EVALUATION OF EQUATION-OF-STATE PARAMETERS FROM PVT DATA

The characteristic parameters for three different equation-of-state (E OS) theories have been determined for polystyrene and low-molecular we ight polyisoprene using pressure-volume-temperature (PVT) data. Basica lly two procedures for the calculation of characteristic parameters we re applied. The characteristic parameters were calculated, firstly, fr om coefficients of expansion, compressibilities and densities, and sec ondly, by fitting the corresponding EOS to PVT data minimizing the sum of the squares of the differences between experimental and calculated pressures. The characteristic parameters obtained by the two methods are compared with regard to their ability to describe PVT data. A comp arison of the three different EOS theories reveals that, for describin g polymeric liquids, the modified cell model of Dee and Walsh is super ior to the theory of Flory, Orwoll and Vrij as well as to the lattice fluid theory of Sanchez and Lacombe. Finally, formulae are given to co nvert the characteristic parameters from one theory into those of anot her.