The objective of this work is to develop a thermodynamic study of poly-vinyl acetate (PVAc) – methanol (MET), polyethylene (PE) – cyclohexane (CX) and polyethylene – p-xylene (p-XYL) mixtures by means of Intrinsic Viscosity (IV) technique, with the aim of obtaining the Flory Huggins polymer-solvent interaction parameter. As it can be seen, the higher is the value of viscous-average molecular weight of the polymeric materials (Mw), the higher is the IV. From the Intrinsic Viscosity data, the Flory-Huggins parameters of the studied couples were calculated following the Stockmayer-Fixman procedure. The obtained parameter, at 60°C, of both PE – CX and PVAc – MET pairs is lower than 0.5 which, according to Flory Huggins theory, implies that, at polymer infinite dilution, the polymer and the solvent are completely compatible. However, the Flory Huggins parameter PE – p-XYL couple is higher than 0.5 so this couple is not completely compatible.