Define thermoplastic and thermosetting polymers. Give one example of each.
Thermoplastic Polymers: These are the linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling. These possess intermolecular forces of attraction intermediate between elastomers and fibres. For e.g. Polythene, Polyvinyl etc.
Thermosetting Polymers: These are cross-linked or heavily branched molecules which on heating undergo extensive cross-linking in moulds and again become invisible. These cannot be reused. For e.g. bakelite, urea-formaldehyde resins etc.