Non-Innocent Role of Sacrificial Anodes in Electrochemical Nickel-Catalyzed C(sp2)-C(sp3) Cross-Electrophile Coupling

Sacrificial anodes composed of inexpensive metals such as Zn, Fe, and Mg are widely used to support electrochemical nickel-catalyzed cross-electrophile coupling (XEC) reactions, in addition to other reductive electrochemical transformations. Such anodes are appealing because they provide a stable counter-electrode potential and typically avoid interference with the reductive chemistry. The present study outlines the development of an electrochemical Ni-catalyzed XEC reaction that streamlines access to a key pharmaceutical intermediate. Metal ions derived from sacrificial anode oxidation, however, directly contribute to homocoupling and proto-dehalogenation side products that are commonly formed in chemical and electrochemical Ni-catalyzed XEC reactions. Use of a divided cell limits interference by the anode-derived metal ions and supports a high product yield with negligible side product formation, introducing a strategy to overcome one of the main limitations of Ni-catalyzed XEC.

A guide to troubleshooting metal sacrificial anodes for organic electrosynthesis

The development of reductive electrosynthetic reactions is often enabled by the oxidation of a sacrificial metal anode, which charge-balances the reductive reaction of interest occurring at the cathode. The metal oxidation is frequently assumed to be straightforward and innocent relative to the chemistry of interest, but several processes can interfere with ideal sacrificial anode behavior, thereby limiting the success of reductive electrosynthetic reactions. These issues are compounded by a lack of reported observations and characterization of the anodes themselves, even when a failure at the anode is observed. Here, we weave lessons from electrochemistry, interfacial characterization, and organic synthesis to share strategies for overcoming issues related to sacrificial anodes in electrosynthesis. We highlight common but underexplored challenges with sacrificial anodes that cause reactions to fail, including detrimental side reactions between the anode or its cations and the components of the organic reaction, passivation of the anode surface by an insulating native surface film, accumulation of insulating byproducts at the anode surface during the reaction, and competitive reduction of sacrificial metal cations at the cathode. For each case, we propose experiments to diagnose and characterize the anode and explore troubleshooting strategies to overcome the challenge. We conclude by highlighting open questions in the field of sacrificial-anode-driven electrosynthesis and by indicating alternatives to traditional sacrificial anodes that could streamline reaction optimization.

Solvent Coordination Effect on Copper-Based Molecular Catalysts for Controlled Radical Polymerization

The equilibrium of copper-catalyzed atom transfer radical polymerization was investigated in silico with the aim of finding an explanation for the experimentally observed solvent effect. Various combinations of alkyl halide initiators and copper complexes in acetonitrile (MeCN) and dimethyl sulfoxide (DMSO) were taken into consideration. A continuum model for solvation, which does not account for the explicit interactions between the solvent and metal complex, is not adequate and does not allow the reproduction of the experimental trend. However, when the solvent molecules are included in the coordination sphere of the copper(I,II) species and the continuum description of the medium is still used, a solvent dependence of process thermodynamics emerges, in fair agreement with experimental trends.

Atom Transfer Radical Polymerization: A Mechanistic Perspective

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.

Toward Green Atom Transfer Radical Polymerization: Current Status and Future Challenges

Reversible-deactivation radical polymerizations (RDRPs) have revolutionized synthetic polymer chemistry. Nowadays, RDRPs facilitate design and preparation of materials with controlled architecture, composition, and functionality. Atom transfer radical polymerization (ATRP) has evolved beyond traditional polymer field, enabling synthesis of organic-inorganic hybrids, bioconjugates, advanced polymers for electronics, energy, and environmentally relevant polymeric materials for broad applications in various fields. This review focuses on the relation between ATRP technology and the 12 principles of green chemistry, which are paramount guidelines in sustainable research and implementation. The green features of ATRP are presented, discussing the environmental and/or health issues and the challenges that remain to be overcome. Key discoveries and recent developments in green ATRP are highlighted, while providing a perspective for future opportunities in this area.

