E. Kiran et Z. Gokmenoglu, HIGH-PRESSURE VISCOSITY AND DENSITY OF POLYETHYLENE SOLUTIONS IN N-PENTANE, Journal of applied polymer science, 58(12), 1995, pp. 2307-2324
Viscosity and density of homogeneous one-phase solutions (1 wt %) of p
olyethylenes with narrow molecular weight distributions (M(w) = 2150,
15,520, 108,000, and 420,000) in n-pentane 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 sim
ultaneous determination of viscosity, density, and phase state of the
solutions. It is shown that the viscosities of these solutions can be
correlated with density (rho) using the exponential relationships mu =
A exp {B/(1 - V-o rho)} or mu = C-1 exp (C-2 rho), which are based on
free-volume considerations. Analysis of the temperature dependence of
viscosity at fixed pressures, and its pressure dependence at fixed te
mperatures 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 cm(3)/mol. Evaluation of the specific viscosity and
analysis of the molecular weight dependence of intrinsic viscosity in
accordance with Mark-Houwink type relationship mu = KM(a) suggest a v
alue of 0.5 for the exponent a, which is typical of poor or theta solv
ents. (C) 1995 John Wiley & Sons, Inc.