| abstract |
The invention relates to a process for the preparation of polyisocyanate mixtures containing at least 90 wt .-%, based on the polyisocyanate mixture, a mixture of ai) diphenylmethane diisocyanate and aii) Triphenylendimethylentriisocyanat, wherein the mixture a) at least 2 wt .-%, based to the weight of the polyisocyanate mixture, triphenylendimethylene triisocyanate, comprising the steps A) conversion of aniline and formaldehyde to a mixture of diphenylmethanediamine and its higher homologs, B) reaction of the mixture from step a) with phosgene and separation of the volatile compounds from the reaction product, C) separation of diphenylmethane diisocyanate and triphenylendimethylene triisocyanate from the product obtained in step B). |