Synthesis and design of double-hydrophilic copolymers for dextran/PEO water-in-water emulsion stabilization

Water-in-water (W/W) emulsions are formed by mixing incompatible aqueous polymer solutions. Their stabilization is more challenging in comparison with oil-in-water emulsions due to their extremely low interfacial tension, wide W/W interface and strong sensitivity to dilution. W/W emulsions cease to exist when diluted below the binodal curve, which significantly restricts their use in applications. This work aims to develop original double-hydrophilic grafted and diblock copolymers (DHGC and DHDC, respectively) based on dextran (Dex) and on poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA), a hydrophilic and PEO-philic polymer, to stabilize W/W emulsions made of Dex and polyethylene oxide (PEO) phases. A series of grafted and diblock copolymers (Dex-g-POEGMA and Dex-b-POEGMA) was synthesized by photo-mediated reversible addition-fragmentation chain transfer (photo-RAFT) polymerization using multifunctional and monofunctional dextran-based macromolecular chain transfer agents. Key parameters such as the molecular weight of OEGMA monomers, the lengths of Dex and POEGMA parts, and the grafting density were systematically varied. Results showed that Dex/PEO emulsion can be successfully stabilized, for at least one week, depending on the architecture and composition of the copolymers.