In this article, the thermodynamic behavior of polyvinylacetate (PVAc)-solvent, and polyethylene (PE)-solvent mixtures have been studied by determining the thermodynamic sorption parameters (enthalpy, entropy, and free energy), the mass-based solvent activity coefficients () and the Flory Huggins parameters (), by means of inverse gas chromatography (IGC) measurements. According to the Flory Huggins parameters of the PE-solvent mixtures, determined between 40 and 60 degrees C the compatibility (the ability to interact with each other) of this polymer with the different types of solvents follows this order: dispersion solvents>polar solvents>association solvents. In the case of PVAc mixtures, the thermodynamic parameters were determined between 60 and 80 degrees C, only for polar-type and association-type solvents due to, in the studied temperature range, the retention diagrams of dispersion solvents show that there are not bulk interactions. The Hildebrand solubility parameters of both polymers were also determined, according to Guillet procedure. The higher values of PVAc material (14.1 MPa0.5 for PE and 19.8 MPa0.5 for PVAc, at 60 degrees C) are related to the strong interactions of vinyl acetate monomer. POLYM. ENG. SCI., 56:36-43, 2016. (c) 2015 Society of Plastics Engineers