Vulcanization involve the removal of

1. Analyze the question

The question asks for the chemical process that occurs during the vulcanization of rubber. Specifically, it asks what is removed or altered in the structure of the rubber polymer during this process.

2. Explain the concept

Vulcanization is a chemical process used to improve the physical properties of natural rubber (polyisoprene). Natural rubber is soft, sticky when hot, and brittle when cold.

Natural rubber consists of long polymer chains of isoprene units. These chains contain carbon-carbon double bonds (C=C). During vulcanization, sulfur is added to the rubber and heated. The sulfur atoms form "cross-links" (bridges) between the polymer chains.

To form these cross-links, the sulfur atoms must attach to the carbon atoms. This reaction involves the breaking of the carbon-carbon double bonds in the polymer chain, which allows the sulfur to bond to the carbon atoms and create a stable, cross-linked network.

3. Show the solution

• Step 1: Identify the structure of natural rubber: It is a polymer of isoprene, which contains unsaturated double bonds ($C=C$).
• Step 2: Understand the vulcanization reaction: Sulfur is introduced to cross-link the polymer chains.
• Step 3: Determine the chemical change: For the sulfur to form a bridge between two chains, the existing double bonds must be broken (saturated) so that the carbon atoms can form new single bonds with the sulfur atoms.
• Step 4: Conclusion: The process effectively removes the double bonds by converting them into single bonds as part of the cross-linking process.

4. Identify the answer

The correct option is C. Vulcanization involves the saturation of the double bonds in the polymer chain to create cross-links.

5. Exam Tip

Think of vulcanization as "stitching" together loose threads (polymer chains). To stitch them together, you have to "open up" the existing structure (the double bonds) to make room for the "thread" (the sulfur atoms). Remember: Vulcanization = Sulfur + Heat = Cross-linking = Breaking double bonds.