Abstract: | Poly(MMA‐ran‐St) samples were synthesized under monomer‐starved conditions (drop feeding method) by emulsion copolymerization. Their thermostability was determined by thermogravimetric analysis. The glass transition temperature (Tg) of the copolymers was determined by differential scanning calorimetry (DSC) and torsional braid analysis (TBA). The results showed that the MMA–St copolymers exhibit an asymmetric Tg versus composition curve, which could not be interpreted by Johnston's equation, taking the different contributions of the diads to the Tg of the copolymer into consideration. A new sequence distribution equation taking into account the different contributions of the triads was proposed to predict the copolymer Tg. The new equation fitted the experimental data exactly. The Tg determined by torsional braid analysis (TBA) is higher than the one determined by DSC, but the difference is not constant. The rheological behaviour of the copolymers was also studied and TgTBA‐TgDSC increased with the increasing flow index of the copolymer. © 2003 Society of Chemical Industry |