Condensation polymerization

Condensation polymerization is different from addition polymerization in two ways: 1) the reaction needs no initiator to start, and 2) a small molecule, e.g., water, forms as a by-product. Polyesters (e.g., PET) and polyamides (e.g., nylon) are condensation polymers, where two monomer types connect alternatingly.

In the case of nylon, a molecule with two amine groups reacts with a molecule with two carboxylic acid groups. During the reaction, amide groups form while ejecting water.

Figure 1: Condensation polymerization between an amine group and a carboxylic group, forming an amide linkage.