Journal of Polymer Science Part B: Polymer Physics, Vol.33, No.4, 715-723, 1995
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 ether at temperatures to 250 degrees C and pressure to 2600 bar. The values for the pure component temperature-independent segment volumes, nonspecific interaction energies, and the numbers of segments per molecule are equal to those used for polyethylene, because these copolymers contain modest amounts of acrylic acid repeat units. Two different approaches are used to determine values of the pure component energy of hydrogen bonding, epsilon/k, and the binary interaction parameter, k(ij). In one approach, epsilon/k for acid dimerization is obtained from literature spectroscopic data and a constant value of hii is fit to each copolymer-solvent cloud-point curve. Increasing the value of k(ij) shifts the predicted cloud-point curves to higher temperatures and pressures. For the five solvents used in this study, k(ij) decreased steadily 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 with experimental data, and the impact of hydrogen bonding on the phase behavior 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 obtained from spectroscopic data as determined from a fit of a single poly(ethylene-co-acrylic acid)-butane cloud-point curve, while k(ij) is fit to the corresponding polyethylene-solvent system. This approach requires 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.