Which of the following polymers soften on heating and harden on cooling? What are the polymers with this property collectively called? What are the structural similarities between such polymers?

(N/A) Polythene,polyvinyls,and polystyrene soften on heating and harden on cooling.
Such polymers are collectively called $ \text{thermoplastic polymers} $.
These polymers consist of linear or slightly branched long-chain molecules.
They possess intermolecular forces whose strength lies between the strength of intermolecular forces of $ \text{elastomers} $ and $ \text{fibres} $.