Phase behavior of a water/2-propanol/poly(methyl methacrylate) cosolvent system

A phase diagram of poly(methyl methacrylate) in mixtures of water and 2-pro panol, individually nonsolvents for the polymer, was studied at 25 degrees C. For this system, there were two liquid-liquid demixing regions separated by a miscible region. This cosolvent phenomenon was thought to be a joint effect of the nonsolvents. The phase behavior was modeled according to modi fied Flory-Huggins chemical-potential equations, which accounted for the po ssible contribution from a ternary interaction in terms of a lumped paramet er, chi(123). The calculated phase-equilibrium curves (binodals) agreed wel l with the measured results. By contrast, if only binary interaction parame ters were considered, computations yielded binodals whose compositions depa rted significantly from the measured data. Using the wet phase inversion me thod with casting dopes selected on the basis of the phase diagram, are pre pared membranes with microporous structures in various coagulation baths, ( C) 2000 John Wiley & Sons, Inc.