Microphase Separation of Particle-Forming AB/AC Diblock Copolymer Blends with Immiscible Core Blocks

The structural behavior of particle-forming binary blends of AB and AC diblock copolymer blends with common A block coronae and nearly immiscible core segments (B and C) is relatively unexplored. Such micelle blends are expected to either macrophase separate into AB-and AC-rich morphologies or to co-assemble into a single microphase-separated morphology, depending on the relative particle sizes of the individual diblocks. We synthesized asymmetric diblocks with poly(ethylene-alt-propylene) corona blocks and either poly(ethylene oxide) or poly(dimethylsiloxane) core segments and studied their blend morphologies using small-angle X-ray scattering (SAXS). When the two diblock particle sizes are well-matched, the blends assemble into single-phase BCC morphologies akin to intermetallic solid solutions. In blends with mismatched particle sizes, we observe the formation of either liquid-like packings of micelles, BCC solid solutions, or gradual evolution into a tetrahedrally close-packed C14 Laves phase. These findings provide insights into the phase evolution and future design of complex micelle morphologies of AB/AC block copolymer alloys.