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 (<i>e</i>ATRP) 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 <i>e</i>ATRP 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 (<i>Đ</i> < 1.1). Polymerization kinetics can be further regulated by tuning the applied current (<i>I</i>_app) and pulse duration. Most importantly, our approach allows <i>e</i>ATRP 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 (<i>M</i>_n = 1,598,000, <i>Đ</i> = 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-<i>b</i>-PMA and star-shaped polymer 4-<i>star</i>-PMA. This work could underpin future research on rAP in various controlled electrochemical polymerizations.