Terpolymerization of acrylamide (AM), acrylic acid (AA), and acryloyloxyethyl trimethylammonium chloride (DAC) was studied in aqueous solution by a two-step polymerization method, consisting of adiabatic polymerization until reaching a maximum temperature and following retaining temperature for maturation. A redox agent:promotor triad-initiating system was employed as an initiator. The effects of various parameters on terpolymerization were investigated. The optimum values were obtained at the DAC:AA molar feed ratio and the total monomer concentration, at the oxidant: reductant ratio and total redox agent concentration, and at the promotor concentration and redox agent:promoter ratio. The structure of the terpolymer was identified by Fourier transform infrared (FTIR) and C-13 NMR spectroscopy. And the terpolymer composition was agreed favorably with feed ratio. (c) 2006 Wiley Periodicals, Inc.