FUNDAMENTALS OF POLYMER ENGINEERING doc

FUNDAMENTALS
OF
Second
Edition
Revised
and
Expanded
Anil
Kumar
Indian
Institute
of
Technology
Kanpur,
India
Rakesh
K.
Gupta
West
Virginia University
Morgantown,
West
Virginia,
U.S.A.
MARCEL
MARCEL
DEKKER,
INC.
NEW
YORK
•

BASEL
Copyright © 2003 Marcel Dekker, Inc.
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ISBN: 0-8247-0867-9
The first edition was published as Fundamentals of Polymers by McGraw-Hill, 1997.
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Copyright © 2003 Marcel Dekker, Inc.
PLASTICS

ENGINEERING
Founding
Editor
Donald
E.
Hudgin
Professor
Clemson
University
Clemson,
South Carolina
1.
Plastics Waste Recovery
of
Economic Value, Jacob Letdner
2
Polyester Molding Compounds, Robert Burns
3
Carbon Black-Polymer Composites
The
Physics
of
Electrically Conducting
Composites, edited
by
Enid
Keil
Sichel
4
The

Strength
and
Stiffness
of
Polymers, edited
byAnagnostis
£
Zachanades
and
RogerS
Porter
5
Selecting Thermoplastics
for
Engineering Applications, Charles
P
Mac-
Dermott
6
Engineering
with
Rigid
PVC
Processabihty
and
Applications, edited
by I
Luis
Gomez
7

Computer-Aided
Design
of
Polymers
and
Composites,
D H
Kaelble
8
Engineering Thermoplastics Properties
and
Applications, edited
by
James
M
Margolis
9
Structural Foam
A
Purchasing
and
Design Guide,
Bruce
C
Wendle
10
Plastics
in
Architecture
A

Guide
to
Acrylic
and
Polycarbonate, Ralph
Montella
11
Metal-Filled
Polymers
Properties
and
Applications,
edited
by
Swapan
K
Bhattacharya
12
Plastics Technology Handbook, Manas
Chanda
and
Salil
K Roy
13
Reaction Injection Molding Machinery
and
Processes,
F
Melvin
Sweeney

14
Practical
Thermoforming
Principles
and
Applications, John
Flonan
15
Injection
and
Compression Molding Fundamentals, edited
by
Avraam
I
Isayev
16
Polymer Mixing
and
Extrusion Technology, Nicholas
P
Cheremismoff
17
High
Modulus Polymers Approaches
to
Design
and
Development, edited
by
Anagnostis

E
Zachanades
and
Roger
S
Porter
18
Corrosion-Resistant Plastic Composites
in
Chemical Plant Design, John
H
Mallinson
19
Handbook
of
Elastomers
New
Developments
and
Technology, edited
by
Anil
K
Bhowmick
and
Howard
L
Stephens
20
Rubber Compounding Principles, Materials,

and
Techniques, Fred
W
Barlow
21
Thermoplastic Polymer Additives Theory
and
Practice, edited
by
John
T
Lutz,
Jr
22
Emulsion Polymer Technology, Robert
D
Athey,
Jr
23
Mixing
in
Polymer Processing, edited
by
Chns
Rauwendaal
24
Handbook
of
Polymer Synthesis, Parts
A and B,

edited
by
Hans
R
Kncheldorf
Copyright © 2003 Marcel Dekker, Inc.
25.
Computational
Modeling
of
Polymers,
edited
by
Jozef
Bicerano
26.
Plastics Technology Handbook: Second Edition, Revised
and
Expanded,
Manas
Chanda
and
Salil
K.
Roy
27.
Prediction
of
Polymer Properties,
Jozef Bicerano

28.
Ferroelectric Polymers: Chemistry, Physics,
and
Applications,
edited
by
Hari
Singh
Nalwa
29.
Degradable
Polymers,
Recycling,
and
Plastics
Waste
Management,
edited
by
Ann-Christine
Albertsson
and
Samuel
J.
Huang
30.
Polymer
Toughening,
edited
by

Charles
B.
Arends
31.
Handbook
of
Applied
Polymer Processing Technology,
edited
by
Nicholas
P.
Cheremisinoff
and
Paul
N.
Cheremisinoff
32.
Diffusion
in
Polymers,
edited
by P.
Neogi
33.
Polymer Devolatilization,
edited
by
Ramon
J.

