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Polymers

Poly means many

Mer means unit

Polymers are macromolecules formed by the combination of many small moleculescalled monomers.

The molecular weight of polymer ranges from 500 to 106.

The process of formation of polymer from monomers is called polymerisation.

Degree of polymerization (DP)is the number of repeating units (monomers) present inthe polymer

DP = mol.wt of polymermol.wt of monomer

Example:

Polyethylene is made by repeatedly linking ethylene (monomer)

n CH2= CH2 ( CH2 CH2 ) n

Ethylene polythene(monomer)

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Functionality

The number of reactive or bonding sites present in the monomer is called its

functionality.

Monomers which possess more than one reactive site alone can undergopolymerization.

Functionality Examples

0 CH4, CCl4, C6H6

1 ROH , RCl , RCOOR, RNH2

2 Amino Acids , CH2= CH2 (ethene),CH2OH CH2OH (glycol)

3 CH2OH CHOH CH2OH (glycerol)C6H5OH (phenol)

4 CH CH (acetylene)

All monomers are molecules but all molecules are not monomers

For example Water is a molecule but does not undergo polymerization (functionality is0).

On the other hand ethylene molecule polymerises to give polyethylene hence it is amonomer (functionality 2).

In other words for a molecule to become monomer it should have at least two bondingsites ie. Its functionality should be at least 2.

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Classification

1. Based on Origin

Natural, Synthetic and Semi synthetic

Natural/ Bio polymers : Cellulose, Starch, Proteins, Rubber etc.,

Semi synthetic:Celluloid , Ethyl Cellulose, Cellulose Acetate, Carboxy methylcellulose (CMC)

Synthetic (organic) : Polyamides, Poly esters, Poly ethers, PVC, PS PE etc.,

Silicone is an inorganic synthetic polymer

Semi syntheticCellulose acetateVulcanised rubber

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Uses of Synthetic Polymers

No. Polymer Uses1 Polyethene plastics, drinking bottles, toys

2Polyvinylchloride

piping, floor tiles, clothing, toys,wire covering

3 Polystyrenecontainers, thermal insulation-icebuckets

4 Nylon 6 Textile

5 Nylon 6,6 Sweater

6 Kevlar Bullet proof vest

7 Dacron Fabric

8 Terylene Fiber-optic material

2. Based on Degree of polymerization

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3. Based on the Type of Monomer

Homo polymer Prepared by the self polymerization of same type of monomers (A)

- CH2 ( CH2 CH2) CH2 CH2- (polyethene)

Types: based on the arrangement of monomers

Linear homopolymer: (HDPE)

Branched homo polymer: (LDPE)

A A A A

A

A

A A A A

A

A

A A A A

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Cross linked polymer (Poly Acetylene)

A A A A

A A A A

A

A

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Heteropolymer / Copolymer:

Prepared by cross polymerization of two or more types of monomersExample: Nylon 6,6 , Urea formaldehyde , Buna S- rubber ,Buna Nrubber etc.,

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Block copolymer

Graft CopolymerIt is a special kind of branched copolymer where the main chain and side chains are made upof different types of monomers

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For example the cationic exchanger of the demineraliser is prepared bygrafting styrene into poly ethylene base polymer and then sulphonating

the resulting graft co polymer.

Scheme of preparing cationic exchanger:

4.Based on main chain (back bone/ skeleton)

i) Homo chain: made up of single type of atom (ex) PE , Buna S-rubber

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ii) Hetero chain: made up of different types of atoms (ex) nylons,

polyesters, PVA, PVAc etc.,

5. Based on molecular forces (thermal behaviour)

Thermoplastics / Thermoforming Plastics: Ex. PE, PP, PVC, PS

Thermosetting plastics: Ex. Bakelite, Polyester, Urea- formaldehyde, Epoxy resins

Thermoplastics (TP) Thermosettes (TS)

They are formed by additionpolymerization

They are formed by condensationpolymerization

They are linear / branched long chainpolymers

They consist of three dimensional networkstructure joined by strong covalent bonds

On cooling they get hardened On heating they get hardened

They are soluble in organic solvents Insoluble in organic solvents

Softens on heating , because VanderWaals forces existing between theindividual chains can break easily by heatand pressure

They do not soften on heating because thecovalent bonds retain their strength onheating

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They can be remoulded any number oftimes

Once set, they cannot be remoulded

They are soft, weak and less brittle They are hard, strong and more brittle

5. Based On Application

(a)Resins: Half polymerized polymers are called resinsThey are used as ion exchangers and in the preparation of adhesives

(b) Fibres: Usually polymers with high tensile strength will be drawn into wires.Examples: PET, nylons etc.,

(c) Elastomers(Ex) rubbers

(d) Plastics; TP and TS

6. Method of synthesis

Addition polymer: Polymers prepared by addition reaction

Ex.: PE,PVC,PVA , PS, Buna S-rubber etc.,

Condensation polymer: Polymers prepared by condensation reaction.

Ex.: Poly amides, Poly Esters, Poly Ethers, PET, Bakelite, PC, Poly Urethane etc.

Addition Polymerization / Polymers Condensation polymerization /Polymers

Monomers add on to give polymerswithout forming by products

Monomers condense to givepolymers and by products like H2O, HCl,MeOH etc. are formed.

Monomers must have atleast one doublebond

Monomers must have atleast two identicalor different functional groups

It is a chain forming reaction It is a step wise reaction

The polymer product is formed at once The polymer product is formed stepwisesteadily

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Molecular weight of the polymer is anintegral multiple of the molecular weight ofthe monomers

Molecular weight of the polymer is lessthan the integral multiple of the monomers

Mostly Thermoplastics are obtained Mostly Thermoset resins are obtained

7. Based on Tacticity

Tacticity is the orderly arrangement of groups around polymer main chain

Ex: Poly Styrene

If all of the phenyl groups are on the same side of the chain, the polymer is

isotactic.

If the phenyl groups come on alternating sides of the chain, the polymer is

syndiotactic.If the phenyl groups are on both sides and right and left following no particular

order, in a random fashion, then the polymer is atactic.

Thermosetting Thermoplastic

Rigid Epoxy PS

Urea-formaldehyde PVC

Hard rubber PP

Flexible

Highly loaded or highly

vulcanized rubbers

PE, Acetate copolymers,

PVC

Rubbery Vulcanized rubbers TPE

Un lasticised

Plasticised

Thermoplastic elastomer

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I

Extra information

Biopolymers (Natural Polymers)

All organic polymers are threads made using repeating units, the monomers, that areeither similar or different.

(i) .The similarly beaded "homo polymers" are made by linking together many ofthe same monomers.

Starch or cellulose are homo polymers

ii). The differently beaded "hetero polymers" are made of different monomers."Hetero" is a prefix that implies that components are different.

DNA, RNA are both heteropolymers.

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Inorganic Synthetic Polymers

Hetero polymer

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Plastics Application Summary

Material Types Industry Types

Acrylic Medical equipment

Polycarbonate CD, Bullet Proof Helmet

PVC Defence, Medical

Polypropylene Aerospace, syringe

SBR Elastomer

PEEK(Poly Ether Ether Ketone)

Engineering

PVDC(Poly VinyliDene Chloride)

Food Processing

PTFE(Teflon)

Design houses

Kevlar Strong Fibre