Urethane is the trivial name of carbamic acid NH2.CO.OH amino derivative of carbonic acid, HO.CO.OH (ie.H2CO3). For polyurethanes (PU), this name is a misnomer because it is not made by the polymerization of urethane. In common with condensation polymers, the name refers to the presence of urethane groups in PUs as inter-unit linkage. The group is obtained in the polymer in the following manner:
Though apparently polyurethane formation is an addition reaction, the mode of formation, however, involves step growth mechanism only. That is, the polymeric chains are not formed all at once as in the case of true addition polymers; but only gradually as dimmers, trimers, tetramers, pentamers etc.
Author is Faculty in Footwear Design Development Institute, Fursatganj, Raebareli.