Visible Light and Sunlight Photoinduced ATRP with ppm of Cu Catalyst

Individual cell modification with cell surface specific atom transfer radical polymerization for enhanced Cr(VI) removal

Modifying cells with polymers on the surface can enable them to gain or enhance function with various applications, wherein the atom transfer radical polymerization (ATRP) has garnered significant potential due to its biocompatibility. However, specifically initiating ATRP from the cell surface for in-situ modification remains challenging. This study established a bacterial surface-initiated ATRP method and further applied it for enhanced Cr(VI) removal. The cell surface specificity was facilely achieved by cell surface labelling with azide substrates, following alkynyl ATRP initiator specifically anchoring with azide-alkyne click chemistry. Then, the ATRP polymerization was initiated from the cell surface, and different polymers were successfully applied to in-situ modification. Further analysis revealed that the modification of Shewanella oneidensis with poly (4-vinyl pyridine) and sodium polymethacrylate improved the heavy metal tolerance and enhanced the Cr(VI) removal rate of 2.6 times from 0.088 h-1 to 0.314 h-1. This work provided a novel idea for bacterial surface modification and would extend the application of ATRP in bioremediation.

ATRP with ppb Concentrations of Photocatalysts

In atom transfer radical polymerization (ATRP), dormant alkyl halides are intermittently activated to form growing radicals in the presence of a CuI/L/X-CuII/L (activator/deactivator) catalytic system. Recently developed very active copper complexes could decrease the catalyst concentration to ppm level. However, unavoidable radical termination results in irreversible oxidation of the activator to the deactivator species, leading to limited monomer conversions. Therefore, successful ATRP at a low catalyst loading requires continuous regeneration of the activators. Such a regenerative ATRP can be performed with various reducing agents under milder reaction conditions and with catalyst concentrations diminished in comparison to conventional ATRP. Photoinduced ATRP (PhotoATRP) is one of the most efficient methods of activator regeneration. It initially employed UV irradiation to reduce the air-stable excited X-CuII/L deactivators to the activators in the presence of sacrificial electron donors. Photocatalysts (PCs) can be excited after absorbing light at longer wavelengths and, due to their favorable redox potentials, can reduce X-CuII/L to CuI/L. Herein, we present the application of three commercially available xanthene dyes as ATRP PCs: rose bengal (RB), rhodamine B (RD), and rhodamine 6G (RD-6G). Even at very low Cu catalyst concentrations (50 ppm), they successfully controlled PhotoATRP. Well-defined polymers with preserved livingness were prepared under green LED irradiation, with subppm concentrations ([PC] ≥ 10 ppb) of RB and RD-6G or 5 ppm of RD. Interestingly, these PCs efficiently controlled ATRP at wavelengths longer than their absorption maxima but required higher loadings. Polymerizations proceeded with high initiation efficiencies, yielding polymers with narrow molecular weight distributions and high chain-end fidelity. UV-vis, fluorescence, and laser flash photolysis studies helped to elucidate the mechanism of the processes involved in the dual-catalytic systems, comprising parts per million of Cu complexes and parts per billion of PCs.

Photo-Deactivation Strategy for Switchable ATRP with the Assistance of Molecular Switches

Light irradiation is an external stimulus, rapidly developed in switchable atom transfer radical polymerization (ATRP) via photo-activation methods in recent years. Herein, a photo-deactivation strategy is introduced to regulate ATRP with the assistance of photoswitchable hexaarylbiimidozole (HABI). Under visible light irradiation and in the presence of HABI, ATRP is greatly decelerated or quenched depending on the concentration of HABI. Interestingly, with visible light off, ATRP can proceed smoothly and follow a first-order kinetics. Moreover, photo-switchable ATRP alternatively with light off and on is demonstrated. Besides, the mechanism of photo-deactivation ATRP involving radical quenching is proposed in the presence of HABI.