Albalak
34.
Anionic Polymerization: Principles
and
Practical Applications,
Henry
L.
Hsieh
and
Roderic
P.
Quirk
35.
Cationic Polymerizations: Mechanisms, Synthesis,
and
Applications,
edited
by
Krzysztof
Matyjaszewski
36.
Polyimides: Fundamentals
and
Applications,
edited
by
Malay
K.
Ghosh
and

K.
L.
Mittal
37.
Thermoplastic Melt Rheology
and
Processing,
A. V.
Shenoy
and D. R.
Saini
38.
Prediction
of
Polymer Properties: Second Edition, Revised
and
Expanded,
Jozef Bicerano
39.
Practical Thermoforming: Principles
and
Applications, Second Edition,
Revised
and
Expanded,
John
Florian
40.
Macromolecular
Design

of
Polymeric Materials,
edited
by
Koichi
Hatada,
Tatsuki
Kitayama,
and
Otto
Vogl
41.
Handbook
of
Thermoplastics,
edited
by
Olagoke Olabisi
42.
Selecting Thermoplastics
for
Engineering Applications: Second Edition,
Revised
and
Expanded,
Charles
P.
MacDermott
and
Aroon

V.
Shenoy
43.
Metallized Plastics: Fundamentals
and
Applications,
edited
by K. L
Mittal
44.
Oligomer Technology
and
Applications,
Constantin
V.
Uglea
45.
Electrical
and
Optical Polymer Systems: Fundamentals, Methods,
and
Applications,
edited
by
Donald
L.
Wise,
Gary
E.
Wnek, Debra

J.
Trantolo,
Thomas
M.
Cooper,
and
Joseph
D.
Gresser
46.
Structure
and
Properties
of
Multiphase Polymeric Materials,
edited
by
Takeo
Araki,
Qui
Tran-Cong,
and
Mitsuhiro Shibayama
47.
Plastics Technology Handbook: Third Edition, Revised
and
Expanded,
Manas Chanda
and
Salil

K. Roy
48.
Handbook
of
Radical Vinyl Polymerization,
Munmaya
K.
Mishra
and
Yusuf
Yagci
49.
Photonic Polymer Systems: Fundamentals, Methods,
and
Applications,
edited
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L
Wise,
Gary
E.
Wnek, Debra
J.
Trantolo, Thomas
M.
Cooper,
and
Joseph
D.

Gresser
50.
Handbook
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Polymer Testing: Physical Methods,
edited
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Roger Brown
51.
Handbook
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Polypropylene
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Polypropylene
Composites,
edited
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Har-
utun
G.
Karian
52.
Polymer Blends
and
Alloys,
edited
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Gabriel
O.
Shonaike

and
George
P.
Simon
53.
Star
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Hyperbranched Polymers,
edited
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Munmaya
K.
Mishra
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Shi-
ro
Kobayashi
54.
Practical Extrusion Blow Molding,
edited
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Samuel
L.
Belcher
Copyright © 2003 Marcel Dekker, Inc.
55
Polymer
Viscoelasticity
Stress
and

Strain
in
Practice,
Evaristo
Riande,
Ricardo
Diaz-Calleja,
Margarita
G
Prolongo, Rosa
M
Masegosa,
and
Cat-
alma
Salom
56
Handbook
of
Polycarbonate Science
and
Technology, edited
by
Donald
G
LeGrand
and
John
T
Bendler

57
Handbook
of
Polyethylene Structures, Properties,
and
Applications, Andrew
J
Peacock
58
Polymer
and
Composite
Rheology
Second
Edition,
Revised
and
Expanded,
Rakesh
K
Gupta
59
Handbook
of
Polyolefms
Second
Edition
Revised
and
Expanded, edited

by
Cornelia
Vasile
60
Polymer Modification
Principles,
Techniques,
and
Applications, edited
by
John
J
Meister
61
Handbook
of
Elastomers Second Edition, Revised
and
Expanded, edited
by
Anil
K
Bhowmick
and
Howard
L
Stephens
62
Polymer Modifiers
and

Additives,
edited
by
John
T
Lutz,
Jr,
and
Richard
F
Grossman
63
Practical Injection Molding,
Bernie
A
Olmstea
and
Martin
E
Davis
64
Thermosetting
Polymers, Jean-Pierre
Pascault,
Henry
Sautereau,
Jacques
Verdu,
and
Roberto

