Single Electron Transfer Living Radical Polymerization (SET-LRP) of Nonpolar Monomers in Triphasic and Biphasic Mixtures of Non-Disproportionating Solvents with Water

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Single Electron Transfer Living Radical Polymerization (SET-LRP)
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Single electron transfer-living radical polymerization (SET-LRP) of n-butyl acrylate (BA) catalyzed by Cu(0) generated via in situ reduction of Cu(II)Br2 with NaBH4 proceeds in ethanol-water mixtures as a triphasic system. This is due to the insolubility of poly(butyl acrylate) (PBA) in ethanol beyond a certain molecular weight and concentration. This triphase consists of the PBA gel swelled in the organic phase and the water phase. Addition of at least 10% hexanes or other nonpolar and non-disproportionating solvents to the ethanol-water reaction mixture transforms SET-LRP of BA from a triphasic to a biphasic system. A synergistic effect was observed for the biphasic system with added hexanes, when the volume fraction of water (𝜙water) was constant at 0.2. A maximum rate was observed with a volumetric ratio of 4/4/2 for ethanol/hexanes/water. Eliminating the disproportionation-promoting organic solvent (ethanol) and instead using a non-disproportionating organic solvent mixture would expand SET-LRP to a wider range of solvents. Acetone is an archetypal non-disproportionating solvent in SET-LRP and therefore its usage is currently limited. Here we report the elaboration of acetone-water biphasic mixtures as solvents for ultrafast SET-LRP that provides close to 100% conversion of methyl and n-butyl acrylates to the corresponding polymers with near quantitative chain-end functionality in 20 to 35 minutes at room temperature. These experiments demonstrate for the first time the ability to use a diversity of non-disproportionating, nonpolar solvents, in conjunction either with miscible polar solvents and water (ethanol/hexanes/water), or with just water (acetone/water), in biphasic SET-LRP. We expect that these results will help establish acetone, other ketones, and other nonpolar organic solvents as common solvents for metal-catalyzed LRPs of both hydrophobic and hydrophilic monomer.

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