Synergistic Impact of Intra- and Interchain Dispersity on Block Copolymer Self-Assembly

The effect of chain length dispersity on self-assembly behaviors of block copolymers was quantitatively investigated. Two sets of binary blends with precisely controlled compositions were prepared by mixing A-homopolymers into AB2 linear-branched block copolymers, where the two B branches were of either equal or unequal lengths. The added A-homopolymers swell the corona A domain, resulting in a generic phase transition sequence as the volume fraction varies. The distribution of the A-homopolymers depends critically on their length relative to that of the A-block of the copolymers. Longer homopolymers tend to localize at the vertices of the Voronoi cells, while shorter ones distribute more evenly in the corona domain. While blends consisting of A-homopolymers and symmetric linear-branched block copolymers exhibit exclusively the cylindrical phase, the addition of A-homopolymers to asymmetric counterparts leads to a richer array of ordered structures, including the Frank–Kasper phases, quasicrystalline phases, and the hexagonally close-packed phase. The combination of architectural asymmetry in the core (intrachain dispersity) and the presence of A-homopolymers in the corona (interchain dispersity) synergistically stabilizes these exotic structures, which could not be achieved when these two effects were present individually.