In addition to the preferred 4,4'-methylene-bis-(cyclohexyl isocyanate), other useful dinuclear cyclic aliphatic diisocyanates are those which are formed through an alkylene group of from 1 to 3 carbon atoms inclusive, and which can be substituted with nitro, chlorine, alkyl, alkoxy and other groups which are not reactive with hydroxyl groups (or active hydrogens) providing they are not positioned