Highly efficient dual photoredox/copper catalyzed atom transfer radical polymerization achieved through mechanism-driven photocatalyst design

Atom transfer radical polymerization (ATRP) with dual photoredox/copper catalysis combines the advantages of photo-ATRP and photoredox-mediated ATRP, utilizing visible light and ensuring broad monomer scope and solvent compatibility while minimizing side reactions. Despite its popularity, challenges include high photocatalyst (PC) loadings (10 to 1000 ppm), requiring additional purification and increasing costs. In this study, we discover a PC that functions at the sub-ppm level for ATRP through mechanism-driven PC design. Through studying polymerization mechanisms, we find that the efficient polymerizations are driven by PCs whose ground state oxidation potential-responsible for PC regeneration-play a more important role than their excited state reducing power, responsible for initiation. This is verified by screening PCs with varying redox potentials and triplet excited state generation capabilities. Based on these findings, we identify a highly efficient PC, 4DCDP-IPN, featuring moderate excited state reducing power and a maximized ground state oxidation potential. Employing this PC at 50 ppb, we synthesize poly(methyl methacrylate) with high conversion, narrow molecular weight distribution, and high chain-end fidelity. This system exhibits oxygen tolerance and supports large-scale reactions under ambient conditions. Our findings, driven by the systematic PC design, offer meaningful insights for controlled radical polymerizations and metallaphotoredox-mediated syntheses beyond ATRP.

Antimony-Based Halide Perovskite Nanoparticles as Lead-Free Photocatalysts for Controlled Radical Polymerization

Metal halide perovskites have emerged as versatile photocatalysts to convert solar energy for chemical processes. Perovskite photocatalyzed polymerization draws special attention due to its straightforward synthesis process and the ability to create advanced perovskite-polymer nanocomposites. Herein, this work employs Cs3Sb2Br9 perovskite nanoparticles (NPs) as a lead-free photocatalyst for light-controlled atom transfer radical polymerization (ATRP). Cs3Sb2Br9 NPs exhibit high reduction potential and interact with electronegative bromide initiator with Lewis acid Sb sites, enabling efficient photoinduced reduction of initiators and controlled polymerization under blue light irradiation. Methacrylate monomers with various functional groups are successfully polymerized, and the resulting polymer showcased a dispersity (Đ) as small as 1.27. The living nature of polymerization is confirmed by high chain end fidelity and kinetic studies. Moreover, Cs3Sb2Br9 NPs serve as heterogeneous photocatalysts, demonstrating recyclability and reusability for up to four cycles. This work presents a promising approach to overcome the limitations of lead-based perovskites in photoinduced controlled radical polymerization, offering a sustainable and efficient alternative for the synthesis of well-defined polymeric materials.

Block Copolymers of Polyolefins with Polyacrylates: Analyzing and Improving the Blocking Efficiencies Using MILRad/ATRP Approach

Despite their industrial ubiquity, polyolefin-polyacrylate block copolymers are challenging to synthesize due to the distinct polymerization pathways necessary for respective blocks. This study utilizes MILRad, metal-organic insertion light-initiated radical polymerization, to synthesize polyolefin-b-poly(methyl acrylate) copolymer by combining palladium-catalyzed insertion-coordination polymerization and atom transfer radical polymerization (ATRP). Brookhart-type Pd complexes used for the living polymerization of olefins are homolytically cleaved by blue-light irradiation, generating polyolefin-based macroradicals, which are trapped with functional nitroxide derivatives forming ATRP macroinitiators. ATRP in the presence of Cu(0), that is, supplemental activators and reducing agents , is used to polymerize methyl acrylate. An increase in the functionalization efficiency of up to 71% is demonstrated in this study by modifying the light source and optimizing the radical trapping condition. Regardless of the radical trapping efficiency, essentially quantitative chain extension of polyolefin-Br macroinitiator with acrylates is consistently demonstrated, indicating successful second block formation.

