Color reduction of polymeric isocyanates via multiple solvent fractionation

摘要

Disclosed is an extraction process wherein a crude polyisocyanate is separated into a purified fraction and residual fraction wherein the purified fraction is characterized by greatly improved color over the crude material but with little or no difference in viscosity. The residual fraction remains perfectly useful for those applications where color is not a critical requirement. Significantly, the disclosed purification is achieved with literally a 100 percent material balance. No loss in polyisocyanate is encountered.