Glass Transition Temperature of Polya-α-methylstyrene by Differential Scanning Calorimetry

Glass transition temperature (Tg) studies on poly-α-methylstyrene having M n values ranging from 2.9 × 103 to 7.0 × 104 were carried out with the DSC-2 differential scangng calorimeter. The variation of Tge (at q = l°K/min) with M n obeys the relation, Tge (°K) = 453–3.1 × 105 M n. The enthalpy change ΔH observed near the glass transition temperature drops to zero for zero annealing time and zero extrapolated heating rate conditions, suggesting that it is not necessary to postulate a first order transition to account for energy absorption. Operating with longer annealing periods or low heating rates yields similar trends as far as the AH values are concerned. Tg extrapolated to zero ΔH for zero extrapolated heat-ing rate conditions was found to increase with increasing annealing time.