NOVELTY - Composition (I) comprises: a polymerized imidazolium room-temperature ionic liquid (RTIL); and an unpolymerized imidazolium RTIL, where the unpolymerized RTIL is at least 5 mole% of the total RTIL of the composition.    USE - (I) is useful in membrane for separating a first gas component from a gas mixture containing at least a first and a second gas component, where the first gas component is carbon dioxide and the second gas component is methane or nitrogen (all claimed). (I) is useful in catalysis, as antistatic agents, and for the removal of heavy metals from water.    ADVANTAGE - (I) imparts good antistatic characteristics and is compatible to a wider range of substrates. (I) is less corrosive. (I) provide membrane with improved mechanical stability and structural stability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a membrane comprising (I), where the membrane has a thickness of less than 500 nanometers;    (2) separating a first gas component from a gas mixture containing at least a first and a second gas component, comprising providing the membrane having a feed and a permeate side, where the membrane is selectively permeable to the first gas component over the second gas component; applying a feed stream including the first and the second gas components to the feed side of the membrane; and providing a driving force sufficient for permeation of the first gas component through the membrane, hence producing a permeate stream enriched in the first gas component from the permeate side of the membrane;    (3) imidazolium salts of formula (A);    (4) a polymer membrane comprising many diol-functionalized imidazolium repeating unit of formula (A1); and    (5) a composite membrane comprising a porous support and a RTIL polymer embedded within the pores of the support, where the RTIL polymer comprising many diol-functionalized imidazolium repeating units (A1).    X- = anion comprising (bistrifluoromethylsulfonyl)imide ion (preferred), halide ion, hexafluorophosphate ion, tetrafluoroborate ion, dicyanamide ion, sulfonated ion or fluorinated sulfonated ion;    R2 = H or CH3; and    R3 = CH3, ethyl, propyl, butyl, benzyl, ethenyl (vinyl) or styrene.