Engineering of Molecular Geometry in Bottlebrush Polymers

Bottlebrush polymers are large cylindrical macromolecules, where a molecular "width" emerges from a large number of side chains densely attached to a central backbone. The lengths of these grafted side chains exert indirect control over molecular flexibility, material processing, and molecular assembly behavior. Sequencing of the side-chain length is a promising route to further modify molecular geometry; however, tedious laboratory synthesis has imposed practical limits on this tunability. Here, we develop a methodology to overcome this limitation, leveraging automated synthesis and computer simulations to engineer bottlebrush polymers with three-dimensional molecular geometries. The automated flow synthesis platform combines fluid mechanics, reactor engineering, and living polymerization principles to gain precise synthetic control over the polymer architecture. Bottlebrush polymers with hourglass, football, bowtie, and sphere architecture profiles are synthesized with high molecular weights (up to 10⁶ g mol^-1, ∼150 nm) and narrow dispersities (Dϵ < 1.1). Atomic force microscopy and viscometry are used to illustrate the difference in the architecture of the polymers, providing results that match simulation predictions. This agreement enables the development of an inverse design protocol, where Monte Carlo simulations are used to correlate the molecular geometry for synthesis. This scalable synthetic strategy enables the production of designer macromolecules with any axisymmetric shape.