Question: 57: Which among the following is a thermoplastic polymer?
(1) Bakelite
(2) Polythene
(3) Urea-formaldehyde resin
(4) Melamine polymer
Answer: Option (2)
Explanation:
Thermoplastic polymers are polymers that soften on heating and can be remoulded repeatedly
without any change in their chemical structure.
Polythene is a thermoplastic polymer. It consists of long linear or slightly branched chains of repeating ethene units. The intermolecular forces between these chains are weak,
so when heated, the chains can slide over each other, making the polymer soft and mouldable.
Bakelite, urea-formaldehyde resin, and melamine polymer are thermosetting polymers.
These polymers have a highly cross-linked three-dimensional network structure.
On heating, they do not soften but instead become hard permanently due to the formation of strong covalent bonds between chains.
Therefore, among the given options, only polythene behaves as a thermoplastic polymer.