Concept:Addition polymers are formed by repeated addition of unsaturated monomers, while condensation polymers form by linking monomers with the loss of small molecules.Explanation:nylon is a polyamide made from dicarboxylic acid and diamine monomers.It forms through condensation polymerization, not addition polymerization.perspex, polyethene, and polychloroethene are all formed from alkene-type monomers by addition polymerization.Hence, nylon is the substance that is not an addition polymer.Answer:A. nylon