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Polymers and Composite Materials

Shibu G. Pillai

Chemical Engineering Department

shibu.pillai@nirmauni.ac.in

Contents

• Classification of Polymers

• Types of polymerization

• Elastomers/ Rubber

• Advanced Polymeric Material

• Biopolymers

• Composite Materials

POLYMERS (the whole train) are made out of MONOMERS

(individual cars of the train) joined together.

• Polymer: High molecular weight moleculemade up of a small repeat unit (monomer).

– A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-

• Monomer: Low molecular weight compoundthat can be connected together to give apolymer

• Oligomer: Short polymer chain (unit 6-12)

Polymers: Introduction

Classification of Polymers

I. On the basis of SOURCE or ORIGIN(Conventional Classification)

(a) Natural/Biopolymers (found in nature)examples: cellulose, rubber, RNA, DNA, protein

(b) Semi-synthetic polymers (main source is naturebut with some modification as per our need)examples: cellulose-nitrate,-acetate, vulcanizedrubber etc.

(c) Synthetic Polymers (which are prepared in thelab/industries) examples: polyethene, PVC,nylon, polyester etc.

II. Depending upon the mode of synthesis

a) Addition Polymer

b) Condensation polymer

• ADDITION POLYMER

When the monomer units are repeatedly addedto form long chains without the elimination ofany by-product molecules, the product formedis called addition polymers

Examples: polyethene, PVC, Teflon,polyurethane, SBR etc.

• CONDENSATION POLYMER

When the monomer units are react together,with the elimination of by-product moleculessuch as water, carbon dioxide, HCl, ammoniaalcohol etc., the product formed is calledcondensation polymers

Examples: nylon-6, nylon-6,6, epoxy resins, UFresins, Kevlar (polyamide) etc.

III. Depending upon the nature of the repeatingstructural units

a) Homo-polymer

b) Co-polymer

• HOMO-POLYMER

The polymer formed from one kind ofmonomers, called homo-polymer.

Examples: Polyethene, PVC, Teflon, etc.

Types of Homo-polymer

a) Linear b) Branched c) Cross-linked

Linear polymers

• These polymers consist of long and straight chains.

• Examples are high density polythene, PVC, etc.

Branched Polymers

• These polymers contain linear chains having some branches, e.g.,

• Examples are low density polythene, amylopectine etc.

Cross-linked Polymers

• Monomeric units are linked together to constitute a 3-dimensional network structure

• Hard and rigid

• Example: vulcanized rubber etc.

• CO-POLYMER

The polymer formed from more than one kindof monomers, called co-polymer.

Examples: Terylene, Nylon-6,6, SBR, Saran,Kevlar etc.

Types of Co-polymer

IV. Based on molecular forces/applications• polymer applications in different fields depend

on their unique mechanical properties liketensile strength, elasticity, toughness, etc.

• These mechanical properties are governed byintermolecular forces, e.g., van der Waalsforces and hydrogen bonds, present in thepolymer.

• the polymers are classified on the basis ofmagnitude of intermolecular forces present inthem.

a) Elastomers (b) Fibers (c) Plastic

Elastomers

• These are rubber – like solids with elasticproperties.

• the polymer chains are held together by the weakest intermolecular forces.

• These weak binding forces permit the polymer to be stretched.

• A few ‘crosslinks’ are introduced in between the chains, which help the polymer to retract to its original position after the force is released as in vulcanised rubber.

• The examples are buna-S, buna-N, neoprene

Fibers

• Fibres are the thread forming solids whichpossess high tensile

• These characteristics can be attributed to thestrong intermolecular forces like hydrogenbonding.

• These strong forces also lead to close packing ofchains and thus impart crystalline nature.

• Examples are polyamides (nylon 6, 6),polyesters (terylene)

Thermoplastic Polymers

• These are the linear or slightly branched longchain molecules capable of repeatedly softeningon heating and hardening on cooling.

• These polymers possess intermolecular forcesof attraction intermediate between elastomersand fibres.

• Some common thermoplastics are polythene,polystyrene, polyvinyls, etc

Thermosetting Polymers

• These polymers are cross linked or heavilybranched molecules, which on heating undergoextensive cross linking.

• chain motion is greatly restricted by a highdegree of crosslinking.

• These cannot be reused.

• Some common

• examples are bakelite, urea-formaldelyderesins, epoxy resins etc.

Types of Polymerization

I. Addition Polymerization

II. Condensation Polymerization

Addition polymerization• the molecules of the same monomer or

different monomers add together on a largescale to form a polymer.

• The monomers used are unsaturatedcompounds, e.g., alkenes, alkadienes and theirderivatives.

• This mode of polymerisation leading to anincrease in chain length or chain growth cantake place through the formation of either freeradicals or ionic species.

• However, the free radical governed addition orchain growth polymerisation is the mostcommon mode.

Examples of Addition polymerization

Condensation polymerization• Polymerization generally involves a repetitive

condensation reaction between two bi-functionalmonomers.

• These poly-condensation reactions may result in theloss of some simple molecules as water, alcohol, etc.,and lead to the formation of high molecular masspolymers.

• In these reactions, the product of each step is again abi-functional species and the sequence ofcondensation goes on.

• Since, each step produces a distinct functionalisedspecies and is independent of each other,

• this process is also called as step growthpolymerisation

Examples of condensation polymerization

Examples of condensation polymerization

Rubber

TacticityTacticity – stereoregularity or spatial arrangement of R units

along chain

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

isotactic – all R groups on same side

of chain

C C

H

H

H

R

C C

H

H

H

R

C C

H

H

H

R R

H

H

H

CC

syndiotactic – R groups alternate

sides

Tacticity (cont.)atactic – R groups randomly

positioned

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

Biopolymer

I. Starch

II. Cellulose

GlucoseStructural formula.

Straight chain glucose

H-C=O

|

H-C-OH

|

HO-C-H

|

H-C-OH

|

H-C-OH

|

CH2OH

Glucoseglucose bending

GlucoseTwo ring-shape

versions

alpha-glucose

beta-glucose

Glucose bends itself into 4 different shapes millions of times

a second

1

4

6

2

3

5

Used in making

cellulose

Used in making starch

flips either waybends

(a) and glucose ring structures

Glucose Glucose

4 1 4 1

(b) Starch: 1–4 linkage of glucose monomers

(c) Cellulose: 1–4 linkage of glucose monomers

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