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Which one of the following statements is not true ?
A
Buna-S is a copolymer of butadiene and styrene
B
Natural rubber is a 1, 4-polymer of isoprene
C
In vulcanization, the formation of sulphur bridges between different chains make rubber harder and stronger
D
Natural rubber has the trans-configuration at every double bond
Detailed Solution
Natural rubber is a linear 1,4-addition polymer of isoprene (2-methylbuta-1,3-diene).
It is cis-1,4-polyisoprene and has only the cis-configuration at every double bond.
Because of the cis arrangement the chains cannot pack closely; they are held by weak van der Waals forces and take up a coiled structure, which gives rubber its elasticity.
The all-trans polymer of isoprene is gutta-percha, which is hard and non-elastic.
So the statement that natural rubber has the trans-configuration at every double bond is not true.
The other statements are true: Buna-S is a copolymer of buta-1,3-diene and styrene; natural rubber is a 1,4-polymer of isoprene; and in vulcanization the sulphur cross-links (bridges) formed between different chains make the rubber harder and stronger.
It is cis-1,4-polyisoprene and has only the cis-configuration at every double bond.
Because of the cis arrangement the chains cannot pack closely; they are held by weak van der Waals forces and take up a coiled structure, which gives rubber its elasticity.
The all-trans polymer of isoprene is gutta-percha, which is hard and non-elastic.
So the statement that natural rubber has the trans-configuration at every double bond is not true.
The other statements are true: Buna-S is a copolymer of buta-1,3-diene and styrene; natural rubber is a 1,4-polymer of isoprene; and in vulcanization the sulphur cross-links (bridges) formed between different chains make the rubber harder and stronger.