A non-isocyanate route (NIR) of making polyureas of high molecular weight has been found through trans-ureation of N,N’-diphenyl-4,4′-methylene
(diphenyldiamines) and polymethylenepolyphenylenepolyamines, the molar ratio of acid to amine being not more than 0.2, B) reaction of the mixture obtained in step A) with phosgene to give methylene(diphenyl diisocyanates) and polymethylenepolyphenylene polyisocyanates, C) separation of the mixture ...