Which of the following is not a condensation polymer?

(a) Nylon$- 6, 6$ is the polymer of hexamethylene diamine and adipic acid. It is made by the condensation of given monomers.

(b) Nylon$- 6$ os also a condensation polymer of caprolactum. It is a polymide.

(c) Dacron is also a condensation polymer of ethylene glycol and terephthalic acid. It is an example of polyester.

(d) Buna$- S$ is an addition polymer of $1, 3,$ butadiene and styrene.

Hence, only (4) is not a condensation polymer.

$∴$ (4) is the correct option.