Predicted miscibility of polystyrene and poly(α-methyl styrene) and comparison with experiment

The free energy of mixing of polystyrene with poly(α-methyl styrene) has been calculated using the Flory-Huggins expression and the more recent Flory theory which takes account of free volume effects. The double tangents to the free energy-composition curves were used to define phase separation points and hence the expected phase diagram for the system. Both approaches reproduce the observed behaviour reasonably well but in the latter case this is true only if a semi-empirical entropy parameter is included. The interaction of the polymers with the solvents used to prepare the blends is discussed.