J J
Williams
65
Prediction
of
Polymer Properties Third Edition, Revised
and
Expanded, Jozef
Bicerano
66
Fundamentals
of
Polymer Engineering Second Edition, Revised
and
Expanded,
Anil
Kumar
and
Rakesh
K
Gupta
Additional Volumes
in
Preparation
Handbook
of
Plastics Analysis, edited
by
Hubert Lobo
and

Jose
Bonilla
Metallocene Catalysts
in
Plastics Technology, Anand Kumar
Kulshreshtha
Copyright © 2003 Marcel Dekker, Inc.
To the memor y of my father.
Anil Kumar
To the memor y of my father.
Rakesh Gupta
Copyright © 2003 Marcel Dekker, Inc.
Preface to the Second Edition
The objectives and organization of the second edition remain essentially
unchanged. The major difference from the first edition is the inclusion of
new material on topics such as dendrimers, polymer recycling, Hansen
solubility parameters, nanocomposites, creep in glassy polymers, and twin-
screw extrusion. New examples have been introduced throughout the book,
additional problems appear at the end of each chapter, and references to the
literature have been updated. Additional text and figures have also been added.
The first edition has been successfully used in universities around the
world, and we have received many encouraging comments. We hope the
second edition will also find favor with our colleagues, and be useful to future
generations of students of polymer science and engineering.
Anil Kumar
Rakesh K. Gupta
v
Copyright © 2003 Marcel Dekker, Inc.
Preface to the First Edition
Synthetic polymers have considerable commercial importance and are known

by several common names, such as plastics, macromolecules, and resins.
These materials have become such an integral part of our daily existence that
an introductory polymer course is now included in the curriculum of most
students of science and engineering. We have written this book as the main
text for an introductory course on polymers for advanced undergraduates and
graduate students. The intent is to provide a systematic coverage of the
essentials of polymers.
After an introduction to polymers as materials in the first two chapters,
the mechanisms of polymerization and their effect on the engineering design
of reactors are elucidated. The succeeding chapters consider polymer char-
acterization, polymer thermodyn amics, and the behavior of polymers as
melts, solution s, and solids both above and below the glass transition
temperature. Also examined are crystallization, diffusion of and through
polymers, and polymer processing. Each chapter can, for the most part, be
vii
Copyright © 2003 Marcel Dekker, Inc.
read independently of the others, and this should allow an instructor to design
the course to his or her own liking. Note that the problems given at the end of
each chapter also serve to complement the main text. Some of these problems
cite references to the literature where alternative viewpoints are introduced. We
have been teaching polymer science for a long time, and we have changed the
course content from year to year by adopting and expanding on ideas of the
kind embodied in these problems.
Since polymer science is an extremely vast area, the decision to include
or exclude a given subject matter in the text has been a difficult one. In this
endeavor, although our own biases will show in places, we have been guided
by how indispens able a particular topic is to proper understanding. We have
attempted to keep the treatment simple without losing the essential features;
for depth of coverage, the reader is referred to the pertinent technical literature.
Keeping the student in mind, we have provided intermediate steps in most

derivations. For the instructor, lecturing becomes easy since all that is
contained in the book can be put on the board. The future will tell to what
extent we have succeeded in our chosen objectives.
We have benefited from the comments of several friends and colleagues
who read different parts of the book in draft form. Our special thanks go to
Ashok Khanna, Raj Chhabra, Deepak Doraiswamy, Hota V. S. GangaRao,
Dave Kofke, Mike Ryan, and Joe Shaeiwitz. Professor Khanna has used the
problem sets of the first seven chapters in his class for several years.
After finishing my Ph.D. from Carnegie-Mellon University, I (Anil
Kumar) joined the Department of Chemical Engineering at the Indian Institute
of Technology, Kanpur, India, in 1972. My experience at this place has been
rich and complete, and I decided to stay here for the rest of my life. I am
fortunate to have a good set of students from year to year with whom I have
been able to experiment in teaching various facets of polymer science and
modify portions of this book continuously.
Rakesh Gupta would like to thank Professor Santosh Gupta for introdu-
cing polymer science to him when he was an undergraduate student. This
interest in polymers was nurtured by Professor Art Metzner and Dr. K. F.
Wissbrun, who were his Ph.D. thesis advisors. Rakesh learned even more from
the many graduate students who chose to work with him, and their contribu-
tions to this book are obvious. Kurt Wissbrun reviewed the entire manuscript
and provided invaluable help and encouragement during the final phases of
writing. Progress on the book was also aided by the enthusiastic support of
Gene Cilento, the Department Chairman at West Virginia University. Rakesh
adds that these efforts would have come to nought without the determined help
of his wife, Gunjan, who guarded his spare time and allowed him to devote it
viii Preface to the First Edition
Copyright © 2003 Marcel Dekker, Inc.
entirely to this project. According to Rakesh, ‘‘She believed me when I told
her it would take two years; seven years later she still believes me!’’

