Solubility of Poly (phenylene ether) to Polystyrene-<i>block</i>-polyethylenebutylene-<i>block</i>-polystyrene Triblock Copolymers

Polystyrene-block-polyethylenebutylene-block-polystyrene (SEBS) triblock copolymers are widely utilized as thermoplastic elastomers. In this study, solubilization of poly (phenylene ether) (PPE) into polystyrene (PS) microdomains was examined in order to improve the heat resistance of the SEBS triblock copolymers, where the PPE homopolymer has a higher glass transition temperature than PS and is generally known to be totally miscible with PS homopolymers with any composition. An ordinary solvent-cast method was employed for the sample preparation. As a result, macroscopic phase separation took place, although a small quantity of PPE was blended. The macroscopically phase-separated structures and microphase-separated structures were analyzed by the small-angle X-ray scattering technique and complementarily by the transmission electron microscopic observation. An appreciably broad interface between the macroscopically phase-separated domains was observed in SEBS/PPE solvent-cast samples. Based on the assumption that the cast solvent is more or less accumulated in the interface, the mechanism of forming such a broad interface is presented.