The free radical polymerization kinetics of the isomer sodium salts of o- and p-methacryloylaminophenylarsonate in aqueous solution have been studied using a dilatometric method. The polymerizations, initiated with potassium persulfate, were carried out at a constant monomer initial concentration of 0.50 mol/L and the initiator initial concentration was fixed at one of the following: 1.00, 2.00, 5.00, 8.00, or 10.00 (x 10(-3) mol/L). Another set of polymerizations were carried out at a constant initiator initial concentration of 2 x 10(-3) mol/L and the monomer initial concentration was fixed at one of the following: 0.20, 0.30, 0.50, 0.70, or 1.00 (mol/L). The polymerization reactions were conducted isothermally at 70degreesC. The order with respect to initiator was consistent with the classical kinetic rate equation, while the order with respect to monomer was greater that unity. The effects of temperature on the polymerization rate were also investigated and the activation energy gave values of 20.66, 22.68, and 23.22 kcal mol(-1) K-1 over a temperature range of 50-70degreesC. For the case of o-methacryloylaminophenylarsonic acid monomer, its kinetic study was carried out in DMF as solvent and AIBN initiator. p-Methacryloylaminophenylarsonic acid was too insoluble in DMF to be studied. The polymers obtained were characterized by H-NMR, IR, and viscosity. (C) 2004 Wiley Periodicals, Inc.