HIGH-PRESSURE, MOLECULAR WEIGHT-DEPENDENT BEHAVIOR OF (CO)POLYMER-SOLVENT MIXTURES - EXPERIMENTS AND MODELING

Cloud-point data as a function of polymer molecular weight are presented for polyethylene (PE)-dimethyl ether (DME) and poly(ethylene-co-methyl acrylate) (35 mol % acrylate) (EMA)-butane mixtures to temperatures of 210-degrees-C and pressures of 2700 bar. The cloud-point curves for PE-DME, at temperatures below approximately 125-degrees-C, and EMA-butane, at temperatures below approximately 150-degrees-C, order with respect to the weight average molecular weight. The cloud-point behaviors for these two systems along with the poly-(ethylene-co-acrylic acid) (4.1 mol % acid) (EAA)-butene system are modeled with the statistical associating fluid theory (SAFT). For each system, a constant value of the binary interaction parameter, k(ij), is fit to the parent-solvent cloud-point curve and is used in subsequent calculations. For the EAA system, values for the pure component energy of acid dimerization and the volume of association are obtained from literature spectroscopic data. The SAFT equation, with k(ij) = 0.0405, can only predict the correct qualitative trends observed for the effect of molecular weight on the PE-DME system probably because SAFT does not account for polar DME-DME interactions. A quantitative fit of the EMA-butane system is obtained with k(ij) = 0.026 and a slightly adjusted value of the nonspecific interaction energy for EMA. The calculations for the EAA-butene system with k(ij) = -0.020 are in good agreement with experimental data.