A series of imidazolium-based ionic liquid monomers and their corresponding polymers (poly(ionic liquid)s) were synthesized, and their CO2 sorption was studied. The poly(ionic liquid)s had enhanced CO2 sorption capacities and fast sorption/desorption rates compared with room temperature ionic liquids. The effects of the chemical structures, including the types of anion, cation, and backbone of the poly(ionic liquid)s on their CO2 sorption have been discussed. In contrast to room temperature ionic liquids, the polymer with PF6-anions had the highest CO2-sorption capacity, while those with BF4- or Tf2N- anions had the same capacities. The CO2 sorption and desorption of the polymers were fast and reversible, and the sorption was selective over H-2, N-2, and O-2. The measured Henry's constants of P[VBBI][BF4] and P[MABI][BF4] were 26.0 bar and 37.7 bar, which were lower than those of similar room temperature ionic liquids. The preliminary study of the mechanism indicated that the CO2 sorption of the polymer particles was more absorption (the bulk) but less adsorption (the surface). (c) 2005 Wiley Periodicals, Inc.