Process for preparing polyimides end-capped with anhydride or isocyanate groups

Claim 1

In the process of preparing a polyimide of the formula: ##STR13## by the reaction of an aromatic dianhydride of the formula: ##STR14## with an aromatic diisocyanate of the formula OCN--Ar--CNO; wherein Ar' is a tetravalent aromatic organic radical, the four carbonyl groups being attached directly to separate carbon atoms and each pair of carbonyl groups being attached to adjacent carbon atoms in the Ar' radical except that in the case of the Ar' being a naphthalene radical one or both pairs of the carbonyl groups may be attached to peri carbon atoms; Ar is a divalent aromatic radical; n is an integer of at least one; D is a radical selected from the group consisting of O< and >N--AR--NCO; and D' is a radical selected from the group consisting of OC< and ##STR15## the improvement comprising the reaction of said aromatic dianhydride and said aromatic diisocyanate while in intimate contact with each other and with a metal acetylacetonate in which said metal is selected from the class consisting of Al, Co, Fe, Ni and Zr, the temperature of said reaction being in the range of 70°-150° C. and the amount of said metal acetylacetonate being in the range of 0.005-1 gram per equivalent weight of aromatic dianhydride.