JPS5854841B

A selective permeable membrane and a process for preparing the membrane. The process comprises applying to a supporting substrate a membrane forming solution prepared by dissolving in an organic solvent a polyimide polymer comprising principally a repeating unit represented by the general formula (I): (I) wherein R1 represents a divalent organic group, and a liquid swelling agent having a coagulation value with respect to the polyimide polymer of about 50 to about 200 and a boiling point of about 50 DEG C. to about 120 DEG C. under atmospheric pressure, evaporating at least a part of the swelling agent, and coagulating the polyimide polymer by contacting the polyimide polymer with a coagulating solvent which does not dissolve the polyimide polymer but is compatible with the organic solvent and the swelling agent.