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 isa misnomer because it is not made by the polymerization of urethane. In commonwith condensation polymers, the name refers to the presence of urethane groupsin PUs as inter-unit linkage. The group is obtained in the polymer in thefollowing manner:

Though apparently polyurethaneformation is an addition reaction, the mode of formation, however, involvesstep growth mechanism only. That is, the polymeric chains are not formed allat once as in the case of true addition polymers; but only gradually asdimmers, trimers, tetramers, pentamers etc.



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Author is Faculty inFootwear Design Development Institute, Fursatganj, Raebareli.