Thermal analysis of styrene–alkyl methacrylate polymers. I. Glass transition temperatures

The glass transition temperatures ( T g 's) of several polystyrenes and styrene–alkyl methacrylate copolymers and terpolymers were measured using thermomechanical analysis (TMA) and differential scanning calorimetry (DSC). The polymers studied had number‐average molecular weights from 3000 to 250,000 g/mole. The results indicate that the composition dependence of the T g 's for the copolymers and terpolymers can be satisfactorily described by a general Fox equation. In general, the measured T g 's of the copolymer and terpolymer samples depend more on the steric effects of the constituent pendent groups than on their molecular weights. The chain flexibility rather than the size of the pendent group is the determining factor in the glass transition properties of the styrene polymers.