A precise data set describing the kinetics of the free radical copolymn. of acrylamide/acrylic acid (AM/AA) in the range of low total monomer concn. as a function of the pH, total monomer concn., initiator concn., and comonomer ratio is presented. Strong impact on the reactivity ratios has been identified for the pH and total monomer concn. Specifically, at const. total monomer concn. of 0.4 mol/l and T=313 DegK the reactivity ratio of AM increases from 0.54 at pH 1.8 to 3.04 at pH 12. Contrarily, the reactivity ratio of AA decreases from 1.48 to 0.32. The crossover occurs at pH ~ 4.2. Electrostatic effects due to the variation of the degree of ionization of AA are primarily suggested to influence the kinetics. When the total monomer concn. increases from 0.2 to 0.6 mol/l at const. pH=12, the reactivity ratios of AM and AA decrease from 4.01 to 2.13 and increase from 0.25 to 0.47, resp. Redn. of electrostatic repulsion between the ionized monomer AA and partially charged growing polymer chain ends due to higher ionic strength at higher total monomer concn. serves as explanation of the effect. The precise data set is the prerequisite for a novel approach to calc. copolymer compns. in case of variable monomer reactivity. [on SciFinder (R)]