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.

Design, Synthesis, and Self‐Assembly of Janus Bottlebrush Polymers

“…[78][79][80] Later, relative more reports of grafting-through approaches were published than backbone-first strategy, in the benefit of norbornene (NB)-based macromonomers and ring-opening metathesis polymerization (ROMP). [53,56] Recently, combined grafting-to and grafting-from protocol was improved by the new design of multiple active sites and concurrent polymerizations. [57,81] Figure 1.…”

“…[ 6 ] An emerging Janus core–shell bottlebrush polymer has been developed by transferring the side chains from homo polymers to two different block copolymers. [ 53 ]…”

“…[ 32,33 ] The self‐assembly of Janus bottlebrush polymers achieves small domain size and tunable bulk property, [ 58,59 ] which is challenging for the traditional linear or bottlebrush polymers. [ 60,61 ] Therefore, Janus bottlebrush polymers have great potential applications in nanolithography, [ 58 ] photonic crystals, [ 62 ] biomedicine, [ 53 ] surfactants, [ 63 ] etc.…”

Synthesis of well‐defined norbornenyl‐terminated poly(alkyl methacrylate)s by group transfer polymerization and their grafting‐through ring‐opening metathesis polymerization

“…ROMP of highly lipophilic NB-PEHMA was evaluated in polar THF (entries 10-12) and nonpolar 1,2-dichloroethane (1,2-DCE) (entries 13-15); the solvent effect on bottlebrush polymer growth was profound. At a low [MM]/[G3] ratio of 50, the reaction in THF exhibited superior control compared to the reaction in 1,2-DCE, with a narrow unimodal molecular-weight distribution (entries 10 and 13, red lines in Figure 3a Finally, the polar macromonomer NB-PEEMA was evaluated (entries [16][17][18][19][20]. It exhibited a good conversion only in the case of [MM]/[G3] = 50 (94%, Entry 16), and quickly lost its polymerization efficiency as the ratio of macromonomer to G3 increased.…”

“…Furthermore, combined with the controlled/living synthesis of macromonomers, bottlebrush polymers possessing finely tuned structures and properties have become accessible. [15][16][17][18][19][20] The methacrylate polymer is among the most abundant polymers utilized in numerous applications, 21,22 and as such, it is surprising that its use in bottlebrush polymers extends to a few limited cases, especially involving the grafting-through process. Norbornenyl-terminated polymethacrylates are synthesized by anionic polymerization [23][24][25] or reversible-addition-fragmentation-transfer (RAFT) radical polymerization with a norbornene group containing an initiator or a terminator.…”