Which of the following polymer is NOT a thermoplastic ?

Question

UnlockIAS · Accepted Answer

Correct — B, Neoprene. Neoprene (polychloroprene) is a synthetic rubber — an elastomer — not a thermoplastic. Like other rubbers it is cross-linked (vulcanised) into a permanent network, so it does not soften and remould on repeated heating the way a thermoplastic does; it is elastic and heat-set. The other three — Teflon (PTFE), polystyrene and polythene (polyethylene) — are classic thermoplastics that soften on heating and harden on cooling, and can be melted and reshaped again. So among the four, Neoprene is the one that is NOT a thermoplastic.

Why the other options are wrong — (a) Teflon (polytetrafluoroethylene, PTFE) is a thermoplastic — a long-chain fluoropolymer that softens/flows on heating; it is used for non-stick coatings precisely because it is a stable thermoplastic, so it is not the exception asked for.  (c) Polystyrene is a well-known thermoplastic (disposable cups, packaging, thermocol/expanded polystyrene); it melts and can be re-moulded, so it does not fit 'NOT a thermoplastic'.  (d) Polythene (polyethylene) is the archetypal thermoplastic used for bags and films; it softens on heating and re-solidifies on cooling, so it is not the odd one out.

Concept: Polymers are grouped by their response to heat. Thermoplastics (linear/branched chains held by weak forces) soften on heating and can be remelted and reshaped repeatedly — e.g., polythene, polystyrene, PVC, Teflon. Thermosetting plastics set into a rigid cross-linked network that cannot be remelted (e.g., bakelite). Elastomers (rubbers) are lightly cross-linked polymers that stretch elastically — e.g., natural rubber and neoprene.

State PCS 2020 Q93 — Science & Technology PYQ with Answer

State PCS 2020 Q93 — Science & Technology PYQ with Answer