| Abstract
| - Phase transitions in sphere-forming polystyrene-block-polyisoprene-block-polystyrene (SIStriblock) copolymer and its blends with polystyrene (PS) were investigated using oscillatory shearrheometry, 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. Itis 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 thermalequilibrium 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) of Vector 4113 is found to be ca. 205 °C, and the DMT temperature (TDMT) is much higher than220 °C, the highest experimental temperature employed to avoid thermal degradation/cross-linkingreactions. The addition of various amounts of low-molecular-weight PS enabled us to estimate, viaextrapolation, the TDMT of Vector 4113 to be ca. 260 °C. On the other hand, SIS-100 is found to haveTLDOT of 85 °C and TDMT of 105 °C. Transmission electron microscopy confirmed the existence of disorderedmicelles in both Vector 4113 and SIS-100 between TLDOT and TDMT. Phase diagrams for (SIS-100)/PSblends were constructed using TLDOT, TDMT, and cloud point measurements.
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