Specific volume of polysulfone as a function of temperature and pressure

The pressure–volume–temperature (PVT) properties of a commercial polysulfone derived from bisphenol A and 4,4′‐dichlorodiphenylsulfone are studied experimentally and theoretically in the temperature range 30–370°C and for pressures to 2000 kg/cm 2 . PVT surfaces are determined for an annealed glass, formed under zero pressure, and for the melt. Two glass‐transition lines must be distinguished: T (P) which is the intersection of the glass and melt PVT surfaces, and T g (P), which is obtained by pressurizing the melt isothermally. The application of Ehrenfest‐type equations to these transitions are discussed. The Prigogine–Defay ratio r = Δ k Δ C p / T V (Δα) 2 at P = 0 is found to be equal to 0.95 (±20%), using Δ C p data determined on identical samples. The melt data is compared with the Simha–Somcynski hole theory, using the reducing parameters V * = 0.788 cm 3 /g, T * = 12,560°K, P * = 10,875 bar. The hole fraction appearing in the theory is found to be constant along T (P), but the glass PVT relationship cannot be reproduced by using the Simha–Somcynsky theory together with the assumption that the hole fraction remains constant in the glass. At P = 0 the hole fraction must be allowed to decrease with decreasing temperature, but at a slower rate than in the melt.