amine is used in the reaction as it permits the formation of a disubstituted amino acid, i.e. a monofunctional amine having two acid groups which then can be converted to the ammonium salt. Generally, the amines are lower alkyl amines
having from 1 to 15 carbon atoms, and preferably 1 to 3 carbon atoms, lower alkanolamines where the alkanol portion has from 2 to 4 carbon atoms; phenyl amines such as mono and dibenzylamine, cyclic amines such as cyclohexylamine and dicyclohexylamine; aralkyl amines, e. g. ethylbenzylamines and so forth. The amines can be substituted with various functional groups so long as the functionality does not interfere with the reaction or impart an adverse characteristic to the resulting polyurethane resin.