Determination of the thermodynamic polymer‐polymer interaction parameter of miscible blends prepared from two crystalline polymers

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Abstract
The melting points of miscible blends prepared from two crystalline polymers, poly(caprolactone) (PCL), and Saran a random copolymer of vinylidene chloride with vinyl chloride [P(VCl2‐VC)], vinyl acetate [P(VCl2‐VA)], or acrylonitrile [P(VCl2‐AN)], have been measured by differential scanning calorimetry as a function of the crystallization temperature. The equilibrium melting points of these blends have been determined by Hoffman‐Weeks plots. From two series of data, one of which was obtained by measuring the melting points of PCL crystals and the other by measuring the melting points of Saran crystals, the thermodynamic polymer‐polymer interaction parameters of PCL/Saran blends have been calculated over the full range of composition. The two series of data merge into a smooth curve, which is composition dependent, despite the fact that the melting points of PCL and P(VCl2‐VC) or P(VCl2‐VA) are very different at 58.1, 183.5, and 184.2°C, respectively. Calculations using the “equation of state” Prigogine‐Flory thermodynamic theory indicate that the temperature dependence of the thermodynamic interaction parameter in typical polymer blends is small, which agrees with the experimental results.