Tailoring Nanostructures Through Precise Architectural Engineering: Insights from Cyclic Block Copolymer...

A comprehensive understanding of the unique self-assembly potential of cyclic block copolymers has long been obscured by inherent molecular uncertainties, such as linear impurities and chain-length dispersity. This study addresses these challenges through meticulous design of discrete cyclic block copolymers and their precisely matched linear counterparts. Unconventional complex spherical packings, including Frank-Kasper A15 phase, σ phase, and a quasicrystalline phase, are captured, significantly broadening the structural diversity accessible in cyclic block copolymers. Direct comparisons among the topological isomers reveal substantially deflected phase boundaries and unexpected domain size expansion in cyclic block copolymers compared to their triblock counterparts, a trend that contradicts long-standing consensus. The discrepancies arise from a competition between two opposing factors: the enhanced conformational flexibility due to the elimination of chain ends and the steric hindrance imposed by the cyclic topology. When steric effects dominate, the increased conformational asymmetry in cyclic block copolymers stabilizes unconventional spherical phases and enlarges overall domain sizes. The precisely engineered macromolecules eliminate disruptive effects from confounding chemical defects, offering an ideal platform for systematic and quantitative investigation into how chain architecture governs self-assembly and molecular packing.