Phase behavior of ternary blends comprising poly(2,6-dimethyl phenylene oxide) and two styrene-based copolymers

The phase behavior of ternary blends consisting of poly(2,6-dimethyl phenylene oxide), PPO, and two styrene-comprising random copolymers with acrylonitrile, SAN, and maleic anhydride, SMA, was examined theoretically and by experiment. The three binaries, SAN/PPO, SMA/PPO, and SAN/SMA, are miscible in certain regions of copolymer compositions. It has been demonstrated that the corresponding miscibility region of the ternary system is less extended than the overlap region of the three binaries. Immiscibility of just one pair leads to an extended region of phase instability in the ternary system. More generally, phase separation in the ternary system is driven by dissimilarity of the binary interaction parameters. This may even cause phase instabilities in systems consisting of three miscible binaries. For selected immiscible systems, the fraction of material in interfacial regions was estimated. Results indicate that interfacial regions become more narrow with increasing distance from miscibility regions.