Macro- and Microphase Transitions in Binary Blends of Block Copolymers with Complementarily Asymmetric Compositions

Abstract

A unique phase transition between the state of “two macrophase-separated disordered phases” at higher temperatures and that of “a single phase with only a local order” at lower temperatures was observed in a binary mixture of polystyrene (PS)-block-polyisoprene (PI) copolymers by using small-angle X-ray scattering, light scattering, transmission electron microscopy, and optical microscopy. The constituent block copolymers of the mixture have almost same molecular weights but complementary compositions: one component (designated as i-2K) has a number-average molecular weight (Mn) of 1.2 × 104 and its volume fraction of PS (fPS) is 0. 81, and the other component (designated as s-3K) is Mn = 1.3 × 104 and fPS = 0.21; both neat i-2K and neat s-3K are in disordered state at all temperatures covered in this experiment. The macrophase transition temperature for the i-2K/s-3K = 50/50(wt %/wt %) mixture was determined to be 130 °C, above which the mixture showed the two macrophase-separated disordered phases comp...