Explain the process of vulcanization of rubber.

(N/A) Natural rubber becomes soft at high temperatures $( >335 \ K)$ and brittle at low temperatures $( < 283 \ K)$ and shows high water absorption capacity. It is soluble in non-polar solvents and is non-resistant to attack by oxidizing agents.
To improve upon these physical properties,a process of vulcanization is carried out. This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between $373 \ K$ to $415 \ K$. On vulcanization,sulphur forms cross-links at the reactive sites of double bonds and thus the rubber gets stiffened.
In the manufacture of tyre rubber,$5 \%$ of sulphur is used as a cross-linking agent. The probable structures of vulcanized rubber molecules are shown below:
(Structure Image: $939-$s48)