Retrograde melting behavior in polyolefin + solvent + antisolvent solutions



The SAFT1 equation of state captures the melting retrograde behavior for a ternary system of poly(ethylene-co-octene-1) + isooctane + ethylene. The melting temperature minimum depends on the polymer branch density, solvent composition, polymer concentration, and polymer molecular weight, in decreasing order of sensitivity. Furthermore, the effects of the solvent/antisolvent ratio and polymer concentration on the melting temperature are nonmonotonic, that is, their sign may change in going from low to high pressures. Finally, the sign of the slope of the melting curve depends only on the difference between the partial molar volume of polymer in solution and the molar volume of pure solid polymer.