Principles of polymerization

4-2c Number of Polymer Particles / 3624-3 Other Characteristics of Emulsion Polymerization / 363 4-3f Molecular Weight and Particle Size Distributions / 365 4-3g Surfactant-Free Emulsion

PRI NCI PLES OF POLYMERIZATION Fourth Edition

GEORGE DOlAN

College of Staten Island

City University of New York

Staten Island, New York

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Library of Congress Cataloging-itl-Publication Data:

Prillciples or Pol.\'l1lerizatioll, FOllrlh Editioll

George Odian

ISBN 0-471-27400-3

Printed in the United States of America

1 INTRODUCTION

1-1 Types of Polymers and Polymerizations / I

1-1 a Polymer Composition and Structure / 2

I-I b Polymerization Mechanism / 6

1-2 Nomenclature of Polymers / 9

1-2a Nomenclature Based on Source / 10

1-2b Nomenclature Based on Structure (Non-IUPAC) / II

1-2e IUPAC Structure-Based Nomenclature System / 11

1-2d Trade Names and Nonnames / 16

1-3 Linear, Branched, and Crosslinked Polymers / 17

I A Molecular Weight / 19

1-5 Physical State / 24

1-5a Crystalline and Amorphous Behavior / 24

1-5b Determinants of Polymer Crystallinity / 27

1-5c Thermal Transitions / 29

1-6 Applications of Polymers / 32

1-6a Mechanical Properties / 32

1-6b Elastomers, Fibers, and Plastics / 35

References / 36

xxiii

1

2 STEP POLYMERIZATION

2-1 Reactivity of Functional Groups I 40

2-1 a Basis for Analysis of Polymerization Kinetics I 40

2-1 b Experimental Evidence I 41

2-1 c Theoretical Considerations I 43

2-1 d Equivalence of Groups in Bifunctional Reactants I 44

2-2 Kinetics of Step Polymerization I 44

2-2a Self-Catalyzed Polymerization I 46

2-2b External Catalysis of Polymerization I 51

2-2c Step Polymerizations Other than Polyesterification:

