manner in order to understand the mainapplications of polymers. An extended discussion of themechanical properties of polymers and their measurementcan be found in Chapter 21.

1.1.3.2 Rheological Properties Thermoplastics are pro-cessed and shaped in the molten state. This can be looselydefined as a state in which a polymer flows under the actionof heat and pressure. Molten polymers are non-Newtonianfluids, as opposed to the simpler Newtonian fluids. In thelatter, the stress σ (force per unit area) is proportional tothe shear rate γ (velocity per unit length) with a propor-tionality factor μ (viscosity) which is constant at a giventemperature. Newtonian fluids follow the law

σ = μγ (1.2)

On the other hand, in a non-Newtonian fluid, theviscosity depends on the shear rate. Besides showingvery high non-Newtonian viscosities, polymers exhibit acomplex viscoelastic flow behavior, that is, their flowexhibits “memory”, as it includes an elastic component inaddition to the purely viscous flow. Rheological propertiesare those that define the flow behavior, such as the viscosityand the melt elasticity, and they determine how easyor difficult is to process these materials, as well as theperformance of the polymer in some applications. Therheology of the polymers and its effect on the processingof these materials are studied in Chapters 22 and 23.

1.1.4 Polymer States

There are several scales at which polymers can be observed.The repeating unit in a polymeric chain lies in the scaleof a few angstroms, while a single polymer molecule orchain has characteristic lengths of a few to some tens ofnanometers (considering the contour length of a chain). Atthe next scale, or mesoscale, clusters of chains can be ob-served. This scale is rather important since it defines thepolymer morphology based on the order or disorder exhib-ited by the chains. Ordered regions are termed crystallineand disordered ones amorphous . In the crystalline regions,the polymer chains are packed in regular arrays termed

INTRODUCTION TO POLYMERS 5

102

103

104

105

10 2 3 4 5 6

13

4

2 1. Fiber2. Rigid plastic3. Flexible plastic4. Elastomer

e

s

Figure 1.1 Schematic stress–strain curves for different types of polymers.

TABLE 1.1 Typical Values of Mechanical Properties for Different Polymer Types

Type of Polymer (use) Modulus (N/m2) Typical Elongations (Strain %) Examples

Elastomers <2 × 106 400–1000 Polybutadiene, polyisoprene, butyl rubberFibers >2 × 109 100–150 Nylon (polyamide), polypropyleneFlexible thermoplastics 0.15−3.5 × 109 20–800 PolyethyleneRigid thermoplastics 0.7−3.5 × 109 0.5–10 Polystyrene, PMMA, phenol-formaldehyde resins

Abbreviation: PMMA, Poly(methyl methacrylate).

crystallites . Crystalline morphology is favored by structuralregularity in the polymer chain and by strong intermolec-ular forces, as well as by some chain flexibility. Usually,in a crystalline polymer, both ordered and disordered re-gions are found; thus, the so-called crystalline polymersare actually semicrystalline. Examples of highly crystallinepolymers are polyethylene and polyamides. On the otherhand, completely amorphous polymers that owe their disor-dered morphology to bulky substituents and rigid chains arecommon, atactic polystyrene and poly methyl methacrylatebeing good examples of this category.

There are two important thermal properties that definethe state of a polymer; these are the glass-transitiontemperature or Tg and the melting temperature, Tm. Belowthe glass-transition temperature, the amorphous regions ofa polymer are in a glassy state showing practically no chainmotions (at least in a practical time scale). Above the Tg, thepolymer behaves as a viscous liquid reflecting motions ofthe polymer chains or chain segments. Also, at the Tg, manyof the physicochemical properties of the polymer change ina relatively abrupt way (Fig. 1.2). The Tg can be definedin more precise thermodynamic terms, but this is furtherdiscussed in Chapter 2.

