Bottlebrush Random Copolymers at Oil-Oil Interfaces

Oil-in-oil nonaqueous emulsions are of great interest for developing emulsion-templated polymers and encapsulation systems that are incompatible with water-sensitive substances. Tailor-made amphiphilic block copolymers are by far the most efficient stabilizers for oil-in-oil emulsions while less attention is given to copolymers with more complex architectures. Here, we report the stabilization of DMSO-silicone oil interface by bottlebrush random copolymers (BRCPs) containing norbornene backbones with densely grafted poly(methyl methacrylate) (PMMA) and polystyrene (PS) side chains. The assembly kinetics of BRCPs at the DMSO-silicone oil interface can be divided into three processes, including diffusion, reconfiguration and reorganization, and can be varied by tuning the degree of polymerization of the backbone (N_B). Due to the high efficiency of BRCPs in reducing the interfacial tension, when using BRCPs as stabilizers, stable silicone oil-in-DMSO traditional emulsions and high internal phase emulsions (HIPEs) can be successfully obtained, while no stable emulsions can be achieved with linear PMMA-b-PS serving as the stabilizer. This study, for the first time, underscores the great potential of amphiphilic bottlebrush copolymers in preparing oil-in-oil emulsions. Given the advances in polymerization strategy, a broad variety of amphiphilic bottlebrush copolymers are expected to be synthesized and applied in the stabilization of nonaqueous biphasic systems.