Experimental data for the copolymerization of methyl methacrylate (MMA) and alpha-methyl styrene (alpha-MS) were collected at 100 and 120degreesC. Measurements of conversion, polymer composition and number- and weight-average molecular weights were taken up to high conversions. The data were coupled with data from Palmer et al. and compared to model predictions from a process simulator. The simulator was developed using the Java((TM)) programming language and incorporated the effects of depropagation for both monomers. Prediction of polymer composition was reasonable, whereas some discrepancies occurred between the data and predictions of conversion and molecular weight at certain reaction conditions. At conditions of high MMA feed content, higher molecular weights resulted in diffusion-controlled polymerization kinetics. At higher alpha-MS levels and/or at the highest temperature level, stronger depropagation effects and thus, lower polymer molecular weights and lesser diffusion effects on the polymerization kinetics resulted.