Impact of Architectural Asymmetry on Frank-Kasper Phase Formation in Block Copolymer Melts

Recent discoveries of complex low-symmetry phases in soft matter have inspired advances in molecular and materials design. However, understanding the mechanisms underlying symmetry selection across soft matter remains a challenge. Block polymers represent attractive model materials that permit wide synthetic tunability and provide access to multiple length scales. To date the block polymer design space has been largely limited to variations in molecular weight, block volume fraction, and conformational asymmetry. Molecular architecture offers rich potential but remains relatively unexplored in experimental block polymers. This work bridges this gap, connecting molecular architecture, space-filling demands, and symmetry selection in block polymer self-assembly. Three series of block polymers were synthesized by living polymerization, tuning the architectural asymmetry across the linear-b-linear and linear-b-bottlebrush limits. The bottlebrush architecture amplifies two key ingredients for the formation of Frank-Kasper phases: high conformational asymmetry and high self-concentration. Analysis by small-angle X-ray scattering provides insight into the impact of architectural asymmetry on block polymer self-assembly.