Question

Which one of the following statements is/are true?

• A. In vulcanization the formation of sulphur bridges between different chains make rubber harder and stronger.
• B. Natural rubber has the trans-configuration at every double bond.
• C. Natural rubber is a cis-1,4-polyisoprene.
• D. Buna-N is a copolymer of butadiene and acrylonitrile.

Answer 1

Answer: (A), (C), (D)

Buna-N is a copolymer of butadiene and acrylonitrile.

Isomer cis-1,4-polyisoprene is a major ingredient of nature rubber whereas trans-1,4-polyisoprene is a major ingredient of gutta-percha. Natural rubber has all cis-configuration.
All statements expect (b) are correct.Vulcanization makes rubber more strong, tough and elastic. Natural rubber is mixed with 3-5% sulphur and heated at 373 K to 415 K, which results in cross linking of chains of cis-1,4-polyisoprene through disulphide $(-S-S-)$ bonds. On vulcanisation, sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened.

The probable structures of vulcanised rubber molecules are depicted below:Buna-N is a copolymer of 1,3-butadiene and acryonitrile.