How do the monomers link to form the polymer of urethane?
Ethyl carbamate or urethane is the ethyl ester of carbamic acid (NH2COOH). Polyurethane is the linear polymer of ethyl carbamate monomer. The amine or substituted amine end of one monomer combines with the ester part of the other monomer to form a strong amide (–CONH–) linkage, with the elimination of one molecule of ethyl alcohol in the process. Formation of multiple amide linkages constitute a large polymeric structure, known as polyurethane. As a small molecule (ethyl alcohol) is eliminated in each stage, the result is a thermoset polymer progressing through a condensation reaction.