asymmetric tpx porous membranes for gas separation are prepared by wet , and dry / wet phase inversion methods . a casting polymer solution including tpx , a selected solvent and optionally a selected non - solvent , is casted on a support , and within 100 seconds after the casting step , the casted polymer is immersed in a coagulant to form a membrane . the formed membrane is extracted , dried and optionally heat treated .