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

Block polymer self-assembly reflects a multiscale competition between enthalpic and entropic factors, producing periodic nanostructures with rich potential to tune the composition, geometry, and length scales. Until recently, the body-centered cubic lattice was believed to be the universal equilibrium state in the sphere-forming region. However, the recent discoveries of equilibrium Frank-Kasper σ and A15 phases in diblock polymer melts have revealed remarkable new complexity in these ostensibly simple materials. These complex low-symmetry phases have been experimentally identified in two types of neat block polymers: (1) linear AB diblocks and (2) linear ABA'C tetrablocks. To the best of our knowledge, non-linear architectures remain unexplored. In this talk, we will discuss the connections between molecular architecture and symmetry selection in block polymers. We have systematically tuned the architectural asymmetry in block polymers via living polymerization, from the linear-b-linear to linear-b-bottlebrush limits. Analysis by small-angle X-ray scattering provides insight into the impact of architectural asymmetry on block polymer self-assembly. Increasing the asymmetry between blocks skews the phase diagram and introduces new potential for block polymer design.