Process for producing porous aromatic polyimide membranes

摘要

A porous membrane of an aromatic polyimide having an enhanced permeability of a gas or liquid is produced by a process comprising the steps of (1) preparing a dope solution of 3 to 30% by weight of an aromatic polyimide in a mixed solvent of (A) 100 parts by weight of a base solvent capable of dissolving 5% by weight or more of the polymeric acid and of evaporating at 30 DEG C. to 400 DEG C. and (B) 5 to 150 parts by weight of an additional liquid not capable of dissolving 3% by weight or more of the polyamic acid and capable of evaporating at a smaller evaporating rate than that of the base solvent at the above-mentioned evaporating temperature; (2) forming a thin layer of the dope solution at 0 DEG C. to 120 DEG C.; and (3) heating the dope solution layer at 30 DEG C. to 400 DEG C. so as to evaporate off the mixed solvent and to convert the polyamic acid to the corresponding polyimide.