Surface Functionalization with Polymer Brushes via Surface-Initiated Atom Transfer Radical Polymerization: Synthesis, Applications, and Current Challenges

Polymer brushes have received great attention in recent years due to their distinctive properties and wide range of applications. The synthesis of polymer brushes typically employs surface-initiated atom transfer radical polymerization (SI-ATRP) techniques. To realize the control of the polymerization process in different environments, various SI-ATRP techniques triggered by different stimuli have been developed. This review focuses on the latest developments in different stimuli-triggered SI-ATRP methods, such as electrochemically mediated, photoinduced, enzyme-assisted, mechanically controlled, and organocatalyzed ATRP. Additionally, SI-ATRP technology triggered by a combination of multiple stimuli sources is also discussed. Furthermore, the applications of polymer brushes in lubrication, biological applications, antifouling, and catalysis are also systematically summarized and discussed. Despite the advancements in the synthesis of various types of 1D, 2D, and 3D polymer brushes via controlled radical polymerization, contemporary challenges remain in the quest for more efficient and straightforward synthetic protocols that allow for precise control over the composition, structure, and functionality of polymer brushes. We anticipate the readers could promote the understanding of surface functionalization based on ATRP-mediated polymer brushes and envision future directions for their application in surface coating technologies.

Electrochemically Mediated Surface-Initiated Atom Transfer Radical Polymerization by ppm of CuII/Tris(2-pyridylmethyl)amine

Atom transfer radical polymerization (ATRP) is one of the most widely used methods for modifying surfaces with functional polymer films and has received considerable attention in recent years. Here, we report an electrochemically mediated surface-initiated ATRP to graft polymer brushes onto solid substrates catalyzed by ppm amounts of CuII/TPMA in water/MeOH solution. We systematically investigated the type and concentrations of copper/ligand and applied potentials correlated to the polymerization kinetics and polymer brush thickness. Gradient polymer brushes and various types of polymer brushes are prepared. Block copolymerization of 2-hydroxyethyl methacrylate (HEMA) and 3-sulfopropyl methacrylate potassium salt (PSPMA) (poly(HEMA-b-SPMA)) with ultralow ppm eATRP indicates the remarkable preservation of chain end functionality and a pronounced "living" characteristic feature of ppm-level eATRP in aqueous solution for surface polymerization.

Visible-light-induced ATRP under high-pressure: synthesis of ultra-high-molecular-weight polymers

In this study, a high-pressure-assisted photoinduced atom transfer radical polymerization (p ≤ 250 MPa) enabled the synthesis of ultra-high-molecular-weight polymers (UHMWPs) of up to 9 350 000 and low/moderate dispersity (1.10 < Đ < 1.46) in a co-solvent system (water/DMSO), without reaction mixture deoxygenation.

Thermoresponsive Coiled-Coil Peptide-Polymer Grafts

Alkyl halide side groups are selectively incorporated into monodispersed, computationally designed coiled-coil-forming peptide nanoparticles. Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) is polymerized from the coiled-coil periphery using photoinitiated atom transfer radical polymerization (photoATRP) to synthesize well-defined, thermoresponsive star copolymer architectures. This facile synthetic route is readily extended to other monomers for a range of new complex star-polymer macromolecules.

Red-Light-Driven Atom Transfer Radical Polymerization for High-Throughput Polymer Synthesis in Open Air

Photoinduced reversible-deactivation radical polymerization (photo-RDRP) techniques offer exceptional control over polymerization, providing access to well-defined polymers and hybrid materials with complex architectures. However, most photo-RDRP methods rely on UV/visible light or photoredox catalysts (PCs), which require complex multistep synthesis. Herein, we present the first example of fully oxygen-tolerant red/NIR-light-mediated photoinduced atom transfer radical polymerization (photo-ATRP) in a high-throughput manner under biologically relevant conditions. The method uses commercially available methylene blue (MB+) as the PC and [X-CuII/TPMA]+ (TPMA = tris(2-pyridylmethyl)amine) complex as the deactivator. The mechanistic study revealed that MB+ undergoes a reductive quenching cycle in the presence of the TPMA ligand used in excess. The formed semireduced MB (MB•) sustains polymerization by regenerating the [CuI/TPMA]+ activator and together with [X-CuII/TPMA]+ provides control over the polymerization. This dual catalytic system exhibited excellent oxygen tolerance, enabling polymerizations with high monomer conversions (>90%) in less than 60 min at low volumes (50-250 μL) and high-throughput synthesis of a library of well-defined polymers and DNA-polymer bioconjugates with narrow molecular weight distributions (Đ < 1.30) in an open-air 96-well plate. In addition, the broad absorption spectrum of MB+ allowed ATRP to be triggered under UV to NIR irradiation (395-730 nm). This opens avenues for the integration of orthogonal photoinduced reactions. Finally, the MB+/Cu catalysis showed good biocompatibility during polymerization in the presence of cells, which expands the potential applications of this method.

