IMPROVEMENT IN COLOR OF POLYMER MDI

摘要

PROBLEM TO BE SOLVED: To provide a method for producing a polymethylenepolyphenyl polyisocyanate having improved discoloration. SOLUTION: This method for producing a polymethylenepolyphenyl polyisocyanate comprises phosgenating a corresponding polyamine solution in an inert organic solvent, removing excessive phosgene and stripping the solvent. At any point of time before the stripping process, at least 0.00015 wt.% of an additive based on 100 wt.% of a polyamine is added to the solution. The additive is hydrazine or a hydrazine derivative.