SYNOPSISViscosity and density of homogeneous one-phase solutions (1 wt %) of polyethylenes with narrow molecular weight distributions ( M , = 2150, 15,520, 108,000, and 420,000) in npentane were determined at 398,413, and 428 K over a pressure range from 20 to 60 MPa. Measurements were done with a special falling cylinder type viscometer that permits simultaneous determination of viscosity, density, and phase state of the solutions. It is shown that the viscosities of these solutions can be correlated with density ( p ) using the exponential relationships p = A exp {B/(1 -V,p)} or p = C1 exp (C,p), which are based on free-volume considerations. Analysis of the temperature dependence of viscosity at fixed pressures, and its pressure dependence a t fixed temperatures show that the flow-activation energies for these solutions are in the range 8-12 kJ/mol, and the apparent activation volumes are in the range 30-45 cm3/mol. Evaluation of the specific viscosity and analysis of the molecular weight dependence of intrinsic viscosity in accordance with Mark-Houwink type relationship p = KM" suggest a value of 0.5 for the exponent a, which is typical of poor or theta solvents.

Volumetric properties of binary mixtures of carbon dioxide and sulfur hexafluoride have been determined using a specially designed high-pressure variable-volume view cell. The data are reported for mixtures containing 0, 9, 20.2, 31, 35.6, 50, and 100% by mass sulfur hexafluoride over a temperature range from 296 to 430 K at pressures up to 70 MPa. At these conditions, depending upon the mixture composition, densities are observed to vary in the range from 0.7 to 1.6 g/cm3.