The melt miscibility of atactic poly(propylene) (a‐PP) with isotactic (i‐PP) and syndiotactic poly(propylene) (s‐PP), respectively, is investigated by diffusion experiments of i‐PP/a‐PP/i‐PP or s‐PP/a‐PP/s‐PP sandwich specimens using polarized light microscopy. It is shown that the system a‐PP/i‐PP is miscible in the melt, whereas for the system a‐PP/s‐PP no evidence for melt mixing is found. Pressure‐volume‐temperature (PVT) measurements of the three poly(propylene)s are carried out in order to determine the characteristic parameters of the Flory‐Orwoll‐Vrij equation‐of‐state theory. Theoretical predictions using the solubility parameter concept are in agreement with the observed miscibility behavior of the blends. Differences in the cohesive energy densities of a‐PP and i‐PP on the one side, and s‐PP on the other side, are found to be responsible for the phase behavior of the mixtures of poly(propylene)s with different stereoregularity. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1135–1144, 1997

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The characteristic parameters for three different equation-of-state (EOS) theories have been determined for polystyrene and low-molecular weight polyisoprene using pressure-volume-temperature (PVT) data. Basically two procedures for the calculation of characteristic parameters were applied. The characteristic parameters were calculated, firstly, from coeficients of expansion, compressibilities and densities, and secondly, 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 PVTdata.Acomparison ofthe three different EOS theories reveals that, for describing polymeric liquids, the modified cell model of Dee and Walsh is superior 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 convert the characteristic parameters from one theory into those of another.

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A comparison has been made between the Sanchez-Lacombe equation-of-state theory and the theory of Patterson for describing the phase behavior of various polymer blends. Phase diagrams have been determined as well as PVT data, in order to determine the reduction parameters of the polymers used. With these data the phase diagrams were simulated applying these two theories. Furthermore, the cause of compatibility or incompatibility, Le., the influence of free volume and enthalpic effects were investigated. Both theories show surprisingly similar behavior with respect to the mentioned properties.