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59.2 CLASSIFICATION OF POLYMERS

Polymers are classified in a number of ways depending upon one criterion or the other as described below.

On the basis of source or origin, the polymers are classified into two types:

Natural polymers and Synthetic polymers.

1.      Natural Polymers. Polymers found in nature, mostly in plants and animal sources, are called natural polymers. A few examples are:

a. Polysaccharides. Starch and cellulose are very common examples of polysaccharides. They are the polymers of glucose. Starch is a chief food reserve of plants while cellulose is chief structural material of plants.

b. Proteins. These are the polymers of α-amino acids. They are building blocks of animal cells. They constitute indispensable part of our food. Wool, natural silk, leather, etc., are proteins.

c. Nucleic Acids. These are the polymers of various nucleotides. RNA and DNA are common examples.

d. Natural Rubber. Substance obtained from latex is a polymer of 2-methyl buta-I, 3-diene (isoprene).

It may be noted that polymers like polysaccharides, nucleic acids, proteins, etc., which control various life processes in plants and animals are also called biopolymers.

2.      Semi-Synthetic Polymers. These are mostly derived from naturally occurring polymers by carrying out chemical modifications. For example,

H2SO4

Cellulose + (CH3CO)2O                →                   Cellulose diacetate

Acetic anhydride

Cellulose diacetate is used in making threads, films, glasses, etc.

3.      Synthetic Polymers. The polymers which are prepared in the laboratory are referred to as synthetic polymers or man-made polymers. Some examples of the synthetic polymers are polyethylene, polystyrene, PTFE synthetic rubber, nylon, PVC, bakelite, teflon, orion, etc.

The synthetic polymers can be further classified as these made up of monomers and comonomer units.

The polymers are also classified based on:

a)      Structure

b)      molecular forces

c)      modes of polymerisation.