Monomer reactivity ratios of acrylonitrile/ammonium itaconate during aqueous-deposited copolymerization initiated by ammonium persulfate were investigated. Kelen-Tudos method was used to examine the reactivity ratios. It was shown that the reactivity ratios were influenced by the conversions and temperatures of copolymerization. The reactivity ratios in aqueous-deposited copolymerization system were similar to those in the solution polymerization system at polymerization conversions of less than 5% [reactivity ratio of acrylonitrile (r(1)) 0.842 +/- 0.02, reactivity ratio of ammonium itaconate (r(2)) = 3.624 +/- 0.02]. The reactivity ratio of AN rises and that of (NH4)(2)IA decreases, when the polymerization conversion increases till 13%, Aqueous-deposited copolymerization initiated by AIBN was also studied. It was found that some polymers were formed in water phase and the monomers had different reactivity ratios by comparison with those initiated by ammonium persulfate. (c) 2006 Wiley Periodicals, Inc.