Thermodynamic Properties of Toluene Solutions of Low Molecular Weight Polystyrenes over Wide Ranges of Concentration

Second and third virial coefficients, A 2 and A 3, as well as the reciprocal of the osmotic compressibility ∂ Π /∂ c up to high concentrations were measured for low molecular weight polystyrenes dissolved in a good solvent toluene, by sedimentation equilibrium. The results were compared with a theory based on the single-contact approximation, where the polymer chain is viewed as a spherocylinder bearing hard-core and square-well potentials, to determine the hard-core diameter and the depth of the square-well potential of polystyrene in toluene. Furthermore, the present results of A 2, A 3, and ∂ Π /∂ c were combined with previous ones for higher molecular weight polystyrenes in toluene to examine application limits of the single-contact approximation. It was found that ∂ Π /∂ c for a polymer concentration higher than ca. 0.1 g/cm 3 is described by the theory of the single-contact approximation, irrespective of the polystyrene molecular weight, indicating that the effect of multiple contacts on ∂ Π /∂ c is screening off in the concentrated region.