Ultrafast SET-LRP in biphasic mixtures of the non-disproportionating solvent acetonitrile with water

Abstract

Acetonitrile is the classic polar solvent that does not disproportionate Cu(I)Br into Cu(0) and Cu(II)Br₂ even in the presence of a ligand that favors this disproportionation. Both Cu(0) powder and wire catalyzed the radical polymerization of methyl acrylate (MA) initiated with methyl 2-bromopropanoate (MBP) or bis(2-bromopropionyl)ethane (BPE) in acetonitrile in the presence of tris(2-dimethylaminoethyl)amine (Me₆-TREN), provides two first order kinetic regimes, incomplete monomer conversion and low polymer chain end(s) functionality. A solution of MA or n-butyl acrylate (BA) in acetonitrile forms a biphasic system when it is mixed with water containing Me₆-TREN or with a solution of Cu(II)Br₂ and Me₆-TREN in water. The addition of NaBH₄ to the biphasic system containing acetonitrile, monomer, Me₆-TREN, BPE or MBP, and Cu(II)Br₂ in water instantaneously reduces Cu(II)Br₂ to Cu(0) and in the presence of more than 5% water, transforms the two first order kinetic regimes into a single one that corresponds to single electron transfer living radical polymerization (SET-LRP). The rate of SET-LRP increases with the increased amount of water used in this two phase system to provide complete monomer conversion and polymers with close to quantitative chain end(s) functionality. This non-disproportionating polar solvent/water binary system expands the scope of SET-LRP to non-disproportionating polar solvents and is expected to also be generally useful for nonpolar solvents that do not disproportionate Cu(I)Br.