TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The molar ratio of the compound (ii) (preferably 4,4'-dimethylbiphenyl-3,3'-diol and 4,4'-dimethylbiphenyl-3,3'-diyl diacetate) to compound of formula (v) (preferably 4,4'-(perfluoropropane-2,2-diyl)bis(2-methylphenol) and 4,4'-(perfluoropropane-2,2-diyl)bis(2-methyl-4,1-phenylene) diacetate) is 1:2 to 1:5 (preferably 1:4).    TECHNOLOGY FOCUS - POLYMERS - Preferred Membrane: The blend membrane (R1) comprises polymer containing aromatic sulfonic acid groups (0.05-20 wt.%). The blend membrane (R1) is in a configuration selected from flat sheet, disk, tube, and hollow fiber. The blend membrane (R1) is converted to polybenzoxazole membrane by thermally treating the gas separation membrane. Preferred Components: The polymer containing aromatic sulfonic acid groups is selected from poly(styrene sulfonic acid), and poly(trifluorostyrene sulfonic acid). The aromatic polyimide polymer is selected from poly(3,3',4,4'-benzophenonetetracarboxylic dianhydride-2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane) (poly(BTDA-APAF)), poly(3,3',4,4'-benzophenonetetracarboxylic dianhydride-3,3'-dihydroxy-4,4'-diamino-biphenyl) (poly(BTDA-HAB)), poly(4,4'-oxydiphthalic anhydride-2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane) (poly(ODPA-APAF)), poly(3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride-2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane) (poly(DSDA-APAF)), poly(3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride-3,3'-dihydroxy-4,4'-diamino-biphenyl) (poly(DSDA-HAB)), poly(4,4'-oxydiphthalic anhydride-2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane-3,3'-dihydroxy-4,4'-diamino-biphenyl) (poly(ODPA-APAF-HAB)), poly(3,3',4,4'-benzophenonetetracarboxylic dianhydride-2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane-3,3'-dihydroxy-4,4'-diamino-biphenyl) (poly(BTDA-APAF-HAB)), and/or poly(4,4'-bisphenol A dianhydride-3,3',4,4'-benzophenonetetracarboxylic dianhydride-2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane) (poly(BPADA-BTDA-APAF)). Preferred Definitions:    X1=bis-(3,4-dimethyl-phenyl)-methanone;    X2=4,4'-(perfluoropropane-2,2-diyl)bis(2-methylphenol) or 4,4'-(perfluoropropane-2,2-diyl)bis(2-methyl-4,1-phenylene) diacetate;    R'=1,1,1,3,3,3-hexafluoro-2,2-dimethyl-propane.    EXAMPLE - A blend polymer membrane comprising: poly(6FDA-HAB) (containing 2,2'-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride and 3,3'-dihydroxy-4,4'-diamino-biphenyl) (2.5 g), poly(BTDA-APAF-HAB) (containing 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and 3,3'-dihydroxy-4,4'-diamino-biphenyl) (2.5 g), N-methylpyrrolidone (16 g) and 1,3-dioxolane (9 g) was prepared.