Nonaqueous solutions of polymers, especially polyethylene glycols and polypropylene glycols, are broadly used in various processes in lubricants, carriers, coupling agents, pharmaceuticals, and purification of bioactive compounds [1,2]. Vapor-liquid equilibrium (VLE) investigation in ternary solutions composed of two polymeric solutes and a nonaqueous solvent provides valuable information regarding predominant factors that control the phase behavior of these systems. An overview of the literature shows that although VLE data have been obtained for binary nonaqueous solutions of polymers [3,4], as far as we know, there is no study about ternary nonaqueous polymer-polymer solutions. In this work, the isopiestic technique has been used to study the VLE behavior of ternary systems composed of polymer 1 (polyethylene glycol) + polymer 2 (polyvinylpyrrolidone) + organic solvent (ethanol or 1-butanol). The effects of polymer structure and concentration on the slope of constant solvent activity lines and the magnitude of deviations from the semi-ideal behavior (Zdanovskii−Stokes−Robinson rule) [5] have been explained and related to the soluting-in or soluting-out effects occurring in the investigated systems.
