Determination of the Flory-Huggins interaction parameter of polystyrene-polybutadiene blends by thermal analysis

Blends of polystyrene (PS) and polybutadiene (PBD) were investigated by differential scanning calorimetry. From the phase composition diagram of the blends, it appears that PBD dissolves more in the PS-rich phase than does PS in the PBD-rich phase. This result is consistent with the behavior of the specific heat increment at the glass transition temperature of PBD in the PS-PBD blends. From the measured glass transition temperature and apparent weight fractions of PS and PBD dissolved in each phase, values of the Flory-Huggins polymer-polymer interaction parameter (X₁₂) were determined to be 0.0040-0.0102 depending on the composition and molecular weights of the PS and the PBD. No significant difference in X₁₂ was observed among the blending methods. The composition-dependent value of the Flory-Huggins polymer-polymer interaction parameter was found to be similar to the value of X₁₂. The polymer-polymer interaction parameter appears to depend on the degree of polymerization of the polymers as well as on the apparent volume fraction of the polymers dissolved in each phase.