Toluene diisocyanate $(TDI)$ is used in the synthesis of which polymer?

The structures of some important polymers are given. Which one represents Buna-$S$?

Isoprene is a valuable substance for making

Which of the following polymers is used in the preparation of gaskets?

In polymer Buna-$S$,'$S$' stands for :-

If $\bar{M}_w$ is the weight average molecular weight and $\bar{M}_n$ is the number average molecular weight of a polymer, the poly dispersity index $(PDI)$ of the polymer is given by