Synthesis of Krytox-PEG Copolymer Emulsion Stabilizer

The copolymer used to stabilize the primary emulsion (W₁/PFC) was synthesized using a two-step process, as seen in Fig. 1 and outlined in Holtze et al. (38 (link)). First, Krytox 157 FSL (DuPont, Wilmington, DE, USA) – a perfluoroether with carboxylic acid functionality – was converted to an acid chloride using methods previously described (39 , 40 ). Briefly, under a nitrogen purge, Krytox 157 FSL was added to a round bottom flask containing HFE-7100 (3M, St. Paul, MN, USA), a mixture of methyl nonafluoroisobutyl ether and methyl nonafluorobutyl ether. Thionyl chloride (Sigma Aldrich, St. Louis, MO, USA) was then added in a 10:1 molar excess relative to the Krytox 157 FSL. The flask was refluxed with a condenser and stirred for 24 hours at 50°C while under a nitrogen purge. The resulting mixture was concentrated using a rotary evaporator. Second, the acid chloride was reacted with polyoxyethylene (PEG) diamine (Sigma Aldrich) to form a copolymer, analogous to previously described methods (39 , 40 ). The solvent was a 5:3 volumetric ratio of HFE-7100 and benzotrifluoride (Alfa Aesar, Ward Hill, MA, USA). Similar experimental conditions were used as in the first reaction step. The resulting copolymer, termed Krytox-PEG copolymer, was concentrated using a rotary evaporator and its structure was confirmed using ¹H, ¹³C, and ¹⁹F NMR spectroscopy.