Self-Assembly of Monolayer Vesicles via Backbone-Shiftable Synthesis of Janus Core-Shell Bottlebrush Polymer

Abstract

We report the self-assembly of monolayer vesicles from Janus core-shell bottlebrush polymers. A route was developed to synthesize doubly grafted bottlebrush copolymers (DGBCPs) possessing A-b-B and B'-b-C side chains on a single repeating unit. Graft-through ring-opening metathesis polymerization of a norbornene moiety installed by single unit monomer insertion allowed us to place the backbone on any repeating unit of the core (B and B') block. By decorating each core chain end with different chains via reversible addition-fragmentation chain transfer polymerization, we can obtain nanoobjects with an asymmetric B core and a phase-separated A/C shell. We demonstrate that polystyrene-branch-polystyrene' and polylactide-b-polystyrene-branch-polystyrene'-b-poly(n-butyl acrylate) macromonomers can be successfully synthesized and polymerized to produce DGBCPs in high yields (81-94% conversion) with an absolute molar mass of 149-395 kg mol(-1) and a dispersity of 1.18-1.38. In a solvent slightly more selective to A than C, self-assembly of monolayer vesicles with diameter of <100 nm was observed by transmission electron microscopy. Dissipative particle dynamics simulations suggest that increasing the backbone length and moving the backbone toward the B'/C interface increases the backbone bending energy and favors a lower curvature. The spontaneous curvature appears to prefer a particular layer radius, avoiding bilayer formation.