Studies of poly(2,6‐dimethyl‐1,4‐phenylene oxide blends): I. Copolymers of styrene and maleic anhydride

Blends of poly(2,6‐dimethyl‐l,4‐phenylene oxide) and copolymers of styrene and maleic anhydride have been characterized by differential scanning calorimetry, dynamic mechanical analysis, and tensile measurements. Differential scanning calorimetry measurements indicate a single broadened glass transition for each blend of a 8 wt.% maleic anhydride copolymer, P(S‐8MA), but two glass transitions when the copolymer composition is 14 wt.% MA, P(S‐14MA). The glass transition temperatures of the former blends follow a sigmoidal dependence on blend composition, which is explained on the basis of evidence for phase separation from their dynamic mechanical tan 8 spectra. Tensile moduli of both blends reach a maximum at intermediate blend compositions; however, large‐strain mechanical properties are highly dependent on blend compatibility and the method of sample preparation. The more homogeneous P(S‐8MA) blends yield at low‐to‐intermediate copolymer compositions but fail in a brittle mode at higher compositions. All heterogeneous P(S‐14MA) blends undergo brittle failure, but comparison of experimetal values of ultimate stress and strain with predictions from empirical relationships developed for composites indicate that interfacial adhesion is strong in these systems.