On the other hand, the Tm is a property exhibited bythe crystalline regions of a polymer and is the temperature

Tg1 Tg2 Tm2

Temperature (°C)

Spe

cific

vol

ume

(l/g)

1. Amorphous

2. Crystalline

1

2

Figure 1.2 Schematic representation of the main thermaltransitions in polymers in a plot of specific volume–temperature.

above which the crystalline regions melt and becomedisordered or amorphous. Since, for a given polymerTm > Tg, above the melting point, the polymer will flow asa viscous liquid. Amorphous polymers exhibit only a Tg,while semicrystalline polymers exhibit both, a Tg and a Tm.

6 INTRODUCTION TO POLYMERS AND POLYMER TYPES

1.1.5 Molecular Weight

Compounds made of small molecules exhibit a unique well-defined molecular weight; on the other hand, polymersexhibit a distribution of molecular weights since notall the polymer chains of a given sample will havethe same molecular weight or chain length. Therefore,in order to characterize a given polymer sample, it isnecessary to either describe the full molecular weightdistribution (MWD) or some average quantities related tothe distribution. Also, the MWD can be plotted in differentways using either length or weight for the abscissa and,for example, number average or weight average for theordinate; the classical paper of Ray [5] shows differentrepresentations of the MWD. Two of the most commonaverages are the number average and weight averagemolecular weights, Mn and Mw, respectively, which aredefined as

Mn =∑

x

f nx Mx (1.3)

Mw =∑

x

f wx Mx (1.4)

where f nx is the number fraction of chains having x

monomer units and Mx is the molecular weight of a chainhaving x monomer units. Also,

Mx = xM0 (1.5)

with M0 being the molecular weight of the monomer unit.f w

x is the weight fraction of chains having x monomerunits. In these definitions, and assuming long chains, thecontribution of any initiator fragment at the end of a chainhas been neglected. In mathematical terms, the number andweight fractions are defined as follows:

f nx = Nx∑

x

Nx

(1.6)

f wx = xNx∑

x

xNx

(1.7)

where Nx is the number of chains having x monomer units.Also note that

f wx = xNx∑

x

xNx

= xf nx∑

x

xf nx

(1.8)

Other related quantities that are frequently used arethe number average chain length (NACL) and the weightaverage chain length (WACL); also represented as rn andrw, respectively, in some texts. The NACL is also simply

termed the degree of polymerization or DPn . They aresimply related to Mn and Mw by the following equations:

NACL = Mn

M0(1.9)

WACL = Mw

M0(1.10)

Instead of giving average based on the weight of therepeating unit, these two quantities are based on the numberof repeating units.

1.1.5.1 Moments of the Molecular Weight DistributionSince the molecular weight is a distributed quantity, theconcepts and properties of statistical distributions canbe applied to the MWD. A statistical definition that isparticularly useful is that of moment of a distribution. Instatistics, the S th moment of the discrete distribution2 f ofa discrete random variable yi is defined as

μS =∞∑i=1

ySi f

(yi

), S = 0, 1, 2, . . . (1.11)

A graphical representation of the discrete distributionf (yi ) is shown in Figure 1.3a. Figure 1.3b shows theanalogous MWD represented as the (number) distributionf n

x of the discrete variable Mx (notice the equivalence of theconcept of distribution with those of fraction or frequency).

Equivalently, the S th moment of the MWD can bedefined as

μS =∞∑

X=1

MSx f n

x , S = 0, 1, 2, . . . (1.12)

Now, the average molecular weights of the MWD canbe more simply defined in terms of the moments (Eq. 1.12).

The number average molecular weight is simply

Mn = μ1

μ0(1.13)

since

μ1

μ0=

∞∑X=1

Mxfnx

∞∑X=1

f nx

= Mn

1(1.14)

2Notice that here we use the concept of distribution in a non-rigorousstatistical sense. In rigorous statistical terms “distribution” usually alludesto the cumulative distribution function. Here, as in common language, by“distribution” we mean what in rigorous statistical terms is denoted as“density function” or “probability function”.

