Polymers

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

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