Catalyzed versus Uncatalyzed I 53

2-2d Nonequivalence of Functional Groups in Polyfunctional

2-4a Closed System I 65

2-4b Open Driven System I 67

2-4c Kinetics of Reversible Polymerization I 69

2-5 Cyclization versus Linear Polymerization I 69

2-5a Possible Cyclization Reactions I 69

2-5b Cyclization Tendency versus Ring Size I 70

2-5c Reaction Conditions I 72

2-5d Thermodynamic versus Kinetic Control I 73

2-5e Other Considerations I 74

2-6 Molecular Weight Control in Linear Polymerization I 74

2-6a Need for Stoichiometric Control I 74

2-6b Quantitative Aspects I 75

2-6c Kinetics of Nonstoichioll1etric Polymerization I 79

2-7 Molecular Weight Distribution in Linear Polymerization I 80

2-7a Derivation of Size Distributions I 80

2-7b Breadth of Molecular Weight Distribution I 82

2-7c Interchange Reactions I 83

2-7d Alternate Approaches for Molecular-Weight Distribution I 83

2-7e Effect of Reaction Variables on MWD I 86

39

2-8 Process Conditions I 87

2-8a Physical Nature of Polymerization Systems I 87

2-8b Different Reactant Systems I 89

2-10a Carothers Equation: X" -+ cx I 105

Mixtures / 106

2-IOb Statistical Approach to Gelation: X" -+ CXJ I 108

2-IOc Experimental Gel Points I III

2-10d Extensions of Statistical Approach / 112

2-11 Molecular Weight Distributions in Nonlinear Polymerizations I 114

2-13a Types of Copolymers I 135

2-13b Methods of Synthesizing Copolymers / 138

2-13c-3 Polvmer Blends and Interpenetrating Polymer

2-14 High-Performance Polymers / 144

2-14a Requirements for High-Temperature Polymers / 144

2-14b Aromatic Polyethers by Oxidative Coupling / 146

2-14c Aromatic Polyethers by Nucleophilic Substitution / 149

2-14d Aromatic Polysulfides / 151

2-14e Aromatic Polyimides / 151

2-14f Reactive Teleehelie Oligomer Approach / 155

2-14g Liquid Crystal Polymers / 157

2-14h 5-Membered Ring Heterocyclic Polymers / 159

2-14i 6-Membered Ring Heterocyclic Polymers / 162

2-14j Conjugated Polymers / 163

2-15 Inorganic and Organometallic Polymers / 168

2-l5a Inorganic Polymers / 168

2-15b Organometallic Polymers / 172

Bond / 173

2-16 Dendritic (Highly Branched) Polymers / 174

2-16a Random Hyperbranched Polymers / 175

2-16b Dendrimers / 177

2-17 Miscellaneous Topics / 180

2-17a Enzymatic Polymerizations / 180

2-17b Polymerization in Supereritical Carbon Dioxide / 183

2-17c Cycloaddition (Four-Center) Polymerization / 183

2-17d Spiro Polymers / 184

2-17e Pseudopolyrotoxanes and Polyrotoxanes / 184

References / 185

3 RADICAL CHAIN POLYMERIZATION

3-1 Nature of Radical Chain Polymerization / 199

198

3-1 a Comparison of Chain and Step Polymerizations / 199

3-1 b Radical versus Ionic Chain Polymerizations / 199

3-2 Structural Arrangement of Monomer Units / 202

3-2a Possible Modes of Propagation / 202

3-2b Experimental Evidence / 203

3-2c Synthesis of Head-to-Head Polymers / 204

3-3 Rate of Radical Chain Polymerization / 204

3-3a Sequence of Events / 204

3-3b Rate Expression / 206

3-3c Experimental Determination of RI' / 208

Product / 208

3-4 Initiation / 209

3-4a Thermal Decomposition of Initiators / 209

3-4b Redox Initiation / 216

3-4c Photochemical Initiation / 218

3-4d Initiation by Ionizing Radiation / 224

3-4e Pure Thermal Initiation / 226

3-41' Other Methods of Initiation / 227

3-4g Initiator Efficiency / 228

3-4h Other Aspects of Initiation / 235

3-6b Transfer to Monomer and Initiator / 240

3-6c Transfer to Chain-Transfer Agent / 245

3-6d Chain Transfer to Polymer / 250

3-6e Catalytic Chain Transfer / 254

3-7 Inhibition and Retardation / 255

3-7a Kinetics of Inhibition or Retardation / 256

3-7b Types of Inhibitors and Retarders / 259

3-7c Autoinhibition of Allylic Monomers / 263

3-8 Determination of Absolute Rate Constants / 264

3-8a Non-Steady-State Kinetics / 264

3-8b Rotating Sector Method / 265

3-8c PLP-SEC Method / 267

3-8d Typical Values of Reaction Parameters / 269

3-9 Energetic Characteristics / 271

3-9a Activation Energy and Frequency Factor / 271

3-9b Thermodynamics of Polymerization / 275

3-9c Polymerization-Depolymerization Equilibria / 279

3-10 Autoacceleration / 282

3-10a Course of Polymerization / 282

3-IOb Diffusion-Controlled Termination / 283

3-10c Effect of Reaction Conditions / 286

3-IOd Related Phenomena / 287

3-IOe Dependence of Polymerization Rate on Initiator and

Monomer / 288

3-lOf Other Accelerative Phenomena / 289

3- I I Molecular Weight Distribution / 289

3-1 Ia Low-Conversion Polymerization / 289

3-13d Other Processes; Self-Assembly and Nanostructures / 299

3-14 Specific Commercial Polymers / 300

3-15 Living Radical Polymerization / 313

3-15a General Considerations / 313

3-15b Atom Transfer Radical Polymerization (ATRP) / 316

3-15c Stable Free-Radical Polymerization (SFRP) / 325

3- I5d Radical Addition-Fragmentation Transfer (RAFT) / 328

3-15c Other Living Radical Polymerizations / 330

3-16 Other Polymerizations / 330

3-16a Organometallic Polymers / 330

4-2c Number of Polymer Particles / 362

4-3 Other Characteristics of Emulsion Polymerization / 363

4-3f Molecular Weight and Particle Size Distributions / 365

4-3g Surfactant-Free Emulsion Polymerization / 366

4-3h Other Emulsion Polymerization Systems / 367

4-3i Living Radical Polymerization / 368

References / 369

5-1 Comparison of Radical and Ionic Polymerizations / 372

5-2 Cationic Polymerization of the Carbon-Carbon Double Bond / 374

5-2a Initiation / 374

5-2c-3 Chain Transj'er to Polymer / 387

5-2d Kinetics / 388

5-2e Absolute Rate Constants / 392

5-2f Effect of Reaction Medium / 399

5-2h Energetics / 408

5-2i Commercial Applications of Cationic Polymerization / 410

5-2i-2 Other Products / 411

\ Anionic Polymerization of the Carbon-Carbon Double Bond / 4 I2

5-3a Initiation / 412

5-3b Termination / 416

Transjer Agents / 416

5-3c Group Transfer Polymerization / 420

5-3d Kinetics of Living Polymerization / 422

5-4 Block and Other Polymer Architectures / 436

5-4a Sequential Monomer Addition / 436

5-4b Telechelic (End-Functionalized) Polymers / 439

5-7a Monomers with Two Ditlerent Polymerizable Groups / 449

5-7b Hydrogen- Transfer Polymerization of Acrylamide / 450

5-7c Polymerization and Cyclotrimerization of Isocyanates / 451

5-7d Monomers with Triple Bonds / 451

6-2a Terminal Model; Monomer Reactivity Ratios / 466

6-2b Statistical Derivation of Copolymerization Equation / 469

6-2c Range of Applicability of Copolymerization Equation / 470

6-2d Types of Copolymerization Behavior / 471

6-2d-3 Block Copolymerization: rl > I, r2> 1 / 475

6-2e Variation of Copolymer Composition with Conversion / 475

6-21' Experimental Evaluation of Monomer Reactivity Ratios / 480

6-2g Microstructure of Copolymers / 481

6-2h Multicomponent Copolymerization / 485

6-3 Radical Copolymerization / 487

6-3a Etleet of Reaction Conditions / 487

464

6-3c Termina] Model for Rate of Radica] Copolymerization / 505

6-4 Ionic Copolymerization / 506

6-4a Cationic Copolymerization / 507

6-4b Anionic Copolymerization / 510

6-5 Deviations from Termina] Copolymerization Mode] / 5] 2

6-5a Kinetic Penultimate Behavior / 5]3

6-5b Depropagation during Copolymerization / 515

6-5c Copolymerization with Complex Participation / 518

6-5d Discrimination between Mode]s / 521

6-6 Copolymerizations Invo]ving Dienes / 52]

