Atom transfer radical polymerization is a versatile technique for exerting precise control over polymer molecular weights, molecular weight distributions, and complex architectures. Here, we show that an externally applied electrochemical potential can reversibly activate the copper catalyst for this process by a one-electron reduction of an initially added air-stable cupric species (Cu(II)/Ligand). Modulation of polymerization kinetics is thereby tunable in real time by varying the magnitude of applied potential. Application of multistep intermittent potentials successfully triggers initiation of polymerization and subsequently toggles the polymerization between dormant and active states in a living manner. Catalyst concentrations down to 50 parts per million are demonstrated to maintain polymerization control manifested in linear first-order kinetics, a linear increase in polymer molecular weight with monomer conversion, and narrow polymer molecular weight distributions over a range of applied potentials.

Atom transfer radical polymerization (ATRP) methods were developed in water-based media, to grow polymers from proteins under biologically relevant conditions. These conditions gave good control over the resulting polymers, while still preserving the protein’s native structure. Several reaction parameters, such as ligand structure, halide species, and initiation mode were optimized in water and PBS buffer to yield well-defined polymers grown from bovine serum albumin (BSA), functionalized with cleavable ATRP initiators (I). The CuCl complex with ligand 2,2′-bipyridyne (bpy) provides the best conditions for the polymerization of oligo­(ethylene oxide) methacrylate (OEOMA) in water at 30 °C under normal ATRP conditions (I/CuCl/CuCl2/bpy = 1/1/9/22), while the CuBr/bpy complex gave better performance in PBS. Activators generated by electron transfer (AGET) ATRP gave well-controlled polymerization of OEOMA at 30 °C with the ligand tris­(2-pyridylmethyl)­amine (TPMA), (I/CuBr2/TPMA = 1/10/11). The AGET ATRP reactions required slow feeding of a very small amount of ascorbic acid into the aqueous reaction medium or buffer. The reaction conditions developed were used to create a smart, thermoresponsive, protein–polymer hybrid.

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Electrochemically mediated ATRP (eATRP) allows easy modulation of the overall rate and control of polymerization through the variation of an external applied potential, Eapp. This method has been successfully applied to aqueous ATRP of oligo(ethylene glycol) methyl ether methacrylate (OEOMA475) catalyzed by Cu/TPMA. Appropriate choice of Eapp allows the synthesis of POEOMA475 with high Mw, and narrow MW distribution

Initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) with ppm amount of Cu catalyst was successfully developed in water. For the first time, Cu catalyst concentrations of 100 ppm and lower were used in aqueous media to prepare well-defined macromolecules. Polymers of oligo(ethylene oxide) methyl ether acrylate were synthesized with low dispersity (M w /M n = 1.15−1.28) using 20−100 ppm of an active CuBr/tris(pyridin-2-ylmethyl)amine-based catalyst in the presence of excess bromide anions. This technique was used to synthesize a thermoresponsive block copolymer of poly(oligo(ethylene oxide) methyl ether methacrylate)-b-poly(oligo(ethylene oxide) methyl ether acrylate). The methacrylic block had a lower critical solution temperature (LCST = 77 ± 2 °C) below that of the acrylic block. The hydrodynamic diameter of ca. 10 nm at temperatures below the LCST is consistent with free polymer chains in solution, and the diameter of ca. 30 nm above the LCST is consistent with a micellar structure. The aqueous ICAR ATRP technique was also used to successfully synthesize a well-defined bioconjugate by growing poly(oligo(ethylene oxide) acrylate) from a bovine serum albumin (BSA) protein functionalized with ca. 30 ATRP initiating sites.