FJ/Chemistry Unit, KMPk/Mac 2006 1

CHAPTER 21

POLYMERS

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21.1 : Introduction

Polymer- is a macro molecule that is made up of many small

repeating units called monomers linked together by covalent bond.

- polymer can be represented by their repeating unit in the long chain.

Monomer - is a basic molecular units that can joined to many others

to form a polymer.

nA - A-n

polymer

monomer

polymer (repeating

unit)

nnA - A- A- A- A- A- A- A- A-

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Homopolymer

- a polymer formed from only one types monomer units.

- Example :

nA - A-n

ethene (ethylen

e)

polyethene

(polyethylene)

nCH2 CH2 - CH2CH2-n

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Copolymer

- a polymer formed from two or more different monomers.

- Example :

1,1-dichloroethene

1-chloroethene

Saran®

nnA + nB - A- B-

nCH2 CCl2 + nCH2 CHCl - CH2- CCl2- CH2- CHCl-n

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21.2 : Structures of Polymers

21.2.1 : Linear Polymers

Linear polymer is a polymer consist of monomers that are linked in straight and long continuous chain.

Linear or straight-chain polymer can be folded back upon themselves in a random fashion.

Linear polymer is recycleable because it is soft and can be reformed when heated.

n- A- A- A- A- A- A- A- A-

monomers link together in a straight chain folded linear

polymer in a random fashion

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21.2.2 : Cross-linked Polymers

Cross-linked polymer contains branches that connect linear polymer chain, as shown in the figures below.

Cross-linked polymer is harder (rigid) and more elastic polymer compared to linear polymer.

It also cannot be remelted or remolded again.

The equation below shows the chemical reaction for the rubber vulcanization process.

• Long polymer chain cross-linked by branched

- A- A- A- A- A- A- A- A- A- A- A- A-

- A- A- A- A- A- A- A- A- A- A- A- A-

X X

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In a vulcanization process, long chain of polyisoprene are cross-linked by sulphur atoms.

After vulcanization rubber becomes more stable over wide ranges of temperature and far more durable than natural rubber.

- CH2C CH- CH2- +

CH3 CH3

- CH2C CH- CH2-

sulphur

CH3

- CHC CH- CH2- CHC CH- CH2-

S

- CHC CH- CH2- CHC CH- CH2-

CH3

CH3 CH3

S

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21.3 : Types of Polymers

21.3.1 : Natural Polymers

Natural polymers are polymers that synthesized in nature or naturally occurring polymers.

i. Proteins

Protein are the most abundant organic molecules in animals such as enzymes, hormones, hemoglobin and many other things.

It is a natural polymer built from amino acids linked by amide bonds.

HN- C- C

OH

R n

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ii. Carbohydrates

Carbohydrates such as starch is also a polymer.

i. Starch (amylose)

ii. Starch (amylopectin)

- contains α-(1,4)-glycosidic and α-(1,6)-glycosidic linkages.

O O

O

H HOO OH

H H

H

HH

CH2OH CH2OH

OH

OH

OH

H

H

H

nα-(1,4)-glycosidic linkages

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iii. Natural Rubber

Natural rubber is a polymer of 2-methyl-1,3-butadiena, also known as isoprene.

Another name for natural rubber is cis-1,4-polyisoprene.

All the double bond in natural rubber are cis- configuration.

Natural rubber is soft, not strong or elastic and sticky, that makes it less useful.

In order to make it more useful rubber has to undergo a vulcanization process.

n CH2=C- CH=CH2 - CH2- C=CHCH2-

CH3 CH3 n

isoprene cis-polyisoprene

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21.3.2 : Synthetic Polymers

Synthetic polymers are polymers that are prepared in industries from monomers that have gone through polymerization process.

Polymerization is a process that combines monomers to form polymers.

Synthetic polymers can be classified base on their method of preparation ( polymerization process ).

21.3.2.1 : Addition Polymerization

Addition polymerization is the addition reaction in which unsaturated monomers are joined together by covalent bonds to form a polymer without elimination of a small molecule.

Polymers obtained by addition polymerization are called addition polymers.

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Therefore, addition polymer always involves the polymerization of monomers which have double bond within the monomers.

Peroxide is used as initiator in addition polymerization.

i. Formation of polyethene

ii. Formation of polyvinyl chloride

n CH2 CH2 - CH2- CH2-ROOR ( )n

n HC CH2 - HC- CH2-ROOR ( )n

Cl Cl

ethene polyethene

chloroethene

polychloroethene (polyvinyl chloride or

PVC)

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iii. Formation of polystyrene

iv. Formation of polyisopropene

phenylethene

(styrene)

Polyphenylethene

(polystyrene)

isoprene polyisoprene

n HC CH2 - HC- CH2-ROOR ( )n

n CH2=C- CH=CH2 - CH2- C=CHCH2-

CH3 CH3 n

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21.3.2.2 : Condensation Polymerization

Condensation polymerization is a process that combines the monomers with elimination of a small molecule such as water, methanol, hydrogen chloride or ammonia to form a polymer.

The polymers obtained from condensation polymerization are called condensation polymers.

The monomers involves in this polymerization must have at least two identical or different functional group in the molecule.

When a carboxylic acid with two –COOH group reacts with an amine with two –NH2 groups, a polyamide is formed.

When a carboxylic acid with two –COOH group reacts with an alcohol with two –OH groups, a polyester is formed.

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(A). Polyamides

i. Formation of Nylon 6,6

ii. Formation of Nylon 6

hexane-1,6-diamine

Nylon 6,6

OO

n H2N- (CH2)6- NH2 + n HO- C- (CH2)4- C- OH

- N- (CH2)6- N- C- (CH2)4- C- + n H2O

O OH H

( )n

hexane-1,6-dioic acid

( )nn H2N- (CH2)5- C- OH

O O

- NH- (CH2)5- C- + n H2O

Nylon 66-aminohexanoic acid

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iii. Formation of Kevlar

(B). Polyester

The repeating functional groups in this polymer chain are ester.

The most familiar polyester is polyethylene terephthalate known as Dacron and Terylene.

1,4-diaminobenzene

Kevlar

terephthalic acid

n H- N- - N- H + n Cl- C- - C- Cl

O OHH

N- - N- C- - C

H H OO

n + n HCl

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The polymer is formed by the reaction of ethylene glycol with methyl ester or terephtalic acid.

In this process, a molecule of methanol is split out for each new ester group formed.

i. Formation of Dacron

Dacron or poly(ethylene terephthalate)

metanol

O O

n CH3O- C- - C- OCH3 + n HO- CH2CH2- OH

- O- CH2CH2- O- C- - C- + n CH3OH

O O

( )n

1,2-ethanediol (ethylene glycol)

dimethyl terephthalate

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ii. Formation of Terylene

Terylene

ethane-1,2-diol

benzene-1,4-dicarboxylic acid

water

OO

n HO-CH2CH2-OH + n HO-C- -C-OH

-O-CH2CH2-O-C- -C- + n H2O

O O

( )n

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21.4 : Uses of Synthetic Polymers

No.

Polymer Uses

1 Polyethene plastics, drinking bottles, toys

2Polyvinyl

chloridepiping, floor tiles, clothing, toys,

wire covering

3 Polystyrenecontainers, thermal insulation-ice

buckets

4 Nylon 6 Textile

5 Nylon 6,6 Sweater

6 Kevlar Bullet proof vest

7 Dacron Fabric

8 Terylene Fiber-optic material