Poly(methyl methacrylate-ran-styrene) copolymers were synthesized under monomer-starved conditions by emulsion copolymerization. The glass-transition temperatures (Tg's) of the copolymers were measured by differential scanning calorimetry (DSC) and torsional braid analysis (TBA). The results showed that the methyl methacrylate-styrene random copolymers produced an asymmetric T-g versus composition curve, which could not even be interpreted by the Johnston equation with different contributions of dyads to the T-g of the copolymer considered. A new sequence distribution equation concerning different contributions of triads was introduced to predict the copolymer's T-g. The new equation fit the experimental data exactly. Also, the T-g determined by TBA (T-gTBA) was higher than the one determined by DSC (T-gDSC) and the difference was not constant. The rheological behavior of the copolymers was also studied. T-gTBA - T-gDSC increased with increasing flow index of the melt of t e copolymer, and the reason was interpreted. (C) 2003 Wiley Periodicals, Inc.