Dual electrochemical and chemical control in atom transfer radical polymerization with copper electrodes

In Atom Transfer Radical Polymerization (ATRP), Cu⁰ acts as a supplemental activator and reducing agent (SARA ATRP) by activating alkyl halides and (re)generating the Cu^I activator through a comproportionation reaction, respectively. Cu⁰ is also an unexplored, exciting metal that can act as a cathode in electrochemically mediated ATRP (eATRP). Contrary to conventional inert electrodes, a Cu cathode can trigger a dual catalyst regeneration, simultaneously driven by electrochemistry and comproportionation, if a free ligand is present in solution. The dual regeneration explored herein allowed for introducing the concept of pulsed galvanostatic electrolysis (PGE) in eATRP. During a PGE, the process alternates between a period of constant current electrolysis and a period with no applied current in which polymerization continues via SARA ATRP. The introduction of no electrolysis periods without compromising the overall polymerization rate and control is very attractive, if large current densities are needed. Moreover, it permits a drastic charge saving, which is of unique value for a future scale-up, as electrochemistry coupled to SARA ATRP saves energy, and shortens the equipment usage.

The use of a Cu cathode in eATRP allows exploiting the synergistic effect between electrochemical and chemical stimuli to halt or accelerate polymerizations, reduce energy consumption and achieve control in challenging systems.

Aqueous electrochemically-triggered atom transfer radical polymerization

Simplified electrochemical atom transfer radical polymerization (seATRP) using Cu^II–N-propyl pyridineimine complexes (Cu^II(NPPI)₂) is reported for the first time. In aqueous solution, using oligo(ethylene glycol) methyl ether methacrylate (OEGMA), standard electrolysis conditions yield POEGMA with good control over molecular weight distribution (Đ_m < 1.35). Interestingly, the polymerizations are not under complete electrochemical control, as monomer conversion continues when electrolysis is halted. Alternatively, it is shown that the extent and rate of polymerization depends upon an initial period of electrolysis. Thus, it is proposed that seATRP using Cu^II(NPPI)₂ follows an electrochemically-triggered, rather than electrochemically mediated, ATRP mechanism, which distinguishes them from other Cu^IIL complexes that have been previously reported in the literature.

Simplified electrochemical atom transfer radical polymerization (seATRP) using Cu^II-pyridineimine complexes is reported and follows a previously unreported electrochemically triggered mechanism.

Current-controlled ‘plug-and-play’ electrochemical atom transfer radical polymerization of acrylamides in water

Aqueous electrochemical atom transfer radical polymerisation (eATRP) can be challenging due to deleterious side reactions leading to the loss of the ω-chain end, increased rates of activation (k¬act) leading to...

Exploring Electrochemically Mediated ATRP of Styrene

Electrochemically mediated atom transfer radical polymerization (eATRP) of styrene was studied in detail by using CuBr2/TPMA (TPMA = tris(2-pyridylmethyl)amine) as a catalyst. Redox properties of various Cu(II) species were investigated in CH3CN, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) both in the absence and presence of 50% (v/v) styrene. This investigation together with preliminary eATRP experiments at 80 °C indicated DMF as the best solvent. The effects of catalyst, monomer, and initiator concentrations were also examined. The livingness of the polymerization was studied by chain extension and electrochemical temporal control of polymerization.

Electrochemistry for Atom Transfer Radical Polymerization

Atom Transfer Radical Polymerization (ATRP) is the most powerful and most employed technology of Controlled Radical Polymerization (CRP) to produce polymers with well-defined architecture, that is, composition, topology, and functionality. Several hundreds of papers are published every year on ATRP processes, mainly based on empiric experimental procedures. Electrochemistry powerfully entered in the field of ATRP about 10 years ago, providing important contributions both to the further development of the process and to a better understanding of its mechanism. Five main issues took advantage of electrochemistry and/or its synergism with ATRP: i) understanding the mechanism of ATRP activation; ii) determination of thermodynamic parameters; iii) determination of activation and deactivation rate constants; iv) the SARA ATRP vs SET-LRP dispute: the role of Cu⁰ ; v) electrochemically-mediated ATRP.

Tuning dispersity of linear polymers and polymeric brushes grown from nanoparticles by atom transfer radical polymerization

Molecular weight distribution imposes considerable influence on the properties of polymers, making it an important parameter, impacting morphology and structural behavior of polymeric materials.

