MISCIBILITY OF POLY(ETHYLENE OXIDE) POLY(ETHYLENE-CO-VINYL ACETATE) BLENDS - SIMULATION OF PHASE-DIAGRAM

Blends of poly(ethylene oxide)/poly(ethylene-co-vinyl acetate) (PEO/EVAc-1) have been prepared by casting from a common solvent. The miscibility of the mixture is studied by using differential scanning calorimetry (d.s.c.) and dilatometry. The blends, as obtained, show a single, composition-dependent, glass transition that fits the Fox equation well, indicating the presence of a homogeneous amorphous phase. Some blends phase-separate on heating. The cloud-point curve of the system is drawn by detecting on the d.s.c. thermograms one or two glass transition temperatures depending on whether or not phase separation takes place at a fixed annealing temperature. The cloud-point curve is very skew, with a maximum at around 80 wt% PEO content and t = 210 +/- 10-degrees-C. The theoretical approach of group contributions and solubility parameters predicts no miscibility for the system under investigation, whereas a lower critical solution temperature is predicted by Flory's equation-of-state theory. Using values of X12 interactional parameter, derived from the experimental thermal expansion coefficients of the blends, a simulated spinodal phase boundary is obtained.