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 vulcanised rubber .
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 .
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 .
( Plasticizers are high boiling esters or haloalkanes . These are added to I plastics to make them soft rubber like . … J
Thermosetting plastics These are normally semifluid substances with low molecular masses . When heated , they become hard and infusible due to the cross-linking between the polymer chains . As a result , they also become three dimensional in nature . A few common thermosetting polymers are bakelite , melamine-formaldehyde resin and urea formaldehyde resin .