Electrochemically-initiated polymerization of reactive monomers via 4-fluorobenzenediazonium salts

We report on the electrochemically-initiated polymerization of reactive monomers using a fluorine-labelled aromatic diazonium salt in an undivided cell setup with subsequent post-polymerization modifications of the intact reactive moieties.

Catalytic Halogen Exchange in Supplementary Activator and Reducing Agent Atom Transfer Radical Polymerization for the Synthesis of Block Copolymers

Synthesis of block copolymers (BCPs) by catalytic halogen exchange (cHE) is reported, using supplemental activator and reducing agent Atom Transfer Radical Polymerization (SARA ATRP). The cHE mechanism is based on the use of a small amount of a copper catalyst in the presence of a suitable excess of halide ions, for the synthesis of block copolymers from macroinitiators with monomers of mismatching reactivity. cHE overcomes the problem of inefficient initiation in block copolymerizations in which the second monomer provides dormant species that are more reactive than the initiator. Model macroinitiators with low dispersity are prepared and extended to afford well-defined block copolymers of various compositions. Combined cHE/SARA ATRP is therefore a simple and potent polymerization tool for the copolymerization of a wide range of monomers allowing the production of tailored block copolymers.

Immobilization of laccase onto modified PU/RC nanofiber via atom transfer radical polymerization method and application in removal of bisphenol A

In this study, 2-hydroxyethyl methacrylate (HEMA) was used as the monomers for surface grafting on electrospun PU/RC nanofiber membrane via atom transfer radical polymerization (ATRP) method, and the PU/RC-poly(HEMA) nanofiber membrane was investigated as a carrier for LAC. Free and immobilized LAC was characterized, and efficiency of bisphenol A (BPA) removal was determined. The results indicated that the PU/RC-poly(HEMA)-LAC showed relatively higher pH stability, temperature stability, and storage stability than free and PU/RC-LAC; moreover, more than 60% of the PU/RC-poly(HEMA)-LAC activity was retained after 10 cycles of ABTS treatment. Notably, the BPA removal efficiency of PU/RC-poly(HEMA)-LAC membrane generally ranged from 87.3 to 75.4% for the five cycles. Therefore, the PU/RC-poly(HEMA) nanofiber membrane has great potential as a carrier for the LAC immobilization for various industrial applications and bioremediation.

Low Ppm Atom Transfer Radical Polymerization in (Mini)Emulsion Systems

In the last decade, unceasing interest in atom transfer radical polymerization (ATRP) has been noted, especially in aqueous dispersion systems. Emulsion or miniemulsion is a preferred environment for industrial polymerization due to easier heat dissipation and lower production costs associated with the use of water as a dispersant. The main purpose of this review is to summarize ATRP methods used in emulsion media with different variants of initiating systems. A comparison of a dual over single catalytic approache by interfacial and ion pair catalysis is presented. In addition, future development directions for these methods are suggested for better use in biomedical and electronics industries.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

Under pressure: electrochemically-mediated atom transfer radical polymerization of vinyl chloride

Electrochemically mediated ATRP (eATRP) of vinyl chloride (VC), a less activated monomer, was successfully achieved. It is the first report on eATRP of a gaseous monomer under pressure.

Modification of a polyethersulfone membrane with a block copolymer brush of poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) and a branched polypeptide chain of Arg–Glu–Asp–Val

Polyethersulfone (PES) has good thermal stability, superior pH, chlorine tolerance, and excellent chemical resistance; however, the hydrophilicity and biocompatibility of PES need to be improved for its real applications. In this study, we report a surface modification method for the preparation of a functional PES membrane with hydrophilic polymer chains (MPC and GMA) via surface-initiated electrochemically-mediated atom-transfer radical polymerization (SI-eATRP) technology, and the Arg–Glu–Asp–Val polypeptide groups (REDV) were immobilized onto the modified membrane by a ring-opening reaction. XPS and SEM were used to analyze the chemical composition and morphology of the modified membrane surfaces, confirming that the hydrophilic polymer chains MPC and GMA and the polypeptide group REDV were successfully grafted onto the PES membrane surface. The static water contact angle decreased from 89° to 50–65°, and the hydrophilic property of the modified membrane was enhanced. The water flux increased from 4.29 L m⁻² h⁻¹ for the pristine PES membrane to 25 L m⁻² h⁻¹ for the modified membrane with PGMA chains grafted on it and REDV functional groups immobilized on it; note that the antifouling tests showed that all the modified membranes had the higher flux recovery ratio values (FRR) of above 80% than the pristine PES membrane (about 60%), and the APTT for the modified membrane increased from 46 s to 93 s, indicating that these modified membranes could be applied in the separation and blood purification fields.

