Hydrolysis of linear polyurethanes and model monocarbamates

Abstract

Abstract Alkaline hydrolysis of model carbamates, polyurethanes, and poly(urethane‐ureas) has been investigated. The model carbamates were based upon phenyl, benzyl, and cyclohexyl isocyanates. The polyurethanes and poly(urethane‐ureas) were prepared from tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4′‐dicyclohexylmethane diisocyanate (H 12 MDI) and a poly(oxyethylene)glycol of 6000 molecular weight. Pseudo‐first‐order rate constants of hydrolysis were obtained in aqueous pyridine solution at 110°C, and second‐order rate constants were obtained in aqueous KOH solution for the model biscarbamates. Pseudo‐first‐order rate constants of hydrolysis were obtained in alcoholic KOH solution for the polyurethanes and poly(urethane‐ureas). The hydrolysis of the model carbamates showed that the stability increased in the following manner: phenyl < benzyl < cyclohexyl. The pseudo‐first‐order rate constants were dependent upon the p K b of the corresponding amines. The hydrolysis of the polyurethanes and poly(urethane‐ureas) showed that the stability increased in the following manner: aromatic < aralkyl < cycloaliphatic. It was shown that polyurethanes are more susceptible to alkaline hydrolysis than to acidic hydrolysis.