Which of the following polymers soften on heating and harden on colling? What are the polyfmers with this property collectively called ? What are the structural similarites between such polymers? Bakelite urea formaldehyde resin , polythene, polyvinyls, polystyrene.

Explanation

The polymers which soften on heating and harden on cooling are known as thermoplastic polymers. The polymers belonging to this class are polythene, polyvinyls and polystyrene. These are all addition polymers and the attractive force are van der Waal's forces in nature. these are generally weak. That is why these polymers are of thermoplastic Bakelite, urea-formaldehyde resin are cross-linked in nature. These have been formed as result of condensation reactions and are therefore, hard and also rigigd. For details, consult section 5 and 6