Copolymer particles consisting of acrylamide (AM) and cationic comonomer 2-methyl acryloyloxyethyl trimethyl ammonium chloride (DMC) were prepared by precipitation polymerization in an solution of potassium citrate using ammonium persulfate ((NH4)(2)S2O8) and sodium sulfite (Na2SO3) as an initiator. The product poly(acrylamide-2-methyl acryloyloxyethyl trimethyl ammonium chloride) [Poly(DMC-AM)] is a water-soluble cationic polyelectrolyte. The solubility of DMC, AM and Poly(DMC-AM) in potassium citrate solution were measured, combined with the theory of solubility parameter, and the experiment results indicate that the solubility of DMC and AM is much higher than that of Poly(DMC-AM), and also the mechanism of copolymer precipitated in salt solution was discussed. The factors influencing the conversion of comonomers were examined, such as salt mass fraction, polymerization temperature, monomers mass fraction, initiator mass fraction, and so on. The results of experiments indicate that the best conditions are salt mass fraction = 57%, monomers mass fraction = 3%, m(DMC) : m(AM) = 3 : 1, initiator mass fraction = 0.08%, polymerization temperature = 50 degrees C, reaction time = 2 h, and the conversion is 86.4%. And the qualitative analysis experimental method for copolymer by infrared absorption spectrum show that [Poly(DMC-AM)l was successfully synthesized by precipitation polymerization. (c) 2007 Wiley Periodicals.