Photocatalytic ATRP Depolymerization: Temporal Control at Low ppm of Catalyst Concentration

A photocatalytic ATRP depolymerization is introduced that significantly suppresses the reaction temperature from 170 to 100 °C while enabling temporal regulation. In the presence of low-toxicity iron-based catalysts and under visible light irradiation, near-quantitative monomer recovery could be achieved (up to 90%), albeit with minimal temporal control. By employing ppm concentrations of either FeCl2 or FeCl3, the depolymerization during the dark periods could be completely eliminated, thus enabling temporal control and the possibility to modulate the rate by simply turning the light "on" and "off". Notably, our approach allowed preservation of the end-group fidelity throughout the reaction, could be carried out at high polymer loadings (up to 2M), and was compatible with various polymers and light sources. This methodology provides a facile, environmentally friendly, and temporally regulated route to chemically recycle ATRP-synthesized polymers, thus opening the door for further opportunities.

Visible-Light-Curable Acrylic Resins toward UV-Light-Blocking Adhesives for Foldable Displays

Current technological advances in the organic light-emitting diode panel design of foldable smartphones demand advanced adhesives with UV-blocking abilities, beyond their conventional roles of bonding objects and relieving deformation stress. However, optically clear adhesives (OCAs) with UV-blocking ability cannot be prepared using conventional UV-curing methods relying on a photoinitiator. Herein, a new acrylic resin that can be efficiently cured using visible light without oxygen removal is presented, which may be used to develop UV-blocking OCAs for use in current flexible displays. A novel photocatalyst and a specific combination of additives facilitate sufficiently rapid curing under visible light in the presence of UV-absorbers. Only a very small amount of the highly active photocatalyst is required to prepare UV-blocking OCA films with very high transparency in the visible region. Using this system, a UV-blocking OCA that nearly meets the specifications of an OCA used in commercialized foldable smartphones is realized. This technology can also be utilized in other applications that require highly efficient visible light curing, such as optically clear resins, dental resins, and 3D/4D-printable materials.

Solvent-Free Chemical Recycling of Polymethacrylates made by ATRP and RAFT polymerization: High-Yielding Depolymerization at Low Temperatures

Although controlled radical polymerization is an excellent tool to make precision polymeric materials, reversal of the process to retrieve the starting monomer is far less explored despite the significance of chemical recycling. Here, we investigate the bulk depolymerization of RAFT and ATRP-synthesized polymers under identical conditions. RAFT-synthesized polymers undergo a relatively low-temperature solvent-free depolymerization back to monomer thanks to the partial in situ transformation of the RAFT end-group to macromonomer. Instead, ATRP-synthesized polymers can only depolymerize at significantly higher temperatures (>350 °C) through random backbone scission. To aid a more complete depolymerization at even lower temperatures, we performed a facile and quantitative end-group modification strategy in which both ATRP and RAFT end-groups were successfully converted to macromonomers. The macromonomers triggered a lower temperature bulk depolymerization with an onset at 150 °C yielding up to 90 % of monomer regeneration. The versatility of the methodology was demonstrated by a scalable depolymerization (≈10 g of starting polymer) retrieving 84 % of the starting monomer intact which could be subsequently used for further polymerization. This work presents a new low-energy approach for depolymerizing controlled radical polymers and creates many future opportunities as high-yielding, solvent-free and scalable depolymerization methods are sought.