6-7a Miscellaneous Copolymerizations of Alkenes / 528

6-7b Copolymerization of Carbonyl Monomers / 528

7-I a Scope; Polymerizability / 545

7-1b Polymerization Mechanism and Kinetics / 5467-2 Cyclic Ethers / 548

7-2a Anionic Polymerization of Epoxides / 548

7-4 N-Carboxy-:x-Amino Acid Anhydrides / 578

7-4a Polymerization by Bases / 578

7-4b Polymerization by Transition Metal Complexes / 5807-5 Lactones / 581

7-5a Anionic Polymerization / 581

7-5b Cationic Polymerization / 583

7-5c Enzymatic Polymerization / 584

7-5d Other Cyclic Esters / 585

7-6 Nitrogen Heterocyclics / 586

7-6a Cyclic Amines / 586

7-6b Other Nitrogen Heterocyclics / 587

7-7 Sulfur Heterocyclics / 588

7-8 Cycloalkenes / 589

7-9 Miscellaneous Oxygen Heterocyclics / 592

7-10 Other Ring-Opening Polymerizations / 594

7-1/ Inorganic and Partially Inorganic Polymers / 595

7-II a Cyclosiloxanes / 595

7-II b Cyclotriphosphazenes / 597

7-II c Metallocenophanes / 599

7-II d Phosphorus-Containing Cyclic Esters / 599

7-lle Sulfur and Sulfur Nitride Polymers / 600

7-12 Copolymerization / 600

7-12a Monomers with Same Functional Group / 60 I

7-12b Monomers with Different Functional Groups / 603

8-1 c Carbonyl and Ring-Opening Polymerizations / 626

8-ld 1,3-Butadiene and 2-Substituted 1,3-Butadienes / 627

8-1 e I-Substituted and l,4-Disubstituted 1,3-Butadienes / 629

8-1 f Other Polymers / 631

8-2 Properties of Stereoregular Polymers / 633

8-2a Significance of Stereoregularity / 633

8-2b Analysis of Stereoregularity / 635

8-3 Forces of Stereoregulation in Alkene Polymerizations / 637

8-3a Radical Polymerization / 637

8-3b Ionic and Coordination Polymerizations / 640

8-4 Traditional Ziegler-Nalta Polymerization of Nonpolar Alkene

Monomers / 644

8-4a Historical Development of Ziegler-Natta Initiators / 644

8-4b Chemical Nature of Propagating Species / 645

8-4c Primary versus Secondary Insertion; Regioselectivity / 646

8-4d Propagation at Carbon-Transition Metal Bond / 647

8-4e Mechanism of Isoselective Propagation I 647

8-4f Mechanism of Syndioselective Propagation I 652

8-4g Direction of Double-Bond Opening I 654

8-4h Effects of Components of Ziegler-Natla Initiator I 655

8-4i Kinetics I 658

8-4i-2 Termination / 659

8-4i-3 Rate and Degree of Polymerization / 661

8-4i-4 Values of Kinetic Parameters / 662

8-4j Transition Metal Oxide Initiators I 664

8-5 Metallocene Polymerization of Nonpolar Alkene Monomers I 665

8-5a Metallocene Symmetry I 666

8-5b C2v-Symmetric Metallocenes I 668

8-5c C2-Symmetric Metallocenes I 668

8-5i Branching in Metallocene Polymerizations I 682

8-6 Other Hydrocarbon Monomers I 682

8-6a L2-Disubstituted Alkenes; Cycloalkenes I 682

8-6b Styrene I 683

8-6c Alkynes I 684

8-7 Copolymerization I 684

8-8 Postmetallocene: Chelate Initiators I 685

8-8a ansa-Cyclopentadienyl-Amido Initiators I 685

8-8b :x-Diimine Chelates of Late Transition Metals I 686

8-8c Phenoxy-Imine Chelates I 688

8-9 Living Polymerization I 689

8-10 Polymerization of 1,3-Dienes

8-lOa Radical Polymerization / 689

8-IOb Anionic Polymerization / 691

8-IOc Cationic Polymerization / 694

8-IOd Other Polymerizations / 695

8-llg Polymers from 1,3-Dienes / 699

8-12 Polymerization of Polar Vinyl Monomers / 699

8-12a Methyl Methacrylate / 699

8-l2b Vinyl Ethers / 703

8-13 Aldehydes / 703

8-14 Optical Activity in Polymers / 704

8-14a Optically Active Monomers / 704

8-14b Chiral Conformation / 704

8-14c Enantiomer-Differentiating Polymerization / 705

8-14d Asymmetric Induction / 707

8-15 Ring-Opening Polymerization / 707

8-16 Statistical Models of Propagation / 708

8-l6a Polymer Chain End Control / 708

8-16b Catalyst (Initiator) Site Control / 711

8-16c Application of Propagation Statistics / 712

9-2c Peroxide and Radiation Crosslinking / 742

9-2d Other Crosslinking Processes / 744

9-5a Natural Rubber / 748

9-5b Saturated Hydrocarbon Polymers / 749

9-6 Aromatic Substitution / 750

9-7 Cyclization / 751

9-8 Other Reactions / 752

9-9 Graft Copolymers / 752

9-9a Radical Graft Polymerization / 753

9-9b Anionic Graft Polymerization / 757

9-9c Cationic Graft Polymerization / 758

9-9d Other Approaches to Graft Copolymers / 7589-10 Block Copolymers / 759

9-11 Polymers as Carriers or Supports / 760

9-11 a Synthesis / 761

9-11 b Advantages of Polymer Reagents, Catalysts, andSubstrates / 764

9-12 Polymer Reagents / 765

regarding the reader's background, except for undergraduate organic and physical chemistry.Additionally, it is intended that the book will serve as a classroom text With the appropriateselection of materials, the text can be used at either the undergraduate or graduate level Eachchapter contains a selection of problems A solutions manual for the problems is availabledirectly from the author.

