NCERT Book Class 12 Chemistry Polymers

Do you think that daily life would have been easier and colourful without the discovery and varied applications of polymers? The use of polymers in the manufacture of plastic buckets, cups and saucers, children’s toys,
packaging bags, synthetic clothing materials, automobile tyres, gears and seals, electrical insulating materials and machine parts has completely revolutionised the daily life as well as the industrial scenario. Indeed, the
polymers are the backbone of four major industries viz. plastics, elastomers, fibres and paints and varnishes. The word ‘polymer’ is coined from two Greek words: poly means many and mer means unit or part. The
term polymer is defined as very large molecules having high molecular mass (103-107u). These are also referred to as macromolecules, which are formed by joining of repeating structural units on a large scale. The repeating structural units are derived from some simple and reactive molecules known as monomers and are linked to each other by covalent bonds. This process of formation of polymers from respective monomers is
called polymerisation. The transformation of ethene to polythene and interaction of hexamethylene diamine and adipic acid leading to the formation of Nylon 6, 6 are examples of two different types of polymerisation
reactions.

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Classification Based on Source

Under this type of classification, there are three sub categories.
1. Natural polymers
These polymers are found in plants and animals. Examples are proteins, cellulose, starch, resins and rubber.
2. Semi-synthetic polymers
Cellulose derivatives as cellulose acetate (rayon) and cellulose nitrate, etc. are the usual examples of this sub category.
3. Synthetic polymers
A variety of synthetic polymers as plastic (polythene), synthetic fibres (nylon 6,6) and synthetic rubbers (Buna - S) are examples of manmade polymers extensively used in daily life as well as in industry.

Classification Based on Structure of Polymers

There are three different types based on the structure of the polymers.
1. Linear polymers
These polymers consist of long and straight chains. The examples are high density polythene, polyvinyl chloride, etc.

2. Branched chain polymers
These polymers contain linear chains having some branches, e.g., low density polythene.

3. Cross linked or Network polymers
These are usually formed from bi-functional and tri-functional monomers and contain strong covalent bonds between various linear polymer chains, e.g. bakelite, melamine, etc.

Excercise

15.1 Explain the terms polymer and monomer.
15.2 What are natural and synthetic polymers? Give two examples of each type.
15.3 Distinguish between the terms homopolymer and copolymer and give an example of each.
15.4 How do you explain the functionality of a monomer?
15.5 Define the term polymerisation.
15.6 Is ( NH-CHR-CO )n, a homopolymer or copolymer?
15.7 In which classes, the polymers are classified on the basis of molecular forces?
15.8 How can you differentiate between addition and condensation polymerisation?
15.9 Explain the term copolymerisation and give two examples.
15.10 Write the free radical mechanism for the polymerisation of ethene.
15.11 Define thermoplastics and thermosetting polymers with two examples of each.
15.12 Write the monomers used for getting the following polymers.
(i) Polyvinyl chloride (ii) Teflon (iii) Bakelite
15.13 Write the name and structure of one of the common initiators used in free radical addition polymerisation.
15.14 How does the presence of double bonds in rubber molecules influence their structure and reactivity?
15.15 Discuss the main purpose of vulcanisation of rubber.

Please refer to attached file for NCERT Class 12 Chemistry Polymers