I doubt that this book would ever have been completed without the
constant support of my wife, Renu. During this time there have been several
anxious moments, primarily because our children, Chetna and Pushkar, were
trying to choose their careers and settle down. In taking care of them, my role
was merely helping her, and she allowed me to divide my attention between
home and work. Thank you, Renu.
Anil Kumar
Rakesh Gupta
Preface to the First Edition ix
Copyright © 2003 Marcel Dekker, Inc.
Contents
PrefacetotheSecondEditionv
PrefacetotheFirstEditionvii
1.Introduction1
1.1DefiningPolymers1
1.2ClassificationofPolymersandSomeFundamental
Concepts4
1.3ChemicalClassificationofPolymersBasedon
PolymerizationMechanisms16
1.4Molecular-WeightDistributions19
1.5ConfigurationsandCrystallinityofPolymericMaterials22
1.6ConformationofPolymerMolecules27
1.7PolymericSupportsinOrganicSynthesis29
1.8Conclusion38
xi
Copyright © 2003 Marcel Dekker, Inc.
References39
Problems39
2.EffectofChemicalStructureonPolymerProperties45
2.1Introduction45

2.2EffectofTemperatureonPolymers45
2.3AdditivesforPlastics50
2.4Rubbers61
2.5CellulosePlastics66
2.6CopolymersandBlends68
2.7Cross-LinkingReactions72
2.8Ion-ExchangeResins80
2.9Conclusion89
References90
Problems91
3.Step-GrowthPolymerization103
3.1Introduction103
3.2EsterificationofHomologousSeriesandtheEqual
ReactivityHypothesis105
3.3KineticsofA–R–BPolymerizationUsingEqual
ReactivityHypothesis107
3.4AverageMolecularWeightinStep-GrowthPolymerization
ofARBMonomers111
3.5EquilibriumStep-GrowthPolymerization116
3.6Molecular-WeightDistributioninStep-Growth
Polymerization118
3.7ExperimentalResults125
3.8Conclusion140
Appendix3.1:TheSolutionofMWDThroughthe
GeneratingFunctionTechniqueinStep-Growth
Polymerization140
References143
Problems145
4.ReactionEngineeringofStep-GrowthPolymerization153
4.1Introduction153

xii Contents
Copyright © 2003 Marcel Dekker, Inc.
4.2AnalysisofSemibatchReactors156
4.3MWDofARBPolymerizationinHomogeneous
Continuous-FlowStirred-TankReactors166
4.4AdvancedStageofPolymerization169
4.5Conclusion174
Appendix4.1:SimilaritySolutionofStep-Growth
PolymerizationinFilmswithFiniteMassTransfer175
References181
Problems181
5.Chain-GrowthPolymerization188
5.1Introduction188
5.2RadicalPolymerization192
5.3KineticModelofRadicalPolymerization197
5.4AverageMolecularWeightinRadicalPolymerization199
5.5VerificationoftheKineticModelandtheGelEffect
inRadicalPolymerization201
5.6EquilibriumofRadicalPolymerization210
5.7TemperatureEffectsinRadicalPolymerization215
5.8IonicPolymerization216
5.9AnionicPolymerization222
5.10Ziegler-NattaCatalystsinStereoregularPolymerization226
5.11KineticMechanisminHeterogeneousStereoregular
Polymerization230
5.12StereoregulationbyZiegler-NattaCatalyst232
5.13RatesofZiegler-NattaPolymerization233
5.14AverageChainLengthofthePolymerinStereoregular
Polymerization238
5.15DiffusionalEffectinZiegler-NattaPolymerization240