Many colleagues have been helpful in completing this new edition I am especiallyindebted to Chong Cheng, Krzysztof Matyjaszewski, and Stephen A Miller who graciouslygave their time to read and comment on portions of the text Their suggestions for improve-ments and corrections were most useful Ialso thank the many colleagues who generouslyresponded to my inquiries for their advice on various topics: Helmut G Alt, Jose M Asua,Lisa S Baugh Sabine Beuermann, Vincenzo Busico, Luigi Cavallo, John Chadwick, GeoffCoates, Scott Collins, James V Crivello, Michael F Cunningham, Thomas P Davis, Pieter J.Dijkstra, Rudolf Faust, Hanns Fischer, Michel Fontanille, Robert Gilbert, Alexei Gridnev,Richard A Gross Robert H Grubbs, Howard Haubenstock, Jorge Herrera-Ordonez, WalterHertler Hans Heuts Henry Hsieh, Aubrey Jenkins, Jaroslav Kahovec, Mikiharu Kamachi,Walter Kaminsky, Hans Kricheldorf, Morton Litt, Roberto Olayo, Patrick Lacroix-Desmazes,

W V Metanomski, Michael J Monteiro, Timothy E Patten, Stanislaw Penczek, Peter Plesch,Jorge Puig, Roderic P Quirk, Anthony K Rappe, Luigi Resconi, Ezio Rizzardo, GregRussell, Erling Rytter, Richard R Schrock, Donald Tomalia, Brigitte Voit, Kenneth Wagener,Robert M Way mouth, Owen W Webster, Yen Wei, David G Westmoreland, Edward S.Wilks, Bernard Witholt, Nan-Ioh Yang, Masahiro Yasuda, and Adolfo Zambelli Theirhelpful and insightful comments enriched and improved the text

I welcome comments from readers, including notice of typographical, factual, and othererrors

S/II/en IS{Ol/d, Nnr York 103 1-1 GEORGE OOIAN

Jill/I' 2003

g(!()/}l,codi{{l,((i'(I!t.I/C!

CHAPTER 1

INTRODUCTION

smaller molecules The small molecules that combine with each other to form polymer

mole-cules are termed monomers, and the reactions by which they combine are termed

polymer-izations There may be hundreds, thousands, tens of thousands, or more monomer molecules

linked together in a polymer molecule When one speaks of polymers, one is concerned withmaterials whose molecular weights may reach into the hundreds of thousands or millions

1-1 TYPES OF POLYMERS AND POLYMERIZATIONS

There has been and still is considerable confusion concerning the classification of polymers.This is especially the case for the beginning student who must appreciate that there is nosingle generally accepted classification that is unambiguous During the development ofpolymer science, two types of classifications have come into use One classification is based

on polymer structure and divides polymers into condensation and addition polymers The

other classification is based on polymerization mechanism and divides polymerizations

into step and chain polymerizations. Confusion arises because the two classifications areoften used interchangeably without careful thought The terms condensation and step are

often used synonymously, as are the terms addition and chain Although these terms may

often be used synonymously because most condensation polymers are produced by step merizations and most addition polymers are produced by chain polymerizations, this is notalways the case The condensation-addition classification is based on the composition orstructure of polymers The step-chain classification is based on the mechanisms of the poly-merization processes

poly-Principles ql Po!ymeri;:atio!1, Fourth Edition. By George Odian

ISBN 0-471-27400-3 Copyright (' 2004 John Wiley & Sons Inc.

1-1a Polymer Composition and Structure

Polymers were originally classified by Carothers [1929 J into condensation and addition mers on the basis of the compositional difference between the polymer and the monomer(s)from which it was synthesized Condensation polymers were those polymers that wereformed from polyfunctional monomers by the various condensation reactions of organicchemistry with the elimination of some small molecule such as water An example ofsuch a condensation polymer is the polyamides formed from diamines and diacids withthc elimination of water according to

poly-The common condensation polymers and the reactions by which they are formed are shown

in Table I-I It should be noted from Table I-I that for many of the condensation polymersthere are different combinations of reactants that can be employed for their synthesis.Thus polyamides can be synthesized by the reactions of diamines with diacids or diacylchlorides and by the self-condensation of amino acids Similarly, polyesters can be synthe-sized from diols by esterification with diacids or ester interchange with diesters

Some naturally occurring polymers such as cellulose, starch, wool, and silk are classified

as condensation polymers, since one can postulate their synthesis from certain hypotheticalreactants by the elimination of water Thus cellulose can be thought of as the polyetherformed by the dehydration of glucose Carothers included such polymers by defining conden-sation polymers as those in which the formula of the repeating unit lacks certain atoms that

are present in the monomer(s) from which it is formed or to which it may be degraded In this

sense cellulose is considered a condensation polymer, since its hydrolysis yields glucose,which contains the repeating unit of cellulose plus the elements of water

