Miscibility and immiscibility in functionalized associating polymer systems: polystyrene-poly(phenylene oxide) blends

The thermal properties of several families of polystyrene-poly(phenylene oxide), sulphonated polystyrene-poly(phenylene oxide), polystyrene-sulphonated poly(phenylene oxide), and sulphonated polystyrene-sulphonated poly(phenylene oxide) blends were studied by differential scanning calorimetry. The appearance of a single glass transition temperature, i.e. blend miscibility, depended on the level of sulphonation of one or both components of the blend. Even though blends formed from the unfunctionalized components were miscible over the complete composition range, miscibility was reduced as the sulphonation level increased in either component. A substantially broader range of miscibility was observed when both blend components were functionalized. Compared with blends containing one sulphonated component, where immiscibility could occur within a relatively modest sulphonation range (typically 2–4 mol%), blends with two sulphonated components retained miscibility over a substantially broader sulphonation range (typically 10 mol%). The results are interpreted in terms of the mean field theory involving interaction parameters for the individual monomer segments.