PHASE-BEHAVIOR OF EVAL POLYMERS IN WATER-2-PROPANOL COSOLVENT

Isothermal phase diagrams for semicrystalline poly(ethylene-co-vinyl a lcohol) (EVAL) using two nonsolvents (water and X-propanol) serving as a cosolvent system have been determined. The locations of the liquid-l iquid demixing and the crystallization-induced gelation in the phase d iagrams at 60 degrees C were identified. Attempts were made to correla te the experimental findings with predictions on the basis of the modi fied Flory-Huggins theory for ternary ablutions using three binary int eraction parameters (chi(ij)) and one ternary interaction parameter (c hi(T)). No good agreement was found between the theoretical prediction s and experimentally obtained data if the ternary interaction paramete r was neglected. But an improvement can be obtained when a ternary int eraction parameter is considered. The optimum value has been found to be approximately -1.7 + 0.5(phi 2) + 1.0(phi 3). Therefore, it is nece ssary to introduce the ternary interaction parameter when the binary p arameters provide an inadequate description of phase behavior, but in most systems studied so far the-ternary interaction parameter is ignor ed.