CALCULATING POLY(ETHYLENE-CO-ACRYLIC ACID)-SOLVENT PHASE-BEHAVIOR WITH THE SAFT EQUATION OF STATE

Statistical Associating Fluid Theory (SAFT) is used to model the cloud -point behavior of poly(ethylene-co-acrylic acid), with up to 7 mol % acid content, in propane, butane, propylene, butene, and dimethyl ethe r at temperatures to 250 degrees C and pressure to 2600 bar. The value s for the pure component temperature-independent segment volumes, nons pecific interaction energies, and the numbers of segments per molecule are equal to those used for polyethylene, because these copolymers co ntain modest amounts of acrylic acid repeat units. Two different appro aches are used to determine values of the pure component energy of hyd rogen bonding, epsilon/k, and the binary interaction parameter, k(ij). In one approach, epsilon/k for acid dimerization is obtained from lit erature spectroscopic data and a constant value of hii is fit to each copolymer-solvent cloud-point curve. Increasing the value of k(ij) shi fts the predicted cloud-point curves to higher temperatures and pressu res. For the five solvents used in this study, k(ij) decreased steadil y in the range of 0.040 to -0.025 as the acid content in the copolymer increased. The predicted cloud-point curves are in good agreement wit h experimental data, and the impact of hydrogen bonding on the phase b ehavior is well represented, even if hii is set equal to zero. For the second approach, epsilon/k is set to similar to 90% of the value obta ined from spectroscopic data as determined from a fit of a single poly (ethylene-co-acrylic acid)-butane cloud-point curve, while k(ij) is fi t to the corresponding polyethylene-solvent system. This approach requ ires less mixture data than the previous approach, and the calculated cloud-point curves are also in good agreement with experimental data, except for the EAA-DME systems. (C) 1995 John Wiley & Sons, Inc.