Polyimide membranes made of polymerization solutions

A process for producing a polyimide hollow fiber membrane, the process comprising:

• (a) forming a polyimide solution comprising an aprotic dipolar solvent and a polyimide;
• (b) filtering and devolatizing the polyimide solution to obtain a casting solution;
• (c) pumping the casting solution through a two material die together with a bore solution to produce a polyimide hollow fiber by phase inversion;
• (d) treating the polyimide hollow fibers with a dry thermostated gas before entry into an aqueous coagulation bath to produce treated hollow fibers;
• and
• (e) dipping the treated hollow fibers into the aqueous coagulation bath to produce the polyimide hollow fiber membrane;
• wherein the polyimide is obtained by polymerization of an aromatic dianhydride and an aromatic diisocyanate from a reaction mixture comprising the aprotic dipolar solvent and 0.01 to 5% by weight of a basic catalyst, calculated on the combined amount of aromatic dianhydride, and aprotic dipolar solvent, and has not been isolated as a solid material and then redissolved prior to forming said polyimide solution.