Addition polymers were classified by Carothers as those formed from nonomers withoutthe loss of a small molecule Unlike condensation polymers, the repeating unit of an additionpolymer has the same composition as the monomer The major addition polymers are thoseformed by polymerization of monomers containing the carbon-carbon double bond Such

monomers will be referred to as vinyl monomers throughout this text (The term vinyl, strictly

speaking, refers to a CH2=CH- group attached to some substituent Our use of the term

bond, including monomers such as methyl methacrylate, vinylidene chloride, and 2-butene

as well as vinyl chloride and styrene The term substituted ethylenes will also be used

inter-changeably with the term vinyl monomers.) Vinyl monomers can be made to react withthemselves to form polymers by conversion of their double bonds into saturated linkages,for example

where Y can be any substituent group such as hydrogen, alkyl, aryl, nitrile, ester, acid,ketone, ether, and halogen Table 1-2 shows many of the common addition polymers andthe monomers from which they are produced

The development of polymer science with the study of new polymerization processes andpolymers showed that the original classification by Carothers was not entirely adequate andleft much to be desired Thus, for example, consider the polyurethanes, which are formed bythe reaction of diols with diisocyanates without the elimination of any small molecule:

Using Carothers' original classiflcation, one would classify the polyurethanes as additionpolymers, since the polymer has the same elemental composition as the sum of the mono-mers However, the polyurcthanes are structurally much more similar to the condensationpolymers than to the addition polymers The urethane linkage (-NH-CO-O-) has much

in common with the ester (-CO-O-) and amide (-NH-CO-) linkages

To avoid the obviously incorrect classification of polyurethanes as well as of some otherpolymers as addition polymers, polymers have also been classified from a consideration ofthe chemical structure of the groups present in the polymer chains Condensation polymershave been defined as those polymers whose repeating units are joined together by functional

until eventually large-sized polymer molecules have been formed The characteristic of steppolymerization that distinguishes it from chain polymerization is that reaction occursbetween any of the different-sized species present in the reaction system.

The situation is quite different in chain polymerization where an initiator is used to duce an initiator species R*with a reactive center The reactive center may be either a freeradicaL cation, or anion Polymerization occurs by the propagation of the reactive center bythe successive additions of large numbers of monomer molecules in a chain reaction Thedistinguishing characteristic of chain polymerization is that polymer growth takes place bymonomer reacting only with the reactive center Monomer does not react with monomer andthe different-sized species such as dimer, trimer, tetramer, and n-mer do not react with eachother By far the most common example of chain polymerization is that of vinyl monomers.The process can be depicted as

pro-Each monomer molecule that adds to a reactive center regenerates the reactive center mer growth proceeds by the successive additions of hundreds or thousands or more monomermolecules The growth of the polymer chain ceases when the reactive center is destroyed byone or more of a number of possible termination reactions

Poly-The typical step and chain polymerizations differ significantly in the relationship betweenpolymer molecular weight and the percent conversion of monomer Thus if we start out stepand chain polymerizations side by side, we may observe a variety of situations with regard totheir relative rates of polymerization However, the molecular weights of the polymers pro-duced at any time after the start of the reactions will always be very characteristically dif-ferent for the two polymerizations If the two polymerizations are stopped at 0.1%

conversion, I% conversion, 10% conversion, 40% conversion, 90% conversion, and so on,one will always observe the same behavior The chain polymerization will show the presence

of high-molecular-weight polymer molecules at all percents of conversion There are nointermediate-sized molecules in the reaction mixture-only monomer, high-polymer, andinitiator species The only change that occurs with conversion (i.e., reaction time) is the con-tinuous increase in the number of polymer molecules (Fig I-I a) On the other hand, high-molecular-weight polymer is obtained in step polymerizations only near the very end of thereaction (>98% conversion) (Fig I-I b) Thus both polymer size and the amount of polymerare dependent on conversion in step polymerization

The classification of polymers according to polymerization mechanism, like that bystructure and composition, is not without its ambiguities Certain polymerizations show alinear increase of molecular weight with conversion (Fig I-I c) when the polymerization

Fig 1-1 Variation of molecular weight with conversion; (a) chain polymerization; (b) step tion; (c) nonterminating chain polymcrization and protein synthcsis.

polymeriza-mechanism departs from the normal chain pathway This is observed in certain chain merizations which involve a fast initiation process coupled with the absence of reactions thatterminate the propagating reactive centers Biological syntheses of proteins also show thebehavior described by Fig I-Ie because the various monomer molecules are directed to react

poly-in a very specific manner by an enzymatically controlled process

usually proceed by the chain polymerization mechanism, but the dependence of polymermolecular weight on conversion almost never follows the behavior in Fig I-I a Ring-open-ing polymerizations often follow the behavior in Fig I-I c.

