In this work, both the implicit penultimate model and a version of the terminal bootstrap model were fitted to extensive k̄p data covering a temperature range of 17.9-57.2 °C, for the copolymerization of styrene and methyl methacrylate (STY-MMA). The average activation energies and frequency factors were also calculated for STY-MMA copolymerizations, and the physical meaning of these parameters was explored. Insufficient composition data at the temperatures studied, together with the extreme sensitivity of the fitted model parameters to small errors in the kinetic data and the fixed constants, precluded the attachment of any physical significance to the parameters obtained. Nevertheless, two important conclusions can be drawn from this work. Firstly, there appears to be a temperature effect on the average radical reactivity ratios (s = s1 = s2), which suggests that there may be an enthalpic component to any penultimate unit effect present. Secondly, it appears that the bootstrap model is not a realistic alternative to the implicit penultimate model for describing the kinetics of ordinary copolymerizations such as STY-MMA.