35.1.4—Monomer(s) present

To identify condensation monomers, cut each ester or amide link at the bond formed during condensation and restore the corresponding –OH/–COOH or –NH₂ groups.

An ester link points to a diol plus dicarboxylic acid (or a hydroxycarboxylic acid); an amide link points to a diamine plus dicarboxylic acid or amino acid family.

From –O–CH₂CH₂–O–CO–C₆H₄–CO–, restore ethane-1,2-diol and benzene-1,4-dicarboxylic acid.

Do not interpret every oxygen as an alcohol group; inspect whether it sits in –CO–O– or another linkage.