Besides the polymer, what else is formed during condensation polymerisation?

During the process of condensation polymerisation, along with the formation of a polymer, a small molecule such as water (H₂O) or hydrochloric acid (HCl) is produced. This is a key characteristic of condensation reactions, where two monomer units combine with the elimination of a small molecule. The polymer itself is formed from the repeated units of the monomers, while the small molecule forms as a by-product of the reaction that links these units together.

This phenomenon occurs because the functional groups on the monomers react to form the polymer's backbone, and during this reaction, the small molecule is expelled. For example, when carboxylic acids react with alcohols, water is produced when they form esters. This aspect of condensation polymerisation distinguishes it from other types of polymerisation, such as addition polymerisation, where no by-products are formed.

Other options like carbon dioxide or a metal ion do not typically emerge from the condensation polymerisation process. Carbon dioxide might be produced in certain biochemical or combustion reactions, while metal ions are not relevant to the general context of polymerisation involving organic molecules. Alkenes could form through different types of reactions, but not during the straightforward condensation of functional groups in this polymerisation context.