5.16NewerMetalloceneCatalystsforOlefinPolymerization242
5.17Conclusion244
References244
Problems248
6.ReactionEngineeringofChain-GrowthPolymerization255
6.1Introduction255
6.2DesignofTubularReactors256
6.3Copolymerization273
Contents xiii
Copyright © 2003 Marcel Dekker, Inc.
6.4RecyclingandDegradationofPolymers285
6.5Conclusion287
Appendix6.1:SolutionofEquationsDescribing
IsothermalRadicalPolymerization287
References293
Problems294
7.EmulsionPolymerization299
7.1Introduction299
7.2AqueousEmulsifierSolutions300
7.3SmithandEwartTheoryforStateIIofEmulsion
Polymerization304
7.4EstimationoftheTotalNumberofParticles,N
t
313
7.5MonomerConcentrationinPolymerParticles,[M]315
7.6DeterminationofMolecularWeightinEmulsion
Polymerization319
7.7EmulsionPolymerizationinHomogeneous
Continuous-FlowStirred-TankReactors324
7.8Time-DependentEmulsionPolymerization326

7.9Conclusions334
References335
Problems336
8.MeasurementofMolecularWeightandItsDistribution340
8.1Introduction340
8.2End-GroupAnalysis342
8.3ColligativeProperties343
8.4LightScattering350
8.5Ultracentrifugation354
8.6IntrinsicViscosity358
8.7GelPermeationChromatography364
8.8Conclusion369
References369
Problems371
9.ThermodynamicsofPolymerMixtures374
9.1Introduction374
xiv Contents
Copyright © 2003 Marcel Dekker, Inc.
9.2CriteriaforPolymerSolubility376
9.3TheFlory-HugginsTheory379
9.4Free-VolumeTheories396
9.5TheSolubilityParameter398
9.6PolymerBlends401
9.7Conclusion403
References403
Problems405
10.TheoryofRubberElasticity407
10.1Introduction407
10.2ProbabilityDistributionfortheFreelyJointedChain408
10.3ElasticForceBetweenChainEnds415

10.4Stress-StrainBehavior418
10.5TheStressTensor(Matrix)420
10.6MeasuresofFiniteStrain423
10.7TheStressConstitutiveEquation427
10.8VulcanizationofRubberandSwellingEquilibrium429
10.9Conclusion432
References433
Problems434
11.PolymerCrystallization437
11.1Introduction437
11.2EnergeticsofPhaseChange443
11.3OverallCrystallizationRate447
11.4EmpiricalRateExpressions:TheAvramiEquation450
11.5PolymerCrystallizationinBlendsandComposites456
11.6MeltingofCrystals459
11.7InfluenceofPolymerChainExtensionandOrientation462
11.8PolymerswithLiquid-CrystallineOrder464
11.9StructureDetermination467
11.10WorkingwithSemicrystallinePolymers479
11.11Conclusion480
References481
Problems484
Contentsxv
Copyright © 2003 Marcel Dekker, Inc.
12.MechanicalProperties487
12.1Introduction487
12.2Stress-StrainBehavior488
12.3TheGlassTransitionTemperature497
12.4DynamicMechanicalExperiments501
12.5Time-TemperatureSuperposition504

12.6PolymerFracture508
12.7CrazingandShearYielding511
12.8FatigueFailure516
12.9ImprovingMechanicalProperties518
References520
Problems523
13.PolymerDiffusion526
13.1Introduction526
13.2FundamentalsofMassTransfer527
13.3DiffusionCoefficientMeasurement531
13.4DiffusivityofSpheresatInfiniteDilution542
13.5DiffusionCoefficientforNon-ThetaSolutions546
13.6Free-VolumeTheoryofDiffusioninRubberyPolymers547
13.7GasDiffusioninGlassyPolymers552
13.8OrganicVaporDiffusioninGlassyPolymers:
CaseIIDiffusion557
13.9Polymer-PolymerDiffusion560
13.10Conclusion564
References565
Problems569
14.FlowBehaviorofPolymericFluids573
14.1Introduction573
14.2ViscometricFlows576
14.3Cone-and-PlateViscometer578
14.4TheCapillaryViscometer584
14.5ExtensionalViscometers589
14.6BoltzmannSuperpositionPrinciple592
14.7DynamicMechanicalProperties595
14.8TheoriesofShearViscosity598
xvi Contents

Copyright © 2003 Marcel Dekker, Inc.
14.9ConstitutiveBehaviorofDilutePolymerSolutions605
14.10ConstitutiveBehaviorofConcentratedSolutionsand
Melts615
14.11Conclusion622
References622
Problems626
15.PolymerProcessing630
15.1Introduction630
15.2Extrusion631
15.3InjectionMolding651
15.4FiberSpinning667
15.5Conclusion680
References680
Problems684
Contents xvii
Copyright © 2003 Marcel Dekker, Inc.
1
Introduction
1.1 DEFINING POLYMERS
Polymers are materials of very high molecular weight that are found to have
multifarious applications in our modern society. They usually consist of several
structural units bound together by covalent bonds [1,2]. For example, polyethy-
lene is a long-chain polymer and is represented by
ÀCH
2
CH
2
CH
2

