The copolymerization behavior of 3-methyl-2-vinylthiophene with methyl methacrylate or ethyl acrylate in bulk, using free radical initiation was investigated. The copolymerizations were performed according to the experimental design scheme of Mortimer and Tidwell (1). The experimental results were analyzed by using a nonlinear least squares error-in-variables method. In both cases the 3-methyl-2-vinylthiophene proved to be the more reactive monomer.