Pressure–volume–temperature of molten and glassy polymers

The pressure–volume–temperature ( PVT ) dependencies of several amorphous polymers (PS, PC, PPE, and PPE/PS 1:1 blend) in the glassy and molten state were studied. The Simha–Somcynsky ( S –S) lattice‐hole equation of state (EOS) was used. Fitting the PVT data in the molten state to the EOS yielded the free volume quantity, h = h ( T, P ), and the characteristic reducing parameters, P *, V *, and T *. The data within the glassy region were interpreted assuming that the latter parameters are valid in the molten and vitreous state, than calculating h = h ( T, P ) from the experimental values of V = V ( T, P ). Next, the frozen free volume fraction in the glass was computed as FF = FF ( P ). The FF values of polystyrene (PS) resins at ambient pressure showed little scattering ( FF P=1 = 0.691 ± 0.008), while their P‐ dependencies varied, reflecting the thermodynamic history of the glass formation as well as the PVT measurements protocol. The pressure gradient of T g was compared with the Ehrenfest relation for the second‐order transition; here also agreement depended on the method of vitrification. The experimental values of FF at ambient pressure decreased with increasing values of the characteristic temperature reducing parameter, T* .