Thermoreversible Cylinder−Sphere Transition of Polystyrene-block-polyisoprene Diblock Copolymers in Dioctyl Phthalate Solutions
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We present experimental results of a thermoreversible morphological transition between spheres and cylinders for polystyrene-block-polyisoprene diblock copolymers (SI) in dioctyl phthalate solutions. Morphologies were characterized using small-angle X-ray scattering (SAXS), and spherical and cylindrical states were found above and below the order−order transition (OOT) temperature, TOOT, respectively. TOOT increased with an increase of polymer concentration for the range covered in this study (higher than 70 wt % polymer concentration). The concentration dependence of TOOT was found to be given by the relationship of (χeffrC)OOT/φprC = A + B/TOOT, where (χeffrC)OOT denotes the critical value of the product of χeff and rC at the cylinder−sphere OOT, χeff is the effective interaction parameter between styrene and isoprene segments in the presence of solvent, rC is the reduced degree of polymerization of an entire block copolymer, and φp is the volume fraction of the block copolymer in the solution. A and B ...