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JEE Advanced levelSingle correct optionDifficulty 3 of 3pl243

The two monomers shown are copolymerised by free radical emulsion polymerisation. Which statement describes the product correctly?

  1. ACondensation copolymer; water eliminated; thermosetting
  2. BAddition homopolymer; used as a fibre
  3. CAddition copolymer; an elastomer in which each butadiene unit keeps one C=C
  4. DAddition copolymer in which no C=C remains in the chain; a rigid thermoplastic

Answer: C

Buta-1,3-diene and styrene both contain C=C, so they undergo chain-growth addition and the product, Buna-S (SBR), is an addition copolymer. The diene adds 1,4, so each butadiene-derived unit keeps one C=C, which can be vulcanised with sulfur, and the polymer is an elastomer. It is not formed by condensation, and the retained C=C bonds rule out a 'no C=C' product.
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