À or ½ÀCH
2
CH
2
À
n
ð1:1:1Þ
where the structural (or repeat) unit is ÀCH
2
ÀCH
2
À and n represents the chain
length of the polymer.
Polymers are obtained through the chemical reaction of small molecular
compounds called monomers. For example, polyethylene in Eq. (1.1.1) is formed
from the monomer ethylene. In order to form polymers, monomers either have
reactive functional groups or double (or triple) bonds whose reaction provides the
necessary linkages between repeat units. Polymeric materials usually have high
strength, possess a glass transition temperature, exhibit rubber elasticity, and have
high viscosity as melts and solutions.
In fact, exploitation of many of these unique properties has made polymers
extremely useful to mankind. They are used extensively in food packaging,
clothing, home furnishing, transportation, medical devices, information technol-
ogy, and so forth. Natural fibers such as silk, wool, and cotton are polymers and
1
Copyright © 2003 Marcel Dekker, Inc.
TABLE 1.1 Some Common Polymers
Commodity thermoplastics
Polyethylene
Polystyrene

Polypropylene
Polyvinyl chloride
Polymers in electronic applications
Polyacetylene
Poly(p-phenylene vinylene)
Polythiophene
Polyphenylene sulfide
Polyanilines
Biomedical applications
Polycarbonate (diphenyl carbonate)
Polymethyl methacrylate
Silicone polymers
2Chapter1
Copyright © 2003 Marcel Dekker, Inc.
havebeenusedforthousandsofyears.Withinthiscentury,theyhavebeen
supplementedand,insomeinstances,replacedbysyntheticfiberssuchasrayon,
nylon,andacrylics.Indeed,rayonitselfisamodificationofanaturallyoccurring
polymer,cellulose,whichinothermodifiedformshaveservedforyearsas
commercialplasticsandfilms.Syntheticpolymers(somecommononesarelisted
inTable1.1)suchaspolyolefins,polyesters,acrylics,nylons,andepoxyresins
find extensive applications as plastics, films, adhesives, and protective coatings. It
may be added that biological materials such as proteins, deoxyribonucleic acid
(DNA), and mucopolysaccharides are also polymers. Polymers are worth study-
ing because their behavior as materials is different from that of metals and other
low-molecular-weight materials. As a result, a large percentage of chemists and
engineers are engaged in work involving polymers, which necessitates a formal
course in polymer science.
Biomaterials [3] are defined as materials used within human bodies either
as artificial organs, bone cements, dental cements, ligaments, pacemakers, or
contact lenses. The human body consists of biological tissues (e.g., blood, cell,

proteins, etc.) and they have the ability to reject materials which are ‘‘incompa-
tible’’ either with the blood or with the tissues. For such applications, polymeric
materials, which are derived from animals or plants, are natural candidates and
some of these are cellulosics, chitin (or chitosan), dextran, agarose, and collagen.
Among synthetic materials, polysiloxane, polyurethane, polymethyl methacry-
Specialty polymers
Polyvinylidene chloride
Polyindene
Polyvinyl pyrrolidone
Coumarone polymer
Introduction 3
Copyright © 2003 Marcel Dekker, Inc.
late, polyacrylamide, polyester, and polyethylene oxides are commonly employed
because they are inert within the body. Sometimes, due to the requirements of
mechanical strength, selective permeation, adhesion, and=or degradation, even
noncompatible polymeric materials have been put to use, but before they are
utilized, they are surface modified by biological molecules (such as, heparin,
biological receptors, enzymes, and so forth). Some of these concepts will be
developed in this and subsequent chapters.
This chapter will mainly focus on the classification of polymers; subse-
quent chapters deal with engineering problems of manufacturing, characteriza-
tion, and the behavior of polymer solutions, melts, and solids.
1.2 CLASSIFICATION OF POLYMERS AND SOME
FUNDAMENTAL CONCEPTS
One of the oldest ways of classifying polymers is based on their response to heat.
In this system, there are two types of polymers: thermoplastics and thermosets. In
the former, polymers ‘‘melt’’ on heating and solidify on cooling. The heating and
cooling cycles can be applied several times without affecting the properties.
Thermoset polymers, on the other hand, melt only the first time they are heated.
During the initial heating, the polymer is ‘‘cured’’; thereafter, it does not melt on