The International Union of Pure and Applied Chemistry [IUPAC, 1994J suggested theterm fJolvcondensation instead of step polymerization, but polycondensation is a narrowerterm than step polymerization since it implies that the reactions are limited to condensa-tions-reactions in which small molecules such as water are expelled during polymerization.The term step polymerization encompasses not only condensations but also polymerizations

in which no small molecules are expelled An example of the latter is the reaction of diolsand diisocyantes to yield polyurethanes (Eq I -6) The formation of polyurethanes followsthe same reaction characteristics as the formation of polyesters, polyamides, and other poly-merizations in which small molecules are expelled

Ring-opening polymerizations point out very clearly that one must distinguish betweenthe classification of the polymerization mechanism and that of the polymer structure Thetwo classifications cannot always be used interchangeably Polymers such as the polyethersand polyamides produced in Eqs 1-10 and I-II, as well as those from other cyclic mono-mers, must be separately classified as to polymerization mechanism and polymer structure.These polymers arc structurally classified as condensation polymers, since they contain func-tional groups (e.g., ether, amide) in the polymer chain They, like the polyurethanes, are notclassified as addition polymers by the use of Carothers' original classification The situation

is even more complicated for a polymer such as that obtained from E-caprolactam The exactsame polymer can be obtained by the step polymerization of the linear monomer E-amino-caproic acid It should suffice at this point to stress that the terms condensation and step poly-mer or polymerization are not synonymous nor are the terms addition and chain polymer orpolymerization, even though these terms are often used interchangeably The classification ofpolymers based only on polymer structure or only on polymerization mechanism is often anoversimplification thaI leads to ambiguity and error Both structure and mechanism are usual-

ly needed in order to clearly classify a polymer

1-2 NOMENCLATURE OF POLYMERS

Polymer nomenclature leaves much to be desired A standard nomenclature system based onchemical structure as is used for small inorganic and organic compounds is most desired

Unfortunately, the naming of polymers has not proceeded in a systematic manner until

rela-tively late in the development of polymer science It is not at all unusual of a polymer to have

several names because of the use of different nomenclature systems The nomenclature tems that have been used are based on either the structure of the polymer or the source of thepolymer [i.e., the monomer(s) used in its synthesis] or trade names Not only have there beenseveral different nomenclature systems, but their application has not always been rigorous

sys-An important step toward standardization was initiated in the 1970s by the InternationalUnion of Pure and Applied Chemistry

1-2a Nomenclature Based on Source

The most simple and commonly used nomenclature system is probably that based on thesource of the polymer This system is applicable primarily to polymers synthesized from asingle monomer as in addition and ring-opening polymerizations Such polymers are named

by adding the name of the monpmer onto the prefix "poly" without a space or hyphen Thusthe polymers from ethylene and acetaldehyde are named polyethylene and polyacetaldehyde,

respectively When the monomer has a substituted parent name or a multiworded name or anabnormally long name, parentheses are placed around its name following the prefix "poly."The polymers from 3-methyl-I-pentene, vinyl chloride, propylene oxide, chlorotriftuoroethy-lene and c-caprolactam are named poly(3-methyl-I-pentene), poly(vinyl chloride), poly(pro-pylene oxide), poly(chlorotriftuoroethylene), and poly(€-caprolactam), respectively Otherexamples are listed in Table 1-2 The parentheses are frequently omitted in common usagewhen naming polymers Although this will often not present a problem, it is incorrect and insome cases the omission can lead to uncertainty as to the structure of the polymer named.Thus the use of polyethylene oxide instead of poly(ethylene oxide) can be ambiguous indenoting one of the following possible structures:

It should be noted that there is an ambiguity here in that poly(6-aminocaproic acid) andpoly(c-caprolactam) are one and the same polymer The same polymer is produced fromtwo different monomers-a not uncommonly encountered situation.

1-2b Nomenclature Based on Structure (Non-IUPAC)

A number of the more common condensation polymers synthesized from two differentmonomers have been named by a semi systematic, structure-based nomenclature system otherthan the more recent IUPAC system The name of the polymer is obtained by following the

prefix poly without a space or hyphen with parentheses enclosing the name of the structural

grouping attached to the parent compound The parent compound is the particular member ofthe class of the polymer-the particular ester, amide, urethane, and so on Thus the polymerfrom hexamethylene diamine and sebacic acid is considered as the substituted amide deriva-tive of the compound sebacic acid, H02C(CH2)gC02H, and is named poly(hexamethylenesebacamide) Poly(ethylene terephthalate) is the polymer from ethylene glycol and terephtha-lic acid, p-H02C-C6H4-C02H The polymer from trimethylene glycol and ethylene diiso-cyanate is poly(trimethylene ethylene-urethane)

A suggestion was made to name condensation polymers synthesized from two different

monomers by following the prefix poly with parentheses enclosing the names of the two

reac-tants, with the names of the reactants separated by the term -co-. Thus, the polymer in Eq 1-7would be named poly(phenol-co-formaldehyde) This suggestion did not gain acceptance

1-2c IUPAC Structure-Based Nomenclature System

The inadequacy of the preceding nomenclature systems was apparent as the polymer tures being synthesized became increasingly complex The IUPAC rules allow one to name

struc-single-strand organic polymers in a systematic manner based on polymer structure (IUPAC,

1991, 1994,2002, in press; Panico et aI., 1993; Wilks, 2000) Single-strand organic polymershave any pair of adjacent repeat units interconnected through only one atom All the poly-mers discussed to this point and the large majority of polymers to be considered in this textare single-strand polymers Douhle-strand polymers have uninterrupted sequences of rings

