... HOOC-R-COOH + H2N-R'-NH2 + HOOC-R-COOH + H2N-R'-NH2 ...
(becomes:)
...-R-CO-NH-R'-NH-CO-R-CO-NH-R'-NH-... + nH2O
The carboxylic acids and amines link to form peptide links, also known as amides. Proteins are polymers containing the peptide links, the monomers being amino acids.
The industrial preparation of nylon from a diamine and dicarboxylic acid is quite slow.
In biology, biopolymers are a form of condensation polymers.