Electrochemically Mediated Atom Transfer Radical Polymerization Employing Rapid Alternating Polarity

Mass transfer limitations pose considerable challenges in electrochemical synthesis, particularly in high-viscosity environments that are inherent to electrochemically mediated polymerizations. In such scenarios, inadequate transport of redox-active species to and from the electrode surface results in electrode fouling and premature termination of the polymerization. Herein, we have thoroughly investigated electrochemically mediated atom transfer radical polymerization (eATRP) as a model platform to address the challenges arising from mass transfer limitations associated with electrochemical polymerizations by employing rapid alternating polarity (rAP). In detail, we propose a straightforward strategy for eATRP employing readily available graphite electrodes within an undivided cell, and we implement a single constant alternating current on a millisecond time scale throughout the entire polymerization process. This method effectively prevents over-reduction of copper catalysts and electrode fouling, thereby facilitating the polymerizations of methyl acrylate with near-quantitative monomer conversions and exceptionally narrow dispersities (Đ < 1.1). Polymerization kinetics can be further regulated by tuning the applied current (I_app) and pulse duration. Most importantly, our approach allows eATRP to be performed with significantly reduced copper catalyst loading (2.5 ppm), while maintaining excellent control over polymerization, resulting in an ultrahigh molecular weight PMA (M_n = 1,598,000, Đ = 1.26). The monomer scope is extended to include methyl methacrylate and styrene. The high "livingness" and chain-end fidelity, as confirmed by the mass spectrometric analysis, enable the one-pot synthesis of a block copolymer PMMA-b-PMA and star-shaped polymer 4-star-PMA. This work could underpin future research on rAP in various controlled electrochemical polymerizations.