Process for the preparation of polyisocyanates of the diphenylmethane series having reduced colour

摘要

A method for the production of polyamines of the diphenylmethane series involves acid-catalyzed reaction of aniline with formaldehyde. The reaction mixture is neutralized with a base at above 110 degrees C, or heated to above 110 degrees C after neutralization with a base. An Independent claim is also included for a method for the production of polyisocyanates of the diphenylmethane series, by phosgenation of the polyamines obtained by the new method.