The batch free-radical polymerization of nonionized methacrylic acid (MAA) in aqueous solution has been investigated at 50 degrees C and initial monomer concentrations Lip to 30 wt % MAA. The rate of conversion increases as the initial weight fraction of MAA decreases, a result explained by the dependence of the propagation rate coefficient, k(p), on monomer concentration. The conversion profiles measured at different MAA and initiator levels are represented by a polymerization model with con version-dependent k(p) taken from literature, and the termination rate coefficient, k(1), represented by a function including terms for segmental diffusion, translational diffusion, and reaction diffusion. The model includes chain transfer to monomer and is capable of representing polymer molecular weight averages and distributions, with the better fit obtained assuming that the transfer rate coefficient also varies with monomer concentration.