Water-in-Water Emulsions Based on Incompatible Polymers and Stabilized by Triblock Copolymers–Templated Polymersomes

Aqueous solutions containing a mixture of polyethylene glycol (PEG) and dextran homopolymers form an aqueous two-phase system which can be emulsified to give a water-in-water emulsion. We show how these emulsions can be stabilized using triblock polymers containing poly­[poly­(ethylene glycol) methyl ether methacrylate] (PEGMA), poly (<i>n</i>-butyl methacrylate) (BuMA), and poly­[2-(dimethylamino) ethyl methacrylate] (DMAEMA) blocks of general structure P_p-B_b-D_d, in which the middle BuMA block is hydrophobic. Low-energy input stirring of mixtures containing equal volumes of PEG- and dex-rich aqueous phases plus 1 wt % of P_p-B_b-D_d stabilizer all form dex-in-PEG emulsions (for the range of P_p-B_b-D_d triblock polymers used here) which have a polymersome-like structure. In favorable cases, the emulsion drop (or templated polymersome) sizes are a few micrometers and are stable for periods in excess of 6 months. The emulsions can be inverted from dex-in-PEG to PEG-in-dex by increasing the volume fraction of dex-rich aqueous phase. We demonstrate that both high and low molecular weight fluorescent solutes “self-load” into either the dex- or PEG-rich regions and that solute mass transfer across the water–water interface occurs on a timescale of less than 1 min