CBSE Class 12th Chemistry Notes: Polymers (Part - II)

Gurmeet Kaur Created On: Nov 11, 2016 10:30 IST

The main topics covered in this part are:

•   Copolymerisation

•   Rubber

     o   Natural

     o   Synthetic

•   Biodegradable Polymers

•   Polymers of Commercial Importance

The key notes of the chapter are as follows:

Copolymerisation

It is a type of polymerisation reaction in which a mixture of more than one monomeric species is allowed to polymerise and form a polymer called copolymer.

Copolymer contains multiple units of each monomer.

For example: 1, 3-Butadiene and styrene can undergo copolymerization to form butadiene –styrene copolymer.

Rubber

Rubber is of two types: Natural and synthetic

1. Natural Rubber

It is a natural polymer possessesing elastic properties.

It is a linear 1, 4-polymer of isoprene (2-methyl-1, 3-butadiene).

Drawbacks of Natural Rubber:

•   It becomes soft at high temperature and brittle at low temperatures.

•   It is non-resistant to the attack of oxidizing agents.

Vulcanisation of Rubber: The process of adding sulphur to rubber to improve its physical properties is called vulcanisation of rubber.

Vulcanisatlon is carried out by adding sulphur (3-5%) and zinc oxide to the rubber, and then heating the object at about 110°Cfor about 20-30 minutes.

Zinc oxide accelerates the rate of vulcanisation

Sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened.

Thus about 5% sulphur is used for making tyre rubber and 30% of it for making battery case rubber.           

The improved properties of vulcanised rubber are:

(i) High elasticity.

(ii) Low water-absorption tendency

(iii) Resistance to oxidation.

2. Synthetic Rubber

Synthetic rubbers are polymers derived from 1, 3 - butadiene or 1, 3 - butadiene derivatives.

The synthetic rubber is of two types:

•   Neoprene
     o  It is a homopolymers of chloroprene (2-Chloro-1,3-butadiene).

     o  Uses: It is used for manufacturing conveyor belts, gaskets and hoses.

•   Buna-N

     o  It is a copolymer of 1,3-Butadiene with acrylonitrile (Buns-N) carried out in the presence of a peroxide catalyst.

      o  Uses: It is used in making conveyor belts and printing rollers.

Biodegradable Polymers

These are the synthetic polymers that are hydrolysed by enzymes and to some extent degrade by oxidation.

These polymers contain functional groups similar to the functional groups present in biopolymers.

Some important examples of biodegradable polymers are given below:

1.  Poly-hydroxybutyrate- co-β-hydroxy valerate (PHBV):

•   Preparation: It is a copolymer of 3-hydroxy butanoic acid and 3-hydroxy pentanoic acid in which the monomeric units are connected by ester linkages.

•   Uses: It is used in packaging, orthopaedic devices and even in controlled drug release.

2. Suture Polymer:

•  It is a copolymer of glycolic acid and lactic acid.

•  Sutures help the healing process by closing and sealing a wound.

•  Dextron was the first biodegradable suture made from biodegradable polyesters for post-operation sticher.

3. Nylon-2-Nylon-6:

It is a copolymer of (H₂N–CH₂–COOH) and amino caproic acid [H₂N (CH₂)₅ COOH]  and is biodegradable.

Polymers of Commercial Importance

Some Commercially Important Polymers, their monomers and uses are given below:

Polymer	Monomer	Uses
Polyvinyl chloride (PVC)	CH2=CHCl Vinyl Chloride	Manufacture of rain coats, hand bags, vinyl flooring, and water pipes.
Polyethylene	CH2=CH2 Ethylene	Manufacture of coats, wire insulators, bags
Polystyrene	CH2=CH‒C6H5 Vinylbenzene (Styrene)	As insulator, wrapping material, manufacture of toys, radio and television cabinets
Polyvinyl acetate (PVA)	CH2=CH‒OCOCH3 Vinylacetate	Making latex, paint
BUNA rubber	CH2=CH‒CH=CH2 1,3-Butadiene	Manufacture of tyres and hoses

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