reheating, but degrades.
A more important classification of polymers is based on molecular
structure. According to this system, the polymer could be one of the following:
1. Linear-chain polymer
2. Branched-chain polymer
3. Network or gel polymer
It has already been observed that, in order to form polymers, monomers must
have reactive functional groups, or double or triple bonds. The functionality of a
given monomer is defined to be the number of these functional groups; double
bonds are regarded as equivalent to a functionality of 2, whereas a triple bond has
a functionality of 4. In order to form a polymer, the monomer must be at least
bifunctional; when it is bifunctional, the polymer chains are always linear. It is
pointed out that all thermoplastic polymers are essentially linear molecules,
which can be understood as follows.
In linear chains, the repeat units are held by strong covalent bonds, while
different molecules are held together by weaker secondary forces. When thermal
energy is supplied to the polymer, it increases the random motion of the
molecules, which tries to overcome the secondary forces. When all forces are
overcome, the molecules become free to move around and the polymer melts,
which explains the thermoplastic natur e of polymers.
4Chapter1
Copyright © 2003 Marcel Dekker, Inc.
Branched polymers contain molecules having a linear backbone with
branches emanating randomly from it. In order to form this class of material,
the monomer must have a capability of growing in more than two directions,
which implies that the starting monomer must have a functionality greater than 2.
For example, consider the polymerization of phthalic anhydride with glycerol,
where the latter is tri-functional:
C
O

C
O
O
CH
OH
CH
2
OH +
CH
CH
2
O
OH
C
O
C
O
OCH
2
C
O
C
O
O
CH CH
2
(1.2.1)
CH
2
OH

CH
2
OH
The branched chains shown are formed only for low conversions of monomers.
This implies that the polymer formed in Eq. (1.2.1) is definitely of low molecular
weight. In order to form branched polymers of high molecular weight, we must
use special techniques, which will be discussed later. If allowed to react up to
large conversions in Eq. (1.2.1), the polymer becomes a three-dimensional
network called a gel, as follows:
OC
O
C
O
CH
2
CH
CH
2
O
O
O
CO
C
O
O
OC
O
C
O
CH

2
CH
CH
2
OO
CH
2
CH CH
2
OC
O
C
O
CH
2
CH CH
2
OC
O
C
O
(1.2.2)
O
CO
C
O
O
Introduction 5
Copyright © 2003 Marcel Dekker, Inc.
In fact, whenever a multifunctional monomer is polymerized, the polymer evolves

through a collection of linear chains to a collection of branched chains, which
ultimately forms a network (or a gel) polymer. Evidently, the gel polymer does
not dissolve in any solvent, but it swells by incorporating molecules of the solvent
into its own matrix.
Generally, any chemical process can be subdivided into three stages [viz.
chemical reaction, separation (or purification) and identification]. Among the
three stages, the most difficult in terms of time and resources is separation. We
will discuss in Section 1.7 that polymer gels have gained considerable importance
in heterogeneous catalysis because it does not dissolve in any medium and the
separation step reduces to the simple removal of various reacting fluids. In recent
times, a new phase called the fluorous phase, has been discovered which is
immiscible to both organic and aqueous phases [4,5]. However, due to the high
costs of their synthesis, they are, at present, only a laboratory curiosity. This
approach is conceptually similar to solid-phase separation, except that fluorous
materials are in liquid state.
In dendrimer separation, the substrates are chemically attached to the
branches of the hyper branched polymer (called dendrimers). In these polymers,
(A) CH
2
CHCO
2
Me
(B) NH
2
CH
2
CH
2
NH
2

(Excess)
Repeat steps (A) and (B)
NH
2
N
N
N
NH
2
N
H
2
NNH
2
NH
2
H
2
N
(Generation = 1.0) (etc)
(Generation = 0)
N
N
N
N
N
N
NN
NN
H

2
N
H
2
NNH
2
NH
2
NH
2
NH
2
NH
2
NH
2
H
2
N
H
2
N
H
2
N
H
2
N
Terminal
groups

Initiator
core
‘Dendrimers’
Generations
Dendrimer
repeating units
0
1
2
(1.2.3a)
N
NHC
CNH
CNH
O
O
O
NH
2
H
2
N
NH
2
H
2
N
N
NH
2

