Cloud point measurements and calorimetric properties were considered for binary systems of polystyrene/4cyano-4'-n-octylbiphenyl (8CB), and deuterated polystyrene/8CB. The experimental phase diagrams were established using polarizing optical microscopy and differential scanning calorimetry. The experiments were realized in the range of temperatures from 25 to 75 degrees C, in which the 8CB presents a smectic A structure, a nematic and an isotropic phase. The phase behavior of both systems were analyzed using a combination of the Flory-Huggins lattice model for isotropic mixing and the Maier-Saupe-McMillan theories for anisotropic ordering. A good agreement was obtained between theoretical considerations and experimental data.