Interfacial Raft-Like Structures From Bottlebrush Polymers

We investigated the interfacial behavior of amphiphilic random copolymer-grafted bottlebrush polymers (RC-BBPs) synthesized by copper-catalyzed azide-alkyne cycloaddition in a grafting-to approach. RC-BBPs stabilize the fluid-fluid interface by forming laterally confined, "raft-like" structures that anchor the side-chains parallel to the interface. These envisaged raft-like structures, when adsorbed to a fluid-fluid interface, are inferred to leave bare interfacial regions that are inaccessible to adsorption of additional rafts. As such, RC-BBPs prohibit dense interfacial packing and yield higher interfacial tensions and lower interfacial areal densities than compositionally uniform bottlebrush statistical copolymers (BSCPs). This interfacial assembly of bottlebrush polymer (BBP) rafts offers distinct advantages, since inter-raft gaps reflect a lack of close-packing that offers routes to mass transport, seen in this work as a >6-fold higher interfacial ion flux across RC-BBP-stabilized droplets relative to their BSCP counterparts. These results show that controlling the spatial distribution of BBPs via sequence randomness within the side-chains-a previously overlooked structural parameter-produces a distinct, sparsely packed assembly of BBPs that preserves bare interfacial area to yield regulated, patchy, selective, or adaptive liquid-liquid interfaces.