Abstract: The permeability coefficients of five 6FDA-based polyimide membranes to H₂, CO₂, O₂,N₂, and CH₄ have been meassured at 0.6MPa and 30℃. Differences in chemical structure were found to lead to a significant change in permeability coefficients and were related to the ideal separation factotes of smaller penetrant molecules against biger ones. For polyimides 6FDA-DABP, 6FDA-ODA, 6FDA-MDA and 6FDA-IPDA, the increase in permeability coefficents was accompanied with the decrease of the ideal separation factors. Having the bulky methyl side groups on the aromatic rings of DMMDA, polyimide 6FDA-DMMDA possesses both high P_H2 and high α_H2/N2 and α_H2/CH₄. The favorable permseleetivity, excellent thermal and mechanical durability, and good processability make 6FDADMMDA a promising candidate material for gas separation.

Key words: polyimide, gas separation, membrane, gas permeability