INTRODUCTION TO POLYMERS 7

00

2

4

6

8

10

12

14

16

24 48 72 96 120 144 168 192 216 240 00

50

100

150

24 48 72 96 120 144 168 192 216 240

f(y

i)

yi Mx

fn x

(a) (b)

Figure 1.3 (a) A statistical discrete distribution (density) function f of the discrete randomvariable yi . (b) Example of a discrete molecular weight distribution of a polymer representedas the number distribution f n

x (or number fraction) of the discrete variable Mx .

Notice also that an equivalent physical definition ofMn is

Mn = Polymer mass

Polymer moles=

∑x

f nx Mx =

∑x

NxMx∑x

Nx

(1.15)

where the two right-most equalities come from applicationof Equations (1.3) and (1.6), respectively.

It is also possible to demonstrate (by application ofequations (1.12), (1.5), (1.8), and (1.4) in that order) that

Mw = μ2

μ1(1.16)

Averages based on higher order moments are also used,for example,

Mz = μ3

μ2; Mz+1 = μ4

μ3(1.17)

It should be emphasized that the discrete variable usedhere is Mx . In some textbooks and research papers, themoments of the MWD are defined in terms of the chainlength distribution (CLD) (with chain length, x , beingthe discrete variable), which means that, in that case, thecorresponding averages of the MWD defined in equationsanalogous to Equations (1.13), (1.16), and (1.17) need tobe multiplied by M0.

A special average that can be estimated by measurementsof the polymer solution intrinsic viscosity is the viscosimet-ric average molecular weight, which in terms of moments

is defined as

Mν =(

μα+1

μ1

)1/α

(1.18)

where α is the exponent in the Mark-Houwink-Sakuradaexpression:

[η] = KMαν (1.19)

in which [η] is the intrinsic viscosity of a polymer solutionand K and α are constants at a given temperature and fora given pair polymer–solvent [6].

Finally, the polydispersity index or molecular weightdispersity3 --D is defined as

--D = Mw

Mn

(1.20)

and it is a measure of the broadness of the MWD. It can bedemonstrated that --D is related to the variance of the MWDby the following expression:

σ 2Mx

= M2n (--D − 1) (1.21)

1.1.6 Main Types and Uses

In Section 1.2, we review in more detail the different criteriafor the classification of polymers; however, at this point,it is convenient to describe some of the main types ofpolymers according to their use. On the basis of this, they

3The term “dispersity” instead of “polydispersity index” is now recom-mended by the IUPAC [7].

8 INTRODUCTION TO POLYMERS AND POLYMER TYPES

can be identified as plastics, thermosets, elastomers, fibers,paints, and coatings. These uses naturally derive from someof the thermodynamic and mechanical properties of thepolymers, which were briefly described in Sections 1.1.3and 1.1.4.

Plastics or thermoplastics are materials that can beshaped under heating. Once they are heated above certaintemperature these materials flow as very viscous liquidsand can adopt the shape of a mold; once they are cooleddown again, they keep the new molded shape. In generalterms, this process of heating and molding can be repeateda number of times; however, after some reprocessingof this sort, the polymeric chains can break or undergoreactions leading to reduced physical properties, a fact thatsets practical limits to the recyclability of thermoplastics.Some of the most important thermoplastics by volumeare polyethylene (low density polyethylene (LDPE) andhigh density polyethylene (HDPE)), polypropylene (PP),poly(vinyl chloride) (PVC) and polystyrene (PS or PSt),to name a few. Thermoplastics are synthesized in largeamounts in polymerization plants and are then transformedby other users in processing equipment to form objectsuseful in packaging or as utensils, for example.

Thermosets , on the other hand, are polymers formed bythe mixing and chemical reaction of fluid precursors into amold; once the precursors react, a crosslinked network thatcannot flow anymore under heating is created; therefore,reaction and molding into the final shape usually takeplace at the same time (by the RIM or reaction injectionmolding process). Examples of common thermosets aresome polyesters, phenol-formaldehyde resins, epoxy resins,and polyurethanes, among others. Chapter 28 of thishandbook elaborates on this topic.

