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Polymers question

2016 · Shift 1 · Q16
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Polymers question

2016 · Shift 1 · Q16

JEE AdvancedChemistryPolymersMCQ+3 / −1
On complete hydrogenation, natural rubber produces
  1. A
    ethylene-propylene copolymer.
  2. B
    vulcanized rubber.
  3. C
    polypropylene.
  4. D
    polybutylene.
View written solutionFree

Correct answer: A

  1. Identify the structure of natural rubber

Natural rubber is cis-1,4-polyisoprene.

The monomer is isoprene: Isoprene=CH2=C(CH3)−CH=CH2\text{Isoprene} = \text{CH}_2=C(CH_3)-CH=CH_2Isoprene=CH2​=C(CH3​)−CH=CH2​

On polymerization, natural rubber has repeating unit: [−CH2−C(CH3)=CH−CH2−]n[-CH_2-C(CH_3)=CH-CH_2-]_n[−CH2​−C(CH3​)=CH−CH2​−]n​

  1. What does complete hydrogenation do?

Complete hydrogenation adds hydrogen across all the double bonds, converting each C=CC=CC=C into C−CC-CC−C.

So, [−CH2−C(CH3)=CH−CH2−]n→complete hydrogenation[−CH2−CH(CH3)−CH2−CH2−]n[-CH_2-C(CH_3)=CH-CH_2-]_n \xrightarrow[\text{complete hydrogenation}]{} [-CH_2-CH(CH_3)-CH_2-CH_2-]_n[−CH2​−C(CH3​)=CH−CH2​−]n​complete hydrogenation​[−CH2​−CH(CH3​)−CH2​−CH2​−]n​

  1. Recognize the resulting polymer

The saturated repeating unit is: [−CH2−CH(CH3)−CH2−CH2−]n[-CH_2-CH(CH_3)-CH_2-CH_2-]_n[−CH2​−CH(CH3​)−CH2​−CH2​−]n​

This can be viewed as a copolymer chain made up of alternating ethylene and propylene type units. Hence, the hydrogenated product is ethylene-propylene copolymer.

  1. Check the options
  • A: ethylene-propylene copolymer — Correct.
  • B: vulcanized rubber — Incorrect; vulcanization involves sulfur cross-linking, not hydrogenation.
  • C: polypropylene — Incorrect; polypropylene has repeating unit [−CH2−CH(CH3)−]n[-CH_2-CH(CH_3)-]_n[−CH2​−CH(CH3​)−]n​, which is different.
  • D: polybutylene — Incorrect; structure does not match.
  1. Final answer

Therefore, on complete hydrogenation, natural rubber produces ethylene-propylene copolymer.

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