Thermo-optical properties of poly(dimethylsiloxane)/liquid crystal and poly(methylphenylsiloxane)/liquid crystal blends are investigated. Two low molecular weight liquid crystals are considered: 4-cyano-4'-n-pentyl-biphenyl or 5CB and the eutectic mixture of cyanoparaphenylene derivatives known as E7. Equilibrium phase diagrams are established by polarized optical microscopy and analyzed within mean field theories of isotropic mixing and nematic order. Effects of the methyl-phenyl substitution, the nature of liquid crystal and the polymer molecular weight on the phase diagram are discussed.