The synergistic effect during biphasic SET-LRP in ethanol–nonpolar solvent–water mixtures

Abstract

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 triphase in ethanol–water mixtures since poly(butyl acrylate) (PBA) is not soluble 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 containing Cu(II)Br₂ and hexamethylated tris(2-aminoethyl)amine (Me₆-TREN). 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 in the biphasic system, which was caused by the addition of hexanes that corresponds to a volumetric ratio of 4/3/3 for ethanol/hexanes/water, when the volume fraction of hexanes (ϕ_Hex) is constant at 0.3, and 4/4/2 while the volume fraction of water (ϕ_H2O) is constant at 0.2. Other nonpolar, non-disproportionating solvents such as ethyl acetate, toluene, anisole, diethyl carbonate and cyclohexane were all shown to mediate the SET-LRP of BA in ethanol–nonpolar solvent–water mixtures at a 4/4/2 (v/v/v) ratio. These experiments demonstrate for the first time the ability to use a diversity of non-disproportionating, nonpolar solvents in conjunction with miscible polar solvents and water in biphasic SET-LRP. This new methodology is important from mechanistic and also from technologic points of view since it expands the scope of polymer synthesis via SET-LRP from disproportionating to non-disproportionating nonpolar solvents.