Abstract: Polyurethane prepolymers are disclosed prepared with mononuclear aromatic diisocyanate such as toluene diisocyanate and an aliphatic diisocyanate such as H12MDI. These prepolymers can be cured with 4,4'-methylene-bis-(3-chloro-2,6-diethylaniline) to form a cured urethane elastomer with reduced propensity to crack during the curing process, extended pour life (a slower rate of viscosity buildup after curative and prepolymer are mixed), low hysteresis, and a low level of free toluene diisocyanates and/or other toxic or volatile substances to increase worker safety during processing. It has also been found that prepolymers made from toluene diisocyanate and cured with a blend of two aromatic diamine curatives yields urethane elastomers with the same reduced propensity to crack during the curing process.

Abstract: A process for reducing the amount of residual organic diisocyanate monomer in a polyurethane prepolymer reaction product mixture which comprises distilling the polyurethane prepolymer reaction product mixture in the presence of a combination of at least one inert first solvent with a boiling point below the boiling point of the residual organic diisocyanate monomer and at least one inert second solvent with a boiling point above the boiling point of the residual organic diisocyanate monomer, at a temperature which exceeds the vaporization temperature of the residual organic diisocyanate monomer and which is below the decomposition temperature of the polyurethane prepolymer.