AbstractThe copolymerizations of acrylic (AA) and methacrylic (MAA) anhydrides (M1) with styrene (St) and methacrylonitrile (MAN) have been examined; similarly that of acrylic anhydride with allyl chloride. In these systems the reactivity ratio of an open unit radical (r1) is equal to that of a cyclized radical (r3), and the usual Alfrey‐Price equation is valid. By using a graphical method the ratios of the cross propagation rate constant to the cyclization rate constant (k12/kc) have been also evaluated. The following values for r1, r2, and k12/kc respectively have been found, M1 being the anhydride: for the system AA (M1)–St, 0.1, 0.17, and 4; for the system AA–MAN, 0.9, 0.04, and 0.14; for the system AA–allyl chloride, 11.5, 0.01, and 0. For the same systems with MAA, the values of r1, r2, and k12/kc were 0.26, 0.12, and 0.2 with St, and 1.6, 0.27, and about zero with MAN. These data indicate also that the cyclization reaction is always more pronounced for methacrylic anhydride than for the acrylic anhydride.