Patent ID: 6444777
Filing Date: 2002-09-03
Classification: C08G,C08J

Abstract:
A process for producing polyurethane elastomers comprising the steps of:a) forming a first prepolymer having a free NCO of from 0.05 to 8.0 weight % by reacting a polyhydroxyl compound having a molecular weight of from 800 to 6000 and selected from the group consisting of polyester polyols, hydroxyl-containing polycarbonates, and polyoxyalkylene polyols with a mixture of 3,3â€²-dimethylbiphenyl 4,4â€²-diisocyanate and a stoichiometric excess of at least one other diisocyanate selected from the group consisting of diphenylmethane diisocyanates; 1,2-diphenylethane diisocyanate; phenylene diisocyanate; aliphatic diisocyanates having from 4 to 12 carbon atoms; and cycloaliphatic diisocyanates having from 6 to 18 carbon atoms; b) forming a second prepolymer having a free NCO of from 3.3 to 10.0 weight % by reacting the first prepolymer with an additional amount of 3,3â€²-dimethylbiphenyl 4,4â€²-diisocyanate, wherein the equivalence ratio of the hydroxyl groups to the NCO groups of the at least one other diisocyanate to the NCO groups of the 3,3â€²-dimethylbiphenyl 4,4â€²-diisocyanate is 1:greater than 1 to 6:0.02 to 6; and c) reacting the second prepolymer with an additional amount of the polyhydroxyl compound, a hydroxyl-containing chain extender, a hydroxyl-containing crosslinker, or mixtures thereof to thereby form a polyurethane elastomer.