Elastomers or rubbers are flexible materials that aremainly used in tires, hoses, and seals; as adhesives;or as impact modifiers of thermoplastics. They exhibithigh resistance to impact, even at low temperatures atwhich materials increase their rigidity. For some of theapplications (e.g., tires or hoses), these materials have to beslightly crosslinked once they are formed into the desiredshape in order to impart them dimensional stability, sinceotherwise they tend to slowly flow. Elastomers are polymersthat are used above their glass-transition temperature (Tg).Some examples of common elastomers are polybutadiene,which is used as an impact modifier of rigid plastics;SBR (copolymer of styrene and butadiene), mainly usedin tires; EPDM (copolymer of ethylene, propylene, and adiene monomer, usually norbornene); NBR (copolymer ofacrylonitrile and butadiene); and so on.

Fibers are polymers with very high moduli and veryhigh resistance to deformation; therefore, they elongatevery little. Some examples of polymers used as fibers arenylon (polyamide), polyesters, and polyacrylonitrile (acrylicfiber).

Paints and coatings are based on polymers that can forma film. The polymer is considered the binder or vehicle thatcarries the pigments and additives that are used to impartcolor or protect the surface of the substrates on which thepaint or coating is applied. Some examples of polymersused as paint base are copolymers of styrene–butyl acrylateor of acrylic monomer–vinyl acetate. In the product, thepolymer is either finely dispersed in water forming a latexor dissolved in a solvent (in oil-based paints). Latexes forpaints are usually produced by emulsion polymerization(Chapter 14).

1.2 CLASSIFICATION OF POLYMERS

Given the versatility of polymers, they can be classifiedaccording to different criteria. In this section, we reviewsome of these classifications.

1.2.1 Classification Based on Structure

This is one of the oldest and most important classificationcriteria originally proposed by Carothers [3] in 1929and the one that splits polymers into two major types:addition and condensation polymers. The basis for thedistinction is better understood by illustration with twoexamples belonging each one to one category: polystyreneas an addition polymer and a polyester as a condensationpolymer. They are produced by the reactions shown inScheme 1.1.

In both the cases, the structure shown in parenthesisor brackets in the main product of the reaction is calledrepeating unit . In an addition polymer, the repeating unithas the same composition as that of the monomer; the onlydifference is the change of chemical bonds with respect tothose of the monomer. On the other hand, in a condensationpolymer, according to the original idea of Carothers, someatoms of the monomer are lost as a condensation compoundwhen the monomers react to form the repeating unitof the polymer. Some years after the original Carothersclassification, it became clear that some polymers, forexample, polyurethane, which is synthesized by the reactionbetween a diol and a diisocyanate, would not generate anycondensation molecule, so they could not be classified as acondensation polymer; still their chemistry and structurehad much more in common with those of condensationpolymers than with those of addition polymers; therefore,the criterion for classification of a polymer as one ofcondensation type was changed to include this type ofcases. The modern accepted criterion determines that acondensation polymer is that which satisfies any of thefollowing conditions: (i) some atoms of the monomer arelost as a small molecule during their synthesis or (ii) theycontain functional groups as part of the main polymer

CLASSIFICATION OF POLYMERS 9

H

H

H

n

n

C C

H

H

H

C C

nHO R1 OH +nHO2C R2 CO2H H O R1 OCO R2 COn

OH + (2n − 1)H2O

(a)

(b)

Scheme 1.1 Examples of the synthesis reactions of (a) anaddition polymer, polystyrene and (b) a condensation polymer,generic polyester with R1 and R2 being aliphatic or aromaticgroups.

chain, such as ester, urethane, amide, or ether. If a polymerdoes not satisfy any of these criteria then it is an additionpolymer.4 This issue is further discussed in Odian [8].