A ladder polymer is a double-strand polymer in which adjacent rings have two or more atoms

in common, for example, structure VII Some aspects of double-strand polymers are ered in Sees 2-l4a and 2-17d

consid-The basis of IUPAC polymer nomenclature system is the selection of a preferred

repeating unit The CRU is the smallest possible repeating unit of the polymer It is a bivalent

unit for a single-strand polymer The name of the polymer is the name of the CRU in entheses or brackets prefixed by poly The CRU is synonymous with the repeating unitdefined in Sec I-I a except when the repeating unit consists of two symmetric halves, as

par-in the polymers -+CH2CHrb- and +-CF 2 CF r1n' The CRU is CH2 and CF20 respectively,for polyethylene and polytetrafluoroethylene, while the repeating unit is CH2CH2 andCF2CF2, respectively

The constitutional repeating unit is named as mueh as possible aceording to the IUPACnomenclature rules for small organic compounds The IUPAC rules for naming single-strandpolymers dictate the choice of a single CRU so as to yield a unique name, by specifying both

the seniority among the atoms or subunits making up the CRU and the direction to proceed along the polymer chain to the end of the CRU A CRU is composed of two or more subunits

when it cannot be named as a single unit The following is a summary of the most important

of the IUPAC rules for naming single-stand organic polymers:

1 The name of a polymer is the prefix poly followed in parentheses or brackets by thename of the CRU The CRU is named by naming its subunits Subunits are defined as thelargest subunits that can be named by the IPUAC rules for small organic compounds

2 The CRU is written from left to right beginning with the subunit of highest seniorityand proceeding in the direction involving the shortest route to the subunit next in seniority

3 The seniority of different types of subunits is heterocyclic rings> heteroatoms oracyclic subunits containing heteroatoms > carbocyclic rings> acyclic subunits containingonly carbon The presence of various types of atoms, groups of atoms, or rings that are notpart of the main polymer chain but are substituents on the CRU do not affect this order ofseniority

4 For heterocyclic rings the seniority is a ring system having nitrogen in the ring> a ringsystem having a heteroatom other than nitrogen in the order of seniority defined by rule 5below> a ring system having the greatest number of heteroatoms > a ring system having thelargest individual ring> a ring system having the greatest variety of heteroatoms > a ringsystem having the greatest number of heteroatoms highest in the order given in rule 5

s. For heteroatom(s) or acyclic subunits containing heteroatom(s), the order ofdecreasing priority is S, Se, Te, N, P, As, Sb, Bi, Si, Ge, Sn, Pb, B, Hg (Any heteroatom

The higher seniority of cyclic subunits over acyclic subunits (rule 3) and the higherseniority of a subunit with lower locant(s) relative to the same subunit with higher locant(s)

(rule 7b) yield the CRU XVI with the name poly(cyelohexane-I ,3-diylcyclohexane-1 l-methylpropane- L3-diyl) Note that all acyclic subunits exeept CH2 and CH2CH2 arenamed as alkane-ex, co-diyl CH2 and CH2CH2 subunits are named methylene and ethylene,

,4-diyl-respectively

In the IUPAC system locants are placed immediately before the part of the name to whichthey apply; for instance subunits such as pyridine-2,4-diyl and l-methylpropane-I,3-diyl.One of the few exceptions is the phenylene subunit, for example, 1,4-phenylene in Xv.

The IUPAC nomenclature system is always evolving and some of the details (e.g., the names

of some subunits) have changed in recent years One should use caution when using lessrecent nomenclature references than those listed in this text

The IUPAC nomenclature system recognizes that most of the common (commercial)polymers have source-based or semisystematie names that are well established by usage.IPUAC does not intend that such names be supplanted by the IUPAC names but anticipatesthat such names will be kept to a minimum The IUPAC system is generally used for allexcept the common polymers The IUPAC names for various of the common polymers areindicated below the more established source or semi systematic name in the following:

Thc IUPAC nomenclature will be used in this book with some exceptions One exception

is the use of well-established, non-IUPAC names for most of the commonly encounteredpolymers of commercial importance Another exception will be in not following rule 2 forwriting the constitutional repeating unit (although the correct IUPAC name will beemployed) Using the IUPAC choice of the CRU leads in some cases to structurcs that arelonger and appear more complicated Thus the IUPAC structure for the polymer in Eq 1-3 is

although both XXVI and XXVII denote the exact same structure This type of problem arises

only with certain polymers and then only when the drawn structure is to include the cnds ofthe polymer chain instcad of simply the repeating unit or the CRU The CRU will also gen-crally not be used in equations such as Eq 1-9 The polymerization mechanism in such reac-tions involves the propagating center on the substituted carbon atom of the monomer Using

Equation 1-9 has the repeating unit written the same way on both sides, while Eq 1-14 hasthe repeating unit reversed on the right side relative to what it is on the left side.

