Gas‐permeation properties of asymmetric polycarbonate, polyestercarbonate, and fluorinated polyimide membranes prepared by the generalized dry–wet phase inversion process

Essentially defect‐free, ultrathin asymmetric polycarbonate, polyestercarbonate, and 6FDA–IPDA polyimide membranes were prepared by a dry/wet phase inversion process using forced‐convective evaporation. The pure gas permeation properties of these membranes were determined for N₂, O₂, He, CO₂, and CH₄. The average apparent skin‐layer thicknesses of the membrane samples varied between 330 and 580 Å, which is substantially thinner than for previous defect‐free membranes formed by the conventional wet phase inversion process. This study indicates that the dry/wet phase inversion process appears to be universally applicable to form ultrathin, defect‐free asymmetric membranes from hydrophobic, glassy polymers. © 1992 John Wiley & Sons, Inc.