An anal. approach to predict copolymer compns. is presented for the particular case that the reactivity of one monomer (B) alters under the influence of one measurable medium parameter. Terpolymn. math. treatment was applied to binary systems (A/B), which turn into ternary systems (M1, M2, M3) in a defined range between two extremes of the medium parameter. The approach needs as input data a relationship describing the coexistence of two derivs. (M2, M3) of B as a function of the influencing parameter, knowledge of homopolymn. kinetic data of B, and reactivity ratios, rA and rB, only at the extremes of the variable medium parameter. As a case study, the copolymn. of acrylamide/acrylic acid mixts. in aq. medium was selected with the pH as variable parameter. Good agreement of predicted and exptl. data was proved. The approach provides a useful tool to significantly decrease the no. of polymn. expts. needed to identify the effect of medium parameters on the polymn. kinetics. The principle of the approach is proposed to treat any set of two monomers if one alters the characteristics under the influence of any measurable medium parameter. [on SciFinder (R)]