1.2.2 Classification Based on Mechanism

A second major classification of polymers was proposedby Flory [1] in 1953. This is based on the kineticmechanism of the polymerization reaction. Flory classifiespolymerizations into two categories:

1. Step-growth polymerization;

2. Chain polymerization.

1.2.2.1 Step-growth Polymerization The simplestscheme of this polymerization involves the reaction of adifunctional monomer AB, which contains both functionalgroups A and B in the molecule. For example, A can bean amine and B a carboxylic acid group. Another schemeinvolves the reaction between two difunctional monomersof the type AA and BB. In any case, each polymer linkagewill have involved the reaction of the functional groupsA and B coming from two molecules (monomers orchains). Some examples of polymers synthesized by thismechanism are polyurethane, polyamide, and polyester.

This mechanism shows the following features:

1. The chain growth occurs by steps; at each step,a reaction between the functional groups belongingto two monomers or chains occurs. If M1 denotesmonomer, M2 dimer, M3 trimer, and so on, themechanism can be schematically represented asfollows:

M1 + M1 → M2

M1 + M2 → M3

4IUPAC only defines the term polycondensation, but no condensationpolymers; however this last classification is of widespread use.

M1 + M3 → M4

M1 + M4 → M5

M2 + M2 → M4

M2 + M3 → M5

. . .

2. The size of the chains increases gradually andrelatively slowly.

3. Any two species in the system can react as long asthey possess unreacted dissimilar functional groups.

4. Monomer disappears at low conversions.

5. Conversion is measured in terms of the functionalgroups reacted.

1.2.2.2 Chain Polymerization This is characterized by:

1. It requires a generator of active centers (usually aninitiator for free radicals, anions, or cations).

2. Chain growth occurs by propagation of the activecenter (chain reaction of the active center withmonomer).

3. The monomer only reacts with active centers (notwith more monomer).

4. Monomer is present throughout all the reaction.

5. There is high molecular weight polymer presentat any time during the polymerization, so thecontents of the reaction at any time are unreactedmonomer, unreacted initiator, and high molecularweight polymer. There are no significant amounts ofintermediate size species (dimer, trimers, etc.).

6. Since there is a clear distinction between monomerand polymer, the conversion is measured in termsof the monomer already incorporated in a polymerchain.

7. The reaction mechanism for free radical polymeriza-tion as an example can be represented as follows:

Initiation : I → 2R

R + M → P1

Propagation : Pn + M → Pn+1

Termination : Pn + Pm → Dn + Dm or Dn+m

In the initiation steps, the initiator I decomposesgenerating two active centers (primary radicals) R, whichreact with a monomer M to produce an active polymerof length 1, P1, having an active center. The activepolymer grows by propagation of the active center addinga monomer unit in each propagation reaction. Finally, twoactive centers react, forming dead polymer of length n , Dn.

10 INTRODUCTION TO POLYMERS AND POLYMER TYPES

TABLE 1.2 Differences Between the Step-Growth and the Chain Polymerization Mechanisms

Feature Step-Growth Mechanism Chain (Living) Chain (with Termination)

Number and class of reactions Only one between dissimilargroups (A and B)

Two reactions: initiation andpropagation

Three reactions: initiation,propagation, and termination

Reactive species Two species of any size havingdissimilar groups

Active species of any size withmonomer

Active species of any size withmonomer or among them(termination)

Monomer consumption Monomer disappears early inthe reaction

Monomer is present up to highconversion

Monomer is present up to highconversion

Conversion On the basis of reactedfunctional groups

On the basis of polymerizedmonomer

On the basis of polymerizedmonomer

Average molecular weightversus conversion

Mn

X0.0 0.2 0.4 0.6 0.8 1.0

Mn

X0.0 0.2 0.4 0.6 0.8 1.0

Mn

X0.0 0.2 0.4 0.6 0.8 1.0

Source: Adapted from Ref 9. Copyright 1995, Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.

The differences between the step-growth and the chainpolymerization mechanisms are summarized in Table 1.2.Notice that chain polymerizations may include bimoleculartermination reactions (as in the free radical mechanism) ormay not (as in living anionic or cationic polymerizations).

