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Abstract Alternating current (AC) and pulsed electrolysis are gaining traction in electro(organic) synthesis due to their advantageous characteristics. We employed AC electrolysis in electrochemically mediated Atom Transfer Radical Polymerization (eATRP) to facilitate the regeneration of the activator Cu^Icomplex on Cu⁰electrodes. Additionally, Cu⁰served as a slow supplemental activator and reducing agent (SARA ATRP), enabling the activation of alkyl halides and the regeneration of the Cu^Iactivator through a comproportionation reaction. We harnessed the distinct properties of Cu⁰dual regeneration, both chemical and electrochemical, by employing sinusoidal, triangular, and square‐wave AC electrolysis alongside some of the most active ATRP catalysts available. Compared to linear waveform (DC electrolysis) or SARA ATRP (without electrolysis), pulsed and AC electrolysis facilitated slightly faster and more controlled polymerizations of acrylates. The same AC electrolysis conditions could successfully polymerize eleven different monomers across different mediums, from water to bulk. Moreover, it proved effective across a spectrum of catalyst activity, from low‐activity Cu/2,2‐bipyridine to highly active Cu complexes with substituted tripodal amine ligands. Chain extension experiments confirmed the high chain‐end fidelity of the produced polymers, yielding functional and high molecular‐weight block copolymers. SEM analysis indicated the robustness of the Cu⁰electrodes, sustaining at least 15 consecutive polymerizations. 

Since its inception, atom transfer radical polymerization (ATRP) has seen continuous evolution in terms of the design of the catalyst and reaction conditions; today, it is one of the most useful techniques to prepare well-defined polymers as well as one of the most notable examples of catalysis in polymer chemistry. This Perspective highlights fundamental advances in the design of ATRP reactions and catalysts, focusing on the crucial role that mechanistic studies play in understanding, rationalizing, and predicting polymerization outcomes. A critical summary of traditional ATRP systems is provided first; we then focus on the most recent developments to improve catalyst selectivity, control polymerizations via external stimuli, and employ new photochemical or dual catalytic systems with an outlook to future research directions and open challenges. 

Efficient transfer of halogen atoms is essential for controlling the growth of polymers in atom transfer radical polymerization (ATRP). The nature of halogens may influence the efficiency of the halogen atom transfer during the activation and deactivation processes. The effect of halogens can be associated with the C–X bond dissociation energy and the affinity of the halogens/halides to the transition metal catalyst. In this paper, we study the effect of halogens (Br vs. Cl) and reaction media in iron-catalyzed ATRP in the presence of halide anions as ligands. In Br-based initiating systems, polymerization of methacrylate monomers was well-controlled whereas Cl-based initiating systems provided limited control over the polymerization. The high affinity of the Cl atom to the iron catalyst renders it less efficient for fast deactivation of growing chains, resulting in polymers with molecular weights higher than predetermined by Δ[M]/[RX] o and with high dispersities. Conversely, Br can be exchanged with higher efficiency and hence provided good control over polymerization. Decreasing the polarity of the reaction medium improved the polymerization control. Polymerizations using ppm levels of the iron catalyst in acetonitrile (a more polar solvent) yielded polymers with larger dispersity values due to the slow rate of deactivation as opposed to the less polar solvent anisole, which afforded well-controlled polymers with dispersity <1.2. 

Temporal control in atom transfer radical polymerization (ATRP) relies on modulating the oxidation state of a copper catalyst, as polymer chains are activated by L/Cu I and deactivated by L/Cu II . (Re)generation of L/Cu I activator has been achieved by applying a multitude of external stimuli. However, switching the Cu catalyst off by oxidizing to L/Cu II through external chemical stimuli has not yet been investigated. A redox switchable ATRP was developed in which an oxidizing agent was used to oxidize L/Cu I activator to L/Cu II , thus halting the polymerization. A ferrocenium salt or oxygen were used to switch off the Cu catalyst, whereas ascorbic acid was used to switch the catalyst on by (re)generating L/Cu I . The redox switches efficiently modulated the oxidation state of the catalyst without sacrificing control over polymerization.