Vapor-Liquid equilibrium (VLE) of polymer + solvent mixtures is described by the chain-of-rotators (COR) equation of state (EOS) using segment parameters that are applicable to polymers of varying molecular weight. Segment parameters a and b are obtained from small molecules of the same chemical structure as the polymer segment. The segment parameter c is then obtained by fitting polymer pressure-volume-temperature (PVT) data. van der Waals and free energy matching mixing rules are investigated to describe mixtures of various types. Excellent correlation of VLE data is obtained for all mixtures studied by using only one constant interaction coefficient for a, k(12), in the van der Waals mixing rule independent of temperature or polymer molecular weight. VLE predictions from the COR EOS by using van der Waals mixing rules with zero k(12) as well as by using UNIFAC free energy matched mixing rules are presented. For the majority of systems studied, both predictive methods gave better or equal results compared to the UNIFAC-FV model (FV = free volume).