Process for the preparation of complexes of one mol of dimerized or low-oligodimerized 4,4'-diisocyanatodiphenylmethane and two to three mol of 4,4'-diisocyanatodiphenylmethane, corresponding complexes, and their use for polyurethane production

摘要

The present invention relates to a process for the dimerization of 4,4'-diisocyanatodiphenylmethane from emulsion in apolar solvents with the formation of complexes and to the complexes obtainable for the first time by this process. The complexes consist of one mol of low molecular weight 4,4'-diisocyanato-diphenylmethane-uretdione or its low oligomers corresponding to the idealized formula (I) <IMAGE> (I) <IMAGE> (n=0 to 0.5, where n is the average degree of oligomerization of the dimer) and 2 to 3 mol of 4,4'-diisocyanatodiphenylmethane (MDI) <IMAGE> (II) In the process according to the invention, 4,4'-diisocyanatodiphenylmethane (II) in the molten form is emulsified in apolar solvents. Dimerization is started in the presence of conventional dimerization catalysts at temperatures above the melting point of MDI, preferably up to an upper temperature limit of 50 DEG to 60 DEG C. The temperature is then lowered to <40 DEG C. If desired, dimerization can be stopped when an isocyanate content of from 22.4 to 26.9% has been reached. The product is then worked up at low temperatures, preferably at 0 DEG to 25 DEG C. The complex obtained is claimed as a new substance. The use of the complex for the production of polyurethanes is also claimed.