question_answer 83)

  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 ? Bakelite, urea-formaldehyde resin, polythene, polyvinyl, polystyrene.  

Answer:

                  Polythene, polyvinyl (PVC, teflon, acrilan, etc.), polystyrene soften on heating and, harden on cooling. Such polymers are called thermoplastic polymers. These polymers are linear or slightly brnached long chain molecules. Their intermolecular forces of attraction lie in between those of elastomers and fibres. For further details, refer to sec. 15.5.4, page 15/7.