Membranes of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)-2,3,5,6-tetramethyl-1,4-phenylene diamine (TeMPD) polyimide, a fluorine-containing polyimide synthesized using 6FDA and TeMPD, were modified by immersing them in various amino compound solutions for application in artificial lungs. Permeabilities of dried gases (P-G) and gases dissolved in water (P-L) through the membranes were investigated. The surface reaction ratios of all the modified membranes were higher than the total reaction ratio, indicating that the modified membranes exhibited graded structures that were reacted with amino compounds from both surfaces toward the interior. Both P-L (O-2) and P-L (CO2) of the base membrane and amine-modified membranes, except the membrane where D-glucamine was used, were lower than or equal to P-G (O-2) and P-G (CO2), respectively. Both P-L (O-2) and P-L (CO2) of the amine-modified membranes decreased with increasing water content, which suggests that water content strongly affected permeability in liquid phase. Results indicate that water molecules interrupted gas permeation. Moreover, CO2/O-2 permselectivity in liquid phase increases with high-polarity amino compounds compared with the base membrane. (C) 2015 Society of Plastics Engineers