Copolymers of sodium o-methacryloylaminophenylarsonate (o-MAPHA-Na) 1 and p-methacrylolylaminophenylarsonate (p-MAPHA-Na) 2 with sodium acrylate (AA-Na) 3, sodium methacrylate (AM-Na) 4 and acrylamide (AAD) 5 were prepared by free radical polymerization in aqueous media at 70 degrees C using potassium persulfate (K2S2O8) as the initiator. The total monomer concentration was carried out at 0.5M and the feed ratio (M-1 : M-2) was varied from 10 : 90 to 90 : 10 mol%. The kinetic study was carried out by dilatometric method. The copolymer compositions were calculated by arsenic content in the copolymers. The As content (ppm) was determined by atomic absorption spectrometry (AAS). The reactivity ratios (r(1), r(2)) were estimated by the Kelen-Tudos linearization method as well as error-in-variables method using the computer program RREVM (R). In all cases, r(1) < 1 and r(2) > 1, indicating a tendency to form random copolymers. The values suggest that the copolymers contain a larger proportion of comonomer (i.e., AA-Na, AM-Na, or AAD). Weight-average molar masses ((M) over bar (w)) of copolymers were determined by multi-angle light scattering. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 2849-2858, 2010