Which of the following is not a condensation polymer?

We need to identify which polymer is NOT a condensation polymer.

Condensation polymers are formed by the condensation reaction between monomers, with the elimination of small molecules like water ($$H_2O$$) or hydrochloric acid ($$HCl$$).

Addition polymers are formed by the addition of monomers containing double bonds, without the loss of any small molecules.

Option A: Nylon-6,6 - Formed by the condensation of hexamethylenediamine and adipic acid, with elimination of water. This is a condensation polymer.

Option B: Nylon-6 - Formed by the ring-opening polymerization of caprolactam, which involves internal amide bond formation. This is classified as a condensation polymer.

Option C: Dacron (Polyethylene terephthalate, PET) - Formed by the condensation of ethylene glycol and terephthalic acid, with elimination of water. This is a condensation polymer.

Option D: Buna-S - This is a copolymer of 1,3-butadiene and styrene, formed by addition polymerization (free radical polymerization). No small molecule is eliminated during the process. This is an addition polymer, NOT a condensation polymer.

The correct answer is Option D: Buna-S.