Thermodynamic Studies on the Glass Transition and the Glassy State of Polymers. III. Poly(α-methylstyrene)

Abstract

For two series of glasses of poly(α-methylstyrene), the densified glasses formed under various high pressures at the ordinary cooling rates(1°C/min) and slowly cooled glasses formed at various slow rates of cooling under atmospheric pressure, heats of solution, and specific heats were measured. In the glass-forming processes, dilato-metric measurements were also made. The results differ in many points from those of polystyrene reported in previous papers. For example, the glass transition temperature Tg, the specific volume Vs at 30°C, and heat of solution or the enthalpy H of the densified glass do not vary linearly with the glass-forming pressure P. Consequently (∂Tg/∂P) and (∂H/∂P) decrease and β′=−(∂lnVs/∂P) increase with increase of pressure. However, the theoretical relations about (∂Tg/∂P) derived by Nose are shown to be valid in these cases too, at least below the pressure of 450 kg/cm2. The criterion of the iso-configurational entropy or energy for Tg is established only under near atmospheric pressure. For the slowly cooled glasses, the relations ΔH=ΔCpΔTg and ΔV=VΔαΔTg are derived and confirmed. The small value of ΔCpintra calculated is discussed in comparison with the value for polystyrene, where ΔCpintra is the specific heat change at Tg associated with intramolecular degrees of freedom.