Phase Transitions in Sphere-Forming Polystyrene-block-polyisoprene-block-polystyrene Copolymer and Its Blends with Homopolymer

Abstract

Phase transitions in sphere-forming polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymer and its blends with polystyrene (PS) were investigated using oscillatory shear rheometry, transmission electron microscopy, and small-angle X-ray scattering (SAXS). For the investigation, a commercial grade of high-molecular-weight SIS triblock copolymer (Vector 4113, Dexco Polymers) and a low-molecular-weight SIS triblock copolymer (SIS-100) synthesized in our laboratory were used. It is found from oscillatory shear rheometry and SAXS that both Vector 4113 and SIS-100 undergo order−disorder transition (ODT) having a characteristic feature of lattice disordering/ordering transition (LDOT) of spheres, giving rise to a phase consisting of micelles with short-range liquidlike order at thermal equilibrium above ODT and demicellization/micellization transition (DMT), as a pseudo phase transition, giving rise to a micelle-free phase with only thermal composition fluctuations. The LDOT temperature (TLDOT...