Polymers

Polymers are repeating macromolecules , that form long chains of carbon .

## Classification

**Natural Polymers**

**Synthetic Polymers**

**Semi Synthetic Polymers**

**Linear Polymers**

**Branched Polymer**

**Cross-linked Polymers**

**Addition Polymers**

It composes of same or different monomers linked in a long chain . e.g. Polythene , Orlon , Teflon /

**Condensation**

**Elastomers**

**Fibers**

**Thermoplastic Polymers**

**Thermo-setting Polymers**

## Addition Polymerisation

**Free Radical Polymerisation**

1) Formation of free radicals . This takes place due to breaking of a bond .

2) The free radical molecule reacts with n number of ethylene molecules to form long chains .

3) The chain can be stopped by stopping the supply of ethylene . This step is called as chain terminating step .

An initiator is used which undergoes decomposition easily to form free radicals , which initiate the reaction .

e.g. benzoyl peroxide , tert - butyl peroxide , acetyl peroxide .

## Homopolymers and Heteropolymers

Homopolymers - Same Monomers

e.g. Polythene , Orlon , Teflon , Polyvinyl chloride , Polystyrene .

Heteropolymers - Different Monomers

e.g. Nylon-6,6 ; Nylon - 2,6 ; terylene , Buna S , Buna N .

## Polythene

**LDPE**

Ethene is heated at 200o C to 300o C at a pressure 1000 atm . A small amount of oxygen is used as a catalyst . The initiator peroxide is formed during the process due to oxygen .

**HDPE**

Ethene is heted 100o C at 6-7 atm . Ziegler - Natta catalyst is used during the process . Ziegler - Natta catalyst i TiCl4 + (C2H5)3Al

HDPE is also called as coordination polymer since titanium complex is formed .

## Orlon (Polyacrylonitrile)

-[--H2C-(CN)CH2--]-n

prepared from monomer acrylonitrile .

used in artificial wool and synthetic carpets .

## Teflon (Polytetrafluoroethylene)

-[--F2C-CF2--]-n

Obtained from monomer tertafluoroethylene .

Used in oil seals of gaskets and valves , used in non-stick coating on cooking utensils .

## Nylon

**Nylon - 6**

-[--(O=)CH2-(CH2)5-N(H)--]-n

Obtained by heating ε-Caprolactum at a high temperature (533 K) in an inert atmosphere .

Nylon-6 is also known as Perlon .

**Nylon -6,6**

-[--(H)N-(CH2)6-N(H)-(O=)CH2-(CH2)4-(C=o)--]-n

Prepared from hexamethylenediamine and adipic acid .

**Nylons** are used in in making bristles for brushes , fishing nets , bed covers , toys and in textile industry .

blended with wool to make socks and sweaters .

used in manufacture of colours and climbing ropes .

## Terylene or Dacron

-[--H2C - CH2 - O - C(=O)-Ar-C(=O) - O --]-n

(The Benzene is attached to at the para positions )

Polymers having ester linkages are called as polyesters . Terylene is a polyester .

Terylene or Dacron is prepared from Ethylene glycol and Dimethylterephthalte (DMT) by heating at 420-460 K .

Terylene is resistant to heat , light ,chemicals ,crease , moths and bacteria .

It is used in manufacture of wash and wear fabrics

It is blended with cotton to form terrycot and with wool to form terrywool . This increases their resistance to wear and tear .

It is used in preparation of fishing nets , ropes , trousers , magnetic tape recorders , tyres ,etc.

## Bakelite

-[--H2C-(OH)Ar(CH2) -(OH)Ar(CH2)---]-n

It is prepared from monomers Phenol and Formaldehyde .

linear chain of Bakelite is called as Novolac .

Low degree polymerization gives soft Bakelite ; used in making glue for binding laminated wooden planks and in varnishes .

High degree polymerization gives hard Bakelite ; used in making of electrical switches , plugs , fountain pens , phonograph records , handles of cooker , frying pans , combs .

## Urea Formaldehyde Polymer

Prepared from monomers Urea (NH2-CO-NH2) and Formaldehyde .

Used as a moulded plastic .

## Melamine Formaldehyde Polymer

Prepared from monomers Melamine and Formaldehyde .

Used in manufacture of crockeries .

## Natural Rubber

It is a natural polymer . It is obtained from latex which is a colloidal solution of of rubber particles in water .

Polyisoprene is a linear polymer of isoprene . It contains double bond in each repeating unit .

Thus , Polyisoprene shows geometric isomerism . Natural Rubber is cis1,4-polyisoprene .

The cis- polyisoprene molecule is held together by weak Van der Waals Forces . Gutta-Percha is trans-1,4-polyisoprene . It has zigzag chains which fit in one another . It is crystalline and non elastic while cis isomer (Natural Rubber) is elastic .

## Vulcanized Rubber

Vulcanization is the process which consists of heating raw rubber with sulphur and an appropriate additive at a temperature ranging between 100o C to 150o C . Natural rubber when mixed with 3 to 5 % of Sulphur , and heated at 100o C to 150o C , forms cross linking of cis - 1,4 - polyisoprene chains through disulphide bonds . Cross linking prevents the polymer from being torn when it is stretched . By controlling the amount of sulphur used in vulcanization , the physical properties of rubber can be altered to suit requirements . When 20-305 sulphur is used , hard rubber is obtained . Rubber made with 3 to 10% sulphur is little hard .

**Buna-S (butadiene rubber)**

Prepared from monomers buta-1,3-diene and Styrene (Ar-H2C=CH2)

**Buna-N**

Prepared from monomers buta-1,3-diene and acrylonitrile

**Neoprene Rubber**

Prepared from monomer 2-Chlorobuta-1,3-diene

**Butyl Rubber**

Prepared from monomer isobutylene and isoprene

## Biodegradable & Non-Biodegradable Polymers

The polymers which are degraded by micro-organisms within a suitable period so that the polymers and thir degraded products do not cause any serious effects on the environment are called biodegradable polymers .

**PHBV (polyhydroxy butyrate-CO-β-hydroxyvalerate)**

It is prepared from monomers 3-hydroxy butanoic acid and 3-Hydroxy pentanoic acid .

**Dextron**

It is prepared from monomers glycollic acid and lactic acid .

**Nylon - 2 - Nylon - 6**

It is prepared from the monomers glycind and ε-amino caproic acid

## Other Polymers

### ABS Plastic

It is obtained by combination of butadiene(B) , Styrene(S) and acrylonitrile(A) . It is tough and strong .

### Saran

It is obtained from combination of vinylidene chloride and vinyl chloride . It is used as film for wrapping food .

### Nylon - 6,10

-[--(H)N-(CH2)6-N(H)-(O=)CH2-(CH2)8-(C=o)--]-n