In this article, bulk copolymerization of methyl methacrylate (MMA) with ethyl methacrylate (EMA) and n-butyl methacrylate (n-BMA) was carried out at 60 degrees C. The monomer reactivity ratios obtained by non-linear fitting with Mayo-Lewis equation were as follows: r(MMA) = 0.93 +/- 0.03, r(EMA) = 0.96 +/- 0.03 for the MMA/EMA, and r(MMA) = 0.99 +/- 0.05, r(n-BMA) = 1.11 +/- 0.06 for the MMA/n-BMA series. A new equation proposed in view of bond rotation flexibility (Liu et al., J Phys Chem B 2008, 112, 93), which contains mole fractions of triads and T-g's of corresponding periodic copolymers, was applied to describe the relation of T-g's of MMA-EMA, MMA-n-BMA copolymers with their compositions and sequence distribution. Excellent fitting results were obtained and T-g values of the assumed periodic copolymers were predicted by fitting the random copolymers. The influence of the substituent volume as well as substituent density on the T-g of poly(methyl methacrylate) (PMMA) was also tentatively predicted. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 3939-3944, 2009