PROCESS FOR THE PRODUCTION OF POLYISOCYANATES OF THE DIPHENYLMETHANE SERIES WITH A REDUCED COLOR VALUE

摘要

Polyisocyanates of the diphenylmethane series are produced by a) reacting aniline and formaldehyde in the presence of an acidic catalyst to produce a polyamine, b) neutralizing the reaction mixture from step a) with a base at a temperature of more than 110.degree.C or neutralizing the reacti on mixture from step a) with a base and heating the neutralized mixture to a temperature of more than 110.degree.C, and c) phosgenating the polyamine fro m step b) to convert it to the corresponding polyisocyanate.