35.1.1—Formation of polyesters

A diol and a dicarboxylic acid (or dioyl chloride) can link repeatedly through ester bonds, releasing water or HCl. A hydroxycarboxylic acid can self-condense in the same way.

Each monomer must have two reactive groups to extend the chain. The repeating unit contains the ester linkage –CO–O– and the polymer’s end groups depend on stoichiometric balance.

Ethane-1,2-diol plus benzene-1,4-dicarboxylic acid gives a chain containing –OCH₂CH₂OCOC₆H₄CO– repeats.

A single alcohol plus a single acid makes a small ester, not a polyester; chain growth requires at least two functional groups on each linking unit.