The copolymerization of methyl methacrylate and acrylonitrile has been studied in the bulk phase. Experiments for estimating reactivity ratios were conducted at 60, 100, 120, and 140 degrees C. Tidwell-Mortimer and the feed composition constraint approaches were used to design the experiments. The error in variables model (EVM) method was employed to evaluate the reactivity ratios and analyze the error involved. The results show that the reactivity ratios do not vary significantly with temperature up to 140 degrees C. (c) 2006 Wiley Periodicals, Inc.