Effects of pressure and molecular weight on the miscibility of polystyreneand cyclohexane

With the aid of Sanchez-Lacombe lattice fluid theory (SLLFT), the phase dia grams were calculated for the system cyclohexane (CH)/polystyrene (PS) with different molecular weights at different pressures. The experimental data is in reasonable agreement with SLLFT calculations. The total Gibbs interac tion energy, g*(12) for different molecular weights PS at different pressur es was expressed, by means of a universal relationship, as g(12)* =f(12)* (P - P-0) nu*(12) demixing curves were then calculated at fixed (near crit ical) compositions of CH and PS systems for different molecular weights. Th e pressures of optimum miscibility obtained from the Gibbs interaction ener gy are close to those measured by Wolf and coworkers. Furthermore, a reason able explanation was given for the earlier observation of Saeki et al., i.e ., the phase separation temperatures of the present system increase with th e increase of pressure for the low molecular weight of the polymer whereas they decrease for the higher molecular weight polymers. The effects of mole cular weight, pressure, temperature and composition on the Flory Huggins in teraction parameter can be described by a general equation resulting from f itting the interaction parameters by means of Sanchez-Lacombe lattice fluid theory.