Intrinsic Viscosity of Polystyrene in Toluene-Supercritical Carbon Dioxide Mixtures

Abstract

Intrinsic viscosities [η] were determined for five polystyrene samples ranging in molecular weight M_w from 9.0 × 10⁴ to 1.2 × 10⁶ in toluene-supercritical carbon dioxide mixtures with different weight fractions of CO₂ (denoted as w(CO₂ )) at 40 °C in a pressure range P = 7.0-10.0 MPa using a rolling-ball viscometer. For every sample [η] was a gradually increasing function of P, indicating that the polystyrene coil expands with increasing P. At fixed P and w(CO₂ ), the molecular weight dependence of [η] was expressed in the form [η] α M_w^a . The exponent a remarkably changed with w(CO₂ ) at constant P; for example, it decreased from 0.68 (a good solvent value) to 0.42 (a poor solvent value below the theta point where a = 0:5) with an increase in w(CO₂ ) from 15 to 31% at P = 7.0 MPa. The solvent goodness was quantified in terms of the binarycluster integral determined by analyzing the [η] data according to the two-parameter theory.