Pressure-volume-temperature of molten and glassy polymers

摘要

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 Y'*. 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 (FFP=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, 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*. (c) 2006 Wiley Periodicals, Inc.