TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The crosslinking treatment is selected from chemical crosslinking and UV radiation. The method further involves coating a top surface of the polymer membranes made from aromatic polyimide membranes by thermal treating and UV crosslinking with a thin layer of high permeability material selected from a polysiloxane, a fluoro-polymer, a thermally curable silicone rubber, and a UV radiation curable epoxy silicone. Preferred Components: The polyimide polymer comprises repeating units of a formula (I). The 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(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-2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane-3,3'-dihydroxy-4,4'-diamino-biphenyl) (poly(DSDA-APAF-HAB)), poly(2,2'-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride-3,3',4,4'-benzophenonetetracarboxylic dianhydride-2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane) (poly(6FDA-BTDA-APAF)), poly(4,4'-oxydiphthalic anhydride-2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane) (poly(ODPA-APAF)), 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 poly(4,4'-bisphenol A dianhydride-3,3',4,4'-benzophenonetetracarboxylic dianhydride-2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane) (poly(BPADA-BTDA-APAF)).X1-=group of formula (i)-(iii);X2=X1 or group of formula (iv)-(xi);Y'=group formula (xii)-(xiv);andZ', Z'', and Z'''=-O- or -S-;R=-C(CF3)2-, -C(CH3)2-, -SO2-, -O-, -S-. EXAMPLE - A three-neck round-bottom flask equipped with a nitrogen inlet and a mechanical stirrer was charged with 3,3',4,4'-benzophenonetetracarboxylic dianhydride (APAF) (10 g)and N-methylpyrrolidone (NMP) (40 ml). Once the APAF was fully dissolved, a solution of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane diamine (BTDA) (8.8 g) in NMP (40 ml) was added to the APAF solution in the flask. The reaction mixture was mechanically stirred for 24 hours at ambient temperature to give a viscous poly(amic acid) solution. Then acetic anhydride (11.1 g) in NMP (10 ml) was added slowly to the reaction mixture under stirring followed by the addition of pyridine (8.6 g) in NMP (10 ml) to the reaction mixture. The reaction mixture was mechanically stirred for an additional 1 hour at 80 degrees C to yield the poly(BTDA-APAF) polyimide. A poly(BTDA-APAF) polyimide (4 g) was dissolved in a solvent mixture of NMP (12 g) and 1,3-dioxolane (12 g). The mixture was mechanically stirred for 2 hours to form a homogeneous casting dope. The resulting homogeneous casting dope was allowed to degas overnight. The poly(BTDA-APAF) polymer membrane was prepared from the bubble free casting dope on a clean glass plate using a doctor knife with a 20-mil gap. The membrane together with the glass plate was then put into a vacuum oven. The solvents were removed by slowly increasing the vacuum and the temperature of the vacuum oven. Finally, the membrane was dried at 200 degrees C under vacuum for at least 48 hours to completely remove the residual solvents to form poly(BTDA-APAF) polymer membrane.