Classification of Polymers Based on Molecular Forces

Based on the inter molecular forces polymers are classified into four types. They are Elastomers, Fibers, Thermo plastics and Thermo setting plastics

Classification of Polymers Based on Molecular Forces

(i) Elastomers: These are rubber like solid polymers in which the polymer chains are held together by weakest intermolecular forces

e.g., natural rubber, buna-S, buna-N etc.

The weak binding forces permit the polymers to be stretched. A few 'cross links' are introduced in between the chains, which help the polymer to retract to its original position after the force is released as in vulcanized rubber.

II) Fibres: Fibres belong to a class of polymers which are thread-like and can be woven into fabrics. These are widely used for making clothes, nets, ropes, gauzes, etc. Fibres possess high tensile strength because the chains possess strong intermolecular forces such as hydrogen bonding. The fibres are crystalline in nature and have sharp melting points.

 A few examples of this class are nylon-66, terylene and polyacrylonitrile.

(ii) Thermoplastics: These are linear polymers and have weak van der Waals' forces acting in the various chains. These forces are intermediate of the forces present in the elastomers and in the fibres. When heated, they melt and form a fluid which sets into a hard mass on cooling. Thus, they can be cast into different shapes by using suitable moulds.

 e.g., polyethene and polystyrene.

 (iv) Thermosetting plastics: These are normally semifluid substances with low molecular masses. When heated, they become hard and infusible due to the cross-inking between the polymer chains. As a result, they also become three-dimensional ln nature.

A few common thermosetting polymers are bakelite, melamine-formaldehyde resin and urea formaldehyde resin.