A natural linear polymer of $2$-methyl-$1$, $3$-butadiene becomes hard on treatment with sulphur between $373$ to $415 \mathrm{K}$ and $—\mathrm{S}—\mathrm{S}—$ bonds are formed between chains. Write the structure of the product of this treatment?

2. Types of Polymerisation Reactions:

There are two broad types of polymerisation reactions, i.e., the addition or chain growth polymerisation and condensation or step growth polymerisation.

3. Natural rubber:

Rubber is a natural polymer and possesses elastic properties. It is also termed as elastomeric polymer. In elastomeric polymers, the polymer chains are held together by the weak intermolecular forces.

4. Synthetic rubbers:

Neoprene, Buna-S and Buna-N are examples of synthetic rubbers.

5. Biodegradable Polymers:

(i) Poly $\mathrm{\beta }$-hydroxybutyrate – co-$\mathrm{\beta }$-hydroxy valerate (PHBV): It is obtained by the copolymerisation of $3$-hydroxybutanoic acid and $3$ - hydroxypentanoic acid.

(ii) Nylon $2$–nylon-$6$: It is an alternating polyamide copolymer of glycine and amino caproic acid and is biodegradable.