A novel copolymer hydrogel, poly(acrylamide-co-diallyl dimethyl ammonium chloride), was prepared by the radical copolymerization of acrylamide and diallyl dimethyl ammonium chloride in an ionic liquid (IL)-water binary system in the presence of the crosslinker N,N'-methylene bisacrylamide. The equilibrium swelling ratios of the hydrogels synthesized in the M-water binary system increased with the content of IL and were remarkably higher than that of the gel synthesized in water. Differential scanning calorimetry measurements showed that the glass-transition temperatures of the dry hydrogels that were synthesized in the IL-water binary system were remarkably lower than that of the gel synthesized in pure water. The mechanical properties of the gels synthesized in both water and the IL-water binary system were characterized with a universal material-testing machine. The results show that fracture toughness of the hydrogels was improved when they were synthesized in the IL-water binary system. The gel shrank under a direct-current electric field. The response rates of the gels that were synthesized with the IL-water binary system were faster than that of the gel synthesized in water. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2940-2945, 2010