A block copolymer involving chains of poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) and Arg–Glu–Asp–Val was designed and used for modification of polymer membrane for applications in separation and blood purification field.

Electrochemically mediated ATRP in ionic liquids: controlled polymerization of methyl acrylate in [BMIm][OTf]

eATRP was successfully applied to methyl acrylate in [BMIm][OTf], then the PMMA-Br chain was extended with acrylonitrile under a catalytic halogen exchange.

Externally controlled atom transfer radical polymerization

ATRP can be externally controlled by electrical current, light, mechanical forces and various chemical reducing agents. The mechanistic aspects and preparation of polymers with complex functional architectures and their applications are critically reviewed.

Miniemulsion ARGET ATRP via Interfacial and Ion-Pair Catalysis: From ppm to ppb of Residual Copper

It was recently reported that copper catalysts used in atom transfer radical polymerization (ATRP) can combine with anionic surfactants used in emulsion polymerization to form ion pairs. The ion pairs predominately reside at the surface of the monomer droplets, but they can also migrate inside the droplets and induce a controlled polymerization. This concept was applied to activator regenerated by electron transfer (ARGET) ATRP, with ascorbic acid as reducing agent. ATRP of n-butyl acrylate (BA) and n-butyl methacrylate (BMA) was carried out in miniemulsion using CuII/tris(2-pyridylmethyl)amine (TPMA) as catalyst, with several anionic surfactants forming the reactive ion-pair complexes. The amount and structure of surfactant controlled both the polymerization rate and the final particle size. Well-controlled polymers were prepared with catalyst loadings as low as 50 ppm, leaving only 300 ppb of Cu in the precipitated polymer. Efficient chain extension of a poly(BMA)-Br macroinitiator confirmed high retention of chain-end functionality. This procedure was exploited to prepare polymers with complex architectures such as block copolymers, star polymers, and molecular brushes.

Preparation of protein imprinted polymers via protein-catalyzed eATRP on 3D gold nanodendrites and their application in biosensors

Sensitive detection of metalloproteins is very essential in human pathologies.

Electrochemical Atom Transfer Radical Polymerization in Miniemulsion with a Dual Catalytic System

An electrochemical approach was used to control atom transfer radical polymerization (ATRP) of n-butyl acrylate (BA) in miniemulsion. Electropolymerization required a dual catalytic system, composed of an aqueous phase catalyst and an organic phase catalyst. This allowed shuttling the electrochemical stimulus from the working electrode (WE) to the continuous aqueous phase and to the dispersed monomer droplets. As aqueous phase catalysts, the hydrophilic Cu complexes with the ligands N,N-bis( 2-pyridylmethyl)-2-hydroxyethylamine (BPMEA), 2,2'-bipyridine (bpy), and tris(2-pyridylmethyl)amine (TPMA) were tested. As organic phase catalysts, the hydrophobic complexes with the ligands bis(2-pyridylmethyl)-octadecylamine (BPMODA) and bis[2-(4-methoxy-3,5-dimethyl)-pyridylmethyl]octadecylamine (BPMODA*) were evaluated. Highest rates and best control of BA electropolymerization were obtained with the water-soluble Cu/BPMEA used in combination with the oil-soluble Cu/BPMODA*. The polymerization rate could be further enhanced by changing the potential applied at the WE. Differently from traditional ATRP systems, reactivity of the dual catalytic system did not depend on the redox potential of the catalysts but instead depended on the hydrophobicity and partition coefficient of the aqueous phase catalyst.