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JEE Main levelSingle correct optionDifficulty 2 of 3pl261

Natural rubber is a polymer of the monomer shown. When rubber is heated with sulfur, the percentage of sulfur determines the product. Which outcome is correct when the sulfur content is raised from about 3-5 percent to about 30 percent?

  1. AConversion into gutta-percha
  2. BA softer, stickier rubber
  3. CA thermoplastic that melts and can be remoulded
  4. DA hard, rigid, non-elastic material (ebonite)

Answer: D

Isoprene (2-methylbuta-1,3-diene) is the monomer of natural rubber. A few percent sulfur gives a soft, elastic vulcanised rubber, but around 30 percent sulfur creates so many crosslinks that the chains cannot move, giving hard, rigid, non-elastic ebonite. More crosslinking does not make the polymer softer, thermoplastic or trans.
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