TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: (I) comprises the polymerized RTIL having the structure of formula (1a) and unpolymerized RTIL having the structure of formula (2a) (5-60 (preferably 15-25) mol.%).R1-R4 = 1-20C alkylene, 1-20C alkenylene, 1-20C alkynylene or 1-20C arylene, preferably at least one of R3 and R4 is methyl, a carbon atom in at least one of R1-R4 is substituted, at least one of R1-R4 contains one or more hydroxyl groups, R1 is -(CH2)5-, -(CH-CH(OH)-CH2-OH) or -CH2-, R2 is -(CH2)5-, R3 is CH3 and R4 is ethyl or hexyl;Y1, Y2, Z1-Z4 = H, 1-12C alkyl, 1-12C alkenyl or 1-12C alkynyl, where Y1 and Y2 are preferably H or CH3, and Z1-Z4 are preferably hydrogen;n = 2-100000; andX1, X2 = anion.Preferred Components: The polymerized RTIL comprises many RTIL-based repeating units of formula (3a), where the number of repeating units in the RTIL polymer is 2-100000. The polymerized RTIL has the structure of formula (4a) or (5a). Preferred Components: The membrane has a thickness of less than 200 nanometers. The membrane comprises a first layer and an opposing second layer comprising the polymerized RTIL, where the unpolymerized RTIL is between the first and second layer. The membrane has carbon dioxide permeability of 40 barrers or greater, preferably 16-44 barrers. The membrane has a carbon dioxide/methane (CO2/CH4) separation selectivity of 20 or greater, preferably 40 or greater. The membrane has a surface resistivity of 4.9x 109 ohms/cm2 or greater at a 10 volt potential, or 4.2x 109 ohms/cm2 or greater at a 100 volt potential. The thickness of the membrane is 50 nm-200 mu m. The membrane further comprises repeating crosslink units and the ratio of crosslink repeating units to diol-functionalized imidazolium repeating units is greater than zero and less than or equal to 5%. The support is a hydrophilic polymeric support, preferably polysulfone support. The thickness normalized water vapor flux of the membrane is 100-200 kg m-2 day-1 mu m. EXAMPLE - No suitable example given.