A short fragment of a copolymer chain (three repeat units, end groups shown) is drawn. It is a synthetic rubber made by free radical copolymerisation, the diene being added 1,4. Which pair of monomers, shown as two molecules among the structures, gives it?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: D

A phenyl group on one carbon of the backbone indicates styrene, and the repeat units containing -CH2-CH=CH-CH2- come from buta-1,3-diene added 1,4, so the copolymer is Buna-S (SBR). Isoprene would leave a methyl branch on each C=C, alpha-methylstyrene would give a quaternary carbon, and chloroprene would give a Cl on the double bond.

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A short fragment of a copolymer chain (three repeat units, end groups shown) is drawn. It is a synthetic rubber made by free radical copolymerisation, the diene being added 1,4. Which pair of monomers, shown as two molecules among the structures, gives it?

Answer: D

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