NH
2
NH
3
6Chapter1
Copyright © 2003 Marcel Dekker, Inc.
the extent of branching is controlled to make them barely soluble in the reaction
medium. Dendrimers [6] possess a globular structure characterized by a central
core, branching units, and terminal units. They are prepared by repetitive reaction
steps from a central initiator core, with each subsequent growth creating a new
generation of polymers. Synthesis of polyamidoamine (PAMAM) dendrimers are
done by reacting acrylamide with core ammonia in the presence of excess
ethylene diamine.
Dendrimers have a hollow interior and densely packed surfaces. They have
a high degree of molecular uniformity and shape. These have been used as
membrane materials and as filters for calibrating analytical instruments, and
newer paints based on it give better bonding capacity and wear resistance. Its
sticking nature has given rise to newer adhesives and they have been used as
catalysts for rate enhancement. Environmental pollution control is the other field
in which dendrimers have found utility. A new class of chemical sensors based on
these molecules have been developed for detection of a variety of volatile organic
pollutants.
In all cases, when the polymer is examined at the molecular level, it is
found to consist of covalently bonded chains made up of one or more repeat units.
The name given to any polymer species usually depends on the chemical structur e
of the repeating groups and does not reflect the details of structure (i.e., linear
molecule, gel, etc.). For example, polystyrene is formed from chains of the repeat
unit:
CH
CH

2
(1.2.3b)
Such a polymer derives it name from the monomer from which it is usually
manufactured. An idealized sample of polymer would consist of chains all having
identical molecular weight. Such systems are called monodisperse polymers.In
practice, however, all polymers are made up of molecules with molecular weights
that vary over a range of values (i.e., have a distribution of molecular weights)
and are said to be polydisperse. Whether monodisperse or polydisperse, the
chemical formula of the polymer remains the same. For example, if the polymer
is polystyrene, it would continue to be represented by
CH
2
CH
n
CH
CH
2
XCH
2
CH Y
(1.2.4)
For a monodisperse sample, n has a single value for all molecules in the system,
whereas for a polydisperse sample, n would be characterized by distribution of
Introduction 7
Copyright © 2003 Marcel Dekker, Inc.
values.TheendchemicalgroupsXandYcouldbethesameordifferent,and
whattheyaredependsonthechemicalreactionsinitiatingthepolymerformation.
Uptothispoint,ithasbeenassumedthatalloftherepeatunitsthatmake
upthebodyofthepolymer(linear,branched,orcompletelycross-linkednetwork
molecules)areallthesame.However,iftwoormoredifferentrepeatunitsmake

upthischainlikestructure,itisknownasacopolymer.Ifthevariousrepeatunits
occurrandomlyalongthechainlikestructure,thepolymeriscalledarandom
copolymer.Whenrepeatunitsofeachkindappearinblocks,itiscalledablock
copolymer.Forexample,iflinearchainsaresynthesizedfromrepeatunitsAand
B,apolymerinwhichAandBarearrangedas
iscalledanABblockcopolymer,andoneofthetype
iscalledanABAblockcopolymer.Thistypeofnotationisusedregardlessofthe
molecular-weightdistributionoftheAandBblocks[7].
Thesynthesisofblockcopolymerscanbeeasilycarriedoutiffunctional
groupssuchasacidchloride(
COCl),amines( NH
2
),oralcohols( OH)are
presentatchainends.Thisway,apolymerofonekind(say,polystyreneor
polybutadiene)withdicarboxylicacidchloride(ClCO
COCl)terminalgroups
canreactwithahydroxy-terminatedpolymer(OH
OH)oftheotherkind(say,
polybutadieneorpolystyrene),resultinginanABtypeblockcopolymer,as
follows:
ClCCCl + OHOH
OO
CC
OO
OO
n
H
Cl
(1.2.7)
InChapter2,wewilldiscussinmoredetailthedifferenttechniquesofproducing

functionalgroups.Anothercommonwayofpreparingblockcopolymersisto
utilizeorganolithiuminitiators.Asanexample,sec-butylchloridewithlithium
givesrisetothebutyllithiumcomplex,
CH
3
CH
CH
3
CH
2
Cl + LiCH
3
CH
CH
3
CH
2
Li
+
.
.
.
Cl
–
(1.2.8)
8Chapter1
Copyright © 2003 Marcel Dekker, Inc.