JEE Main · 2021 · 25 Jul 2021 · Shift 1 · Polymers

is a repeating unit for

(A)Neoprene
(B)Novolac✓ Correct
(C)Buna-N
(D)Acrilan

Answer: (B)

Solution

The repeating unit is a phenol ring carrying a free hydroxyl group and joined to its neighbours through

- C H_{2} -

bridges at the two positions flanking that hydroxyl. Methylene bridges between phenol rings are what the acid catalysed condensation of phenol with methanal produces, each formaldehyde molecule supplying one bridging carbon and losing water; while the chain stays linear and uncrosslinked the resin is novolac. Neoprene is polymerised chloroprene, Buna-N a buta-1,3-diene and acrylonitrile copolymer and acrilan is polyacrylonitrile, and none of the three contains an aromatic ring at all. The unit shown is the repeating unit of novolac.

JEE Main · 2021 · 25 Jul 2021 · Shift 1 · Single correct option

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