Phase separation in polymer solutions: II. Determination of thermodynamic parameters of poly (2,6-dimethyl-1,4-phenylene oxide) toluene mixtures

In liquid systems where it is possible to perform light scattering experiments at the melting points of polymer solutions without nucleation taking place because of undercooling, the thermodynamic parameters necessary to calculate the correction parameter g in the Flory-Huggins equation as modified by Koningsveld can be determined. In the system poly(2,6-dimethyl 1,4-phenylene oxide)-toluene crystallization will be induced by liquid-liquid phase separation at temperatures below the melting points. The Huggins interaction parameter x, calculated from light scattering data, shows negative values for solutions up to 24.5 weight per cent of polymer. This indicates specific interactions between polymer and solvent molecules. A combination of data from light scattering and from calculations based on the theory of melting point depression affords the values necessary for calculating the free enthalpy of mixing ΔG