Although sometimes the classifications of condensationand step-growth polymers are considered to be interchange-able, as well as those of addition and chain-growth poly-mers, one must be aware that the classification of a polymeronly by structure or only by mechanism may lead to ambi-guities. Odian [8] recommends to classify a polymer attend-ing both, structure and mechanism, in order to avoid thisproblem. Tables 1.3 and 1.4 contain examples of commonaddition and condensation polymers, respectively.

1.2.3 Classification by Chain Topology

Two polymers having the same chemical composition butdifferent chain topology can exhibit profound differences incrystallinity, physical properties, rheological behavior, andso on. For example, the differences in density, crystallinity,as well as mechanical and rheological properties of LDPEand HDPE derive from the presence or not of long andshort branches along the polymer chain. Linear chains arethose with no branches; these are shown schematically inFigure 1.4a. Branched chains have at least one branchalong the main chain. These branches are classified as short(usually less than 10 repeating units) or long, and theyare schematically illustrated in Figure 1.4b. Branches canalso be classified, according to Flory, as trifunctional ortetrafunctional, depending on the number of paths departingfrom the branching point. If the branches are formed byrepeating units (monomer) different from those forming

TABLE 1.3 Examples of Common Addition Polymers

Addition Polymers Repeating Unit

Polyacrylonitrile CH2 CH

CNPolybutadiene CH2

CH CH

CH2

Polyethylene CH2 CH2

Poly(methyl methacrylate)

CH2 C

CH3

CO2CH3

Polypropylene

CH2 CH

CH3

Polystyrene CH2 CH

φPoly(vinyl chloride) CH2 CH

Cl

the main chain, the branched polymer is a graft copolymer(Figure 1.4c, see also Chapter 6). Crosslinked polymersare those forming a three-dimensional network and areshown in Figure 1.4d; they are insoluble and have veryrestricted chain-segment mobility; therefore, they do notflow (a discussion on the processes leading to crosslinkedpolymers can be found in Chapter 9).

CLASSIFICATION OF POLYMERS 11

TABLE 1.4 Examples of Common Condensation Polymers

Polymer Synthesis Reaction → Repeating Unit

PolyamideH2N R1 NH2 HO2C R2 CO2H H NH R1 NHCO R2 CO OH

n+ H2O+

PolyesterHO R1 OH HO2C R2 CO2H H O R1 OCO R2 CO OH

n+ H2O+

Phenol-formaldehydeOH

+ CH2O

OH

CH2n

+H2O

Urea-formaldehyde H2N CO NH2 CH2O HN CO NH CH2 + H2On

+

PolyurethaneHO R1 OH + OCN R2 NCO O R1 OCO NH R2 NH CO

n

(a)(b)

(c) (d)

Figure 1.4 Different polymer chain topologies: (a) linear polymer; (b) branched polymer; (c)graft copolymer; and (d) crosslinked polymer. Dotson NE, Galvan R, Laurence RL, Tirrell M.Polymerization Process Modeling. VCH Publishers; 1995. p 35 [8]. Copyright 1995 Wiley-VCHVerlag GmbH & Co. KGaA.

1.2.4 Other Classification Criteria

1.2.4.1 Homopolymer and Copolymer If only one typeof monomer or repeating unit constitutes the macromolecule(without considering the chain ends) then the polymericsubstance is termed a homopolymer . If, on the other hand,more than one type of repeating unit is present in themacromolecule, the polymeric substance is a copolymer .The macromolecule produced in the specific case of areacting mixture containing three different monomers ormonomer units is termed terpolymer . Depending on therandomness or order in which two or more types ofrepeating units are present in the macromolecule, there are

different types of copolymers: random, block, alternate, andso on. These are described in Chapter 6.

1.2.4.2 Origin Another possible classification of poly-meric substances can be based on the origin of the materialor the repeating units. In this sense, one can have naturaland synthetic polymers, if they occur in nature or if theyare synthesized in a chemical laboratory, respectively. Ofcourse, natural polymers are of great importance, but theyfall out of the scope of this handbook, which is mainlyconcerned with synthetic polymers.

Also, among the synthetic polymers, one can distinguishbetween organic and inorganic polymers, depending on