Acrylonitrile (M1) was copolymerized with haloalkyl acrylates/ methacrylates (M2) in a water-acetone [2:1 (v/v)] medium at 40°C. The composition of the copolymers was determined from the nitrogen content, and the reactivity ratios were calculated by the Kelen-Tüdos method. The low ri values (acryionitrile) in acrylonitrile (AN)-2-bromoethyl acrylate (BEA)/2-bromoethyl methacrylate (BEMA) as compared to acrylonitrile-2-chloroethyl acrylate (AN-CEA) and acrylonitrile-2-chloroethyl methacrylate (AN-CEMA) may be attributed to the higher reactivity of bromo-alkyl monomers (BEA and BEMA) toward the polyacrylonitrile radical. Further, r1tends to decrease when M2is changed from acrylate to methacrylate, viz., r1(AN-BEA)> r1(AN-BEMA), while the trend is reversed in chloroalkyl acrylate monomers, i.e., r1(AN-CEA) < r1(AN-CEMA).