High-Pressure Dynamic Light Scattering of Poly(ethylene-<i>co</i>-1-butene) in Ethane, Propane, Butane, and Pentane at 130 °C and Kilobar Pressures

Abstract

Poly(ethylene- co -1-butene) diffusion in ethane, propane, butane, and pentane indicates that ethane solutions are remarkably different. For propane, butane, and pentane the dynamic second virial coefficient, k D, is negative near the phase boundary, increases rapidly to positive values within ∼100 to 200 bar of the respective phase boundary, and approaches a constant value at high pressures. For ethane, k D is also negative near the phase boundary; it increases at a slower rate and becomes only slightly greater than zero. k D for all four solvents superpose when plotted against “methyl” molar density, suggesting thermodynamic interactions rather than hydrodynamic forces dominate. For propane, butane, and pentane the hydrodynamic radius, R H, also starts at a low value near the phase boundary and increases to the same value for all three alkanes. For ethane R H is ∼30% smaller than those for the higher alkanes, reflecting the poor quality of ethane even 1000 bar above the phase boundary.