Before proceeding one needs to mention Chemical Ahstracts (CA), a journal published by

the American Chemical Society, that abstracts the world's chemical literature and has oped its own nomenclature rules The CA rules are generally very close to the IUPAC rules,but there are some differences Most of the differences are not important at the level of thediscussions in this book One difference that needs to be mentioned is the placement oflocants CA does not place locants immediately before the part of the name to which they

devel-apply Thus, the CA name for the first subunit in XV is 2,4-pyridinediyl instead of 2,4-diyl The difference between IUPAC and CA is also seen in the placement of locants innaming vinyl monomers such as CH2=CHCH2CH3. The IUPAC name is but-I-ene; the CAname is I-butene Most chemists tend to follow the CA placement of locants for small mole-cules This text will generally follow the IUPAC rule for locants for CRU subunits, but the

pyridine-CA rule for monomers

1-2d Trade Names and Nonnames

Special terminology based on trade names has been employed for some polymers Althoughtrade names should be avoided, one must be familiar with those that are firmly establishedand commonly used An example of trade-name nomenclature is the use of the name nylonfor the polyamides from unsubstituted, nonbranched aliphatic monomers Two numbers areadded onto the word "nylon" with the first number indicating the number of methylenegroups in the diamine portion of the polyamide and the second number the number of carbonatoms in the diacyl portion Thus poly(hexamethylene adipamide) and poly(hexamethylenesebacamide) are nylon 6,6 and nylon 6,10, respectively Variants of these names arefrequently employed The literature contains such variations of nylon 6,6 as nylon 66, 66nylon, nylon 6/6, 6,6 nylon, and 6-6 nylon Polyamides from single monomers are denoted

by a single number to denote the number of carbon atoms in the repeating unit caprolactam) or poly(6-aminocaproic acid) is nylon 6

PolY(E-In far too many instances trade-name polymer nomenclature conveys very little meaningregarding the structure of a polymer Many condensation polymers, in fact, seem not to havenames Thus the polymer obtained by the step polymerization of formaldehyde and phenol is

variously referred to a phenol-formaldehyde polymer, phenol-formaldehyde resin, phenolic,phenolic resin, and phenoplast Polymers of formaldehyde or other aldehydes with urea or

melamine are generally referred to as amino resins or aminoplasts without any more specific

names It is often extremely difficult to determine which aldehyde and which amino

mono-mers have been used to synthesize a particular polymer being referred to as an amino resin.

More specific nomenclature, if it can be called that, is afforded by indicating the two tants as in names such as urea-formaldehyde resin or melamine-formaldehyde resin

reac-A similar situation exists with the naming of many other polymers Thus the polymer

XXVII is usually referred to as "the polycarbonate from bisphenol A" or polycarhonate. The

linear polymers. Under certain reaction conditions or with certain kinds of monomers thepolymers can be quite different.

Branched polymers polymers with more than two chain ends per molecule, can form inboth step and chain polymerizations Branched polymer molecules are those in which thereare side branches of linked monomer molecules protruding from various central branchpoints along the main polymer chain The difference between the shapes of linear andbranched polymer molecules can be seen from the structural representations in Fig 1-2.The branch points are indicated by heavy dots The illustrations show that there are severaldifferent kinds of branched polymers The branched polymer can be comblike in structurewith either long (A) or short (B) branches When there is extensive branching, the polymercan have a dendritic structure in which there are branches protruding from other branches,that is, branched branches (C) The presence of branching in a polymer usually has a largeeffect on many important polymer properties The most significant property change broughtabout by branching is the decrease in crystallinity Branched polymers do not pack as easilyinto a crystal lattice as do linear polymers

It is important to point out that the term branched polymer does not refer to linear

poly-mers containing side groups that are part of the monomer structure Only those polypoly-mers that

contain side branches composed of complete monomer units are termed branched polymers.

Thus polystyrene XXVIII is classified as a linear polymer, and not as a branched polymer,

When polymers are produced in which the polymer molecules are linked to each other at

points other than their ends, the polymers are said to be crosslinked (Fig 1-2) Crosslinking

can be made to occur during the polymerization process by the use of appropriate monomers

It can also be brought about after the polymerization by various chemical reactions Thecrosslinks between polymer chains can be of different lengths depending on the crosslinkingmethod and the specific conditions employed One can also vary the number of crosslinks so

as to obtain lightly or highly crosslinked polymers When the number of crosslinks is

suffi-ciently high, a three-dimensional or space network polymer is produced in which all thepolymer chains in a sample have been linked together to form one giant molecule Lightcrosslinking is used to impart good recovery (elastic) properties to polymers to be used asrubbers High degrees of crosslinking are used to impart high rigidity and dimensional sta-bility (under conditions of heat and stress) to polymers such as the phenol-formaldehyde andurea~formaldehyde polymers

1-4 MOLECULAR WEIGHT

The molecular weight of a polymer is of prime importance in the polymer's synthesis and

application Chemists usually use the term molecular weight to describe the size of a

mole-cule The more accurate term is molar mass, usually in units of g mol-I The term molecularweight is the ratio of the average mass per formula unit of a substance to nth of the mass of

an atom of 12C and is dimensionless (lUPAC, 1991, in press) This text will use molecular

term for most chemists

The interesting and useful mechanical properties that are uniquely associated with meric materials are a consequence of their high molecular weight Most important mechan-ical properties depend on and vary considerably with molecular weight as seen in Fig 1-3.There is a minimum polymer molecular weight (A), usually a thousand or so to produce anysignificant mechanical strength at all Above A, strength increases rapidly with molecularweight until a critical point (B) is reached Mechanical strength increases more slowly above

poly-B and eventually reaches a limiting value (C) The critical point poly-B generally corresponds tothe minimum molecular weight for a polymer to begin to exhibit sufficient strength to beuseful Most practical applications of polymers require higher molecular weights to obtainhigher strengths The minimum useful molecular weight (B), usually in the range 5000-10,000, differs for different polymers The plot in Fig 1-3 generally shifts to the right

as the magnitude of the intermolecular forces decreases Polymer chains with stronger