Thermodynamics of PMMA/SAN blends: Application of the Sanchez-Lacombe lattice fluid theory

Polymer blends of poly(methyl methacrylate) (PMMA) and poly(styrene-co-acry lonitrile) (SAN) with an acrylonitrile content of about 30 wt % were prepar ed by means of solution-casting and characterized by virtue of pressure-vol ume-temperature (PVT) dilatometry. The Sanchez-Lacombe (SL) lattice fluid t heory was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalpy of the mixing, the volume change o f the mixing, and the combinatorial and vacancy entropies of the mixing for the PMMA/SAN system. A new volume-combining rule was used to evaluate the close-packed volume per mer, upsilon*, of the PMMA/SAN blends. The calculat ed results showed that the new and the original volume-combining rules had a slight influence on the FH interaction parameter, the enthalpy of the mix ing, and the combinatorial entropy of the mixing. Moreover, the spinodals a nd the binodals calculated with the SL theory by means of the new volume-co mbining rule could coincide with the measured data for the PMMA/SAN system with a lower critical solution temperature, whereas those obtained by means of the original one could not.