Question

Which of the following polymers shows a sharp melting point?
A.Butyl rubber
B.Polystyrene
C.Bakelite
D.Nylon 6,6

Answer 1

Hint: The polymer showing a sharp melting point is clear, hard and brittle. It is used for protective packaging such as jewels.

Complete answer:
Butyl rubber is the synthetic rubber. It is a polymer with isobutylene and isoprene as its monomeric unit. It is produced by polymerisation of ninety eight percent isobutylene and two percent isoprene. This polymer has an excellent impermeability to gas diffusion and the long polyisobutylene segments of its polymer chains give it good flex properties. ( polyisobutylene is the homopolymer of isobutylene)
Polystyrene is also known as styron. It is an Addition polymer (formed by repeated addition of monomer molecules without elimination of anything). It is a polymer with styrene as its monomeric unit. Polystyrene are linear or slightly branched long chain molecules capable of repeatedly sifting on heating and hardening on cooling. This polymer has a very sharp melting point.
Bakelite is used in formation of electrical switches. It is a copolymer (addition polymer formed by polymerisation of two different monomers). Its monomeric unit is phenol + formaldehyde. Bakelite is a thermosetting polymer means these polymers are cross linked or heavily branched molecules and cannot be reused.
Nylon 6,6 also known as polyamide. It is a copolymer (addition polymer formed by the polymerisation of two different monomers). Its monomeric unit is hexamethylenediamine and adipic acid. It is a fibre polymer that means fibres are the thread forming solids which possess high tensile strength and strong intermolecular forces.

Thus, the correct option is option (B).

Note:
Vulcanisation of rubber is the process to improve physical properties of natural rubber at high temperature. As natural rubber becomes soft at high temperatures. This process consists of heating a mixture of raw natural rubber with sulphur in order to form sulphur cross links at the reactive sites of double bond. Vulcanised rubber also has a sharp melting point.