The polymerization kinetics of acrylonitrile (AN) with the potassium persulfate (K2S2O8)/thiourea redox system has been investigated volumetrically in an aqueous medium in the temperature range of 40-80 degrees C. The rate of polymerization (R-p) and rate of K2S2O8 disappearance have been measured. The effects of some water-miscible organic solvents, cationic, anionic, nonionic surfactants, and cornplexing agents on the Rp were investigated. The temperature dependence of the rate was studied, and the activation parameters were computed using the Arrhenius and Eyring plots. The effects of organic solvents on polymerization were also investigated. All of them depressed both the initial rate and limiting conversion. A mechanism consistent with the experimental data involving K2S2O8-thiourea complex formation, which generates free radicals, is suggested. Molecular weight of the polymer was determined by viscometry. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3395-3400, 2008