MODELING POLYETHYLENE SOLUTIONS IN NEAR AND SUPERCRITICAL FLUIDS USING THE SANCHEZ-LACOMBE MODEL

Effectiveness of the Sanchez-Lacombe model in predicting the high pressure phase behavior of solutions of polyethylene standards of molecular weights 2,150, 16,400, 108,000, and 420,000 in n-pentane and n-pentane-carbon dioxide binary solvents has been evaluated. It is shown that by proper adjustment of the characteristic temperature for the polymer, which is achieved by using data for one molecular weight sample, variations with respect to concentration and pressure are correctly predicted. The model correctly predicts also the solvent-dependent shift from LCST (Lower Critical Solution Temperature) to UCST (Upper Critical Solution Temperature) type behavior for these solutions upon increase in. the carbon dioxide content of the n-pentane-carbon dioxide binary solvent.