Which one of the following polymers is not obtained by condensation polymerisation?

Condensation polymerisation is defined as a polymerisation process in which monomer units join together with the elimination of small molecules such as $$H_2O$$ or $$HCl$$.

Option A: Nylon-6,6 is prepared by the condensation of hexamethylenediamine and adipic acid with the elimination of $$H_2O$$. This fits the definition of condensation polymerisation.

Option B: Buna-N is a copolymer of 1,3-butadiene and acrylonitrile formed by addition polymerisation. In this process, monomers add to each other without elimination of any small molecule. Therefore, it is not obtained by condensation polymerisation.

Option C: Bakelite is formed by the condensation of phenol and formaldehyde with elimination of $$H_2O$$. This clearly is a condensation polymerisation.

Option D: Nylon-6 is produced by the ring-opening polymerisation of caprolactam. In this reaction no small molecule such as $$H_2O$$ is eliminated, yet in JEE classification it is grouped with condensation polymers because its repeating unit contains amide linkages.

Among the given options, the polymer not obtained by condensation polymerisation is Option B: Buna-N.