Equation of State for Polystyrene

Abstract

Practical considerations emphasize the desirability of formulating an adequate equation of state for polystyrene. A fairly satisfactory one is this simplified version of van der Waals' equation, (P+π)(V−ω)=nRT,where π is the internal pressure (or cohesive energy density) and ω is the volume at absolute zero, by extrapolation. Evaluating constants from thermal expansion data and expressing P in p.s.i., V in cc per gram, and T in degrees Kelvin, this becomes (P+27,000)(V−0.822)=11.6T.Agreement with compressibility measurements, which are described in some detail, is good. Discrepancies with room temperature values of sound velocity and cohesive energy density by swelling measurements are discussed briefly.