Visible Light-ATRP Driven by Tris(2-Pyridylmethyl)Amine (TPMA) Impurities in the Open Air

Atom transfer radical polymerization (ATRP) of oligo(ethylene oxide) monomethyl ether methacrylate (OEOMA500 ) in water is enabled using CuBr2 with tris(2-pyridylmethyl)amine (TPMA) as a ligand under blue or green-light irradiation without requiring any additional reagent, such as a photo-reductant, or the need for prior deoxygenation. Polymers with low dispersity (Đ = 1.18-1.25) are synthesized at high conversion (>95%) using TPMA from three different suppliers, while no polymerization occurred with TPMA is synthesized and purified in the laboratory. Based on spectroscopic studies, it is proposed that TPMA impurities (i.e., imine and nitrone dipyridine), which absorb blue and green light, can act as photosensitive co-catalyst(s) in a light region where neither pure TPMA nor [(TPMA)CuBr]+ absorbs light.

Comparison of Mechano- and PhotoATRP with ZnO Nanocrystals

Zinc oxide (ZnO) was previously reported as an excellent cocatalyst for mechanically controlled atom transfer radical polymerization (mechanoATRP), but its photocatalytic properties in photoinduced ATRP (photoATRP) have been much less explored. Herein, well-defined ZnO nanocrystals were prepared via microwave-assisted synthesis and applied as a heterogeneous cocatalyst in mechano- and photoATRP. Both techniques yielded polymers with outstanding control over the molecular weight, but ZnO-cocatalyzed photoATRP was much faster than analogous mechanoATRP (conversion of 91% in 1 h vs 54% in 5 h). The kinetics of photoATRP was tuned by loadings of ZnO nanocrystals. PhotoATRP with ZnO did not require any excess of ligand versus Cu, in contrast to mechanoATRP, requiring an excess of ligand, acting as a reducing agent. ZnO-cocatalyzed photoATRP proceeded controllably without prior deoxygenation, since ZnO was involved in a cascade of reactions, leading to the rapid elimination of oxygen. The versatility and robustness of the technique were demonstrated for various (meth)acrylate monomers with good temporal control and preservation of end-group functionality, illustrated by the formation of tailored block copolymers.

Fully Oxygen-Tolerant Visible-Light-Induced ATRP of Acrylates in Water: Toward Synthesis of Protein-Polymer Hybrids

Over the last decade, photoinduced ATRP techniques have been developed to harness the energy of light to generate radicals. Most of these methods require the use of UV light to initiate polymerization. However, UV light has several disadvantages: it can degrade proteins, damage DNA, cause undesirable side reactions, and has low penetration depth in reaction media. Recently, we demonstrated green-light-induced ATRP with dual catalysis, where eosin Y (EYH2) was used as an organic photoredox catalyst in conjunction with a copper complex. This dual catalysis proved to be highly efficient, allowing rapid and well-controlled aqueous polymerization of oligo(ethylene oxide) methyl ether methacrylate without the need for deoxygenation. Herein, we expanded this system to synthesize polyacrylates under biologically relevant conditions using CuII/Me6TREN (Me6TREN = tris[2-(dimethylamino)ethyl]amine) and EYH2 at ppm levels. Water-soluble oligo(ethylene oxide) methyl ether acrylate (average M n = 480, OEOA480) was polymerized in open reaction vessels under green light irradiation (520 nm). Despite continuous oxygen diffusion, high monomer conversions were achieved within 40 min, yielding polymers with narrow molecular weight distributions (1.17 ≤ D̵ ≤ 1.23) for a wide targeted DP range (50-800). In situ chain extension and block copolymerization confirmed the preserved chain end functionality. In addition, polymerization was triggered/halted by turning on/off a green light, showing temporal control. The optimized conditions also enabled controlled polymerization of various hydrophilic acrylate monomers, such as 2-hydroxyethyl acrylate, 2-(methylsulfinyl)ethyl acrylate), and zwitterionic carboxy betaine acrylate. Notably, the method allowed the synthesis of well-defined acrylate-based protein-polymer hybrids using a straightforward reaction setup without rigorous deoxygenation.

Recent Advances on Furan-Based Visible Light Photoinitiators of Polymerization

Photopolymerization is an active research field enabling to polymerize in greener conditions than that performed with traditional thermal polymerization. At present, a great deal of effort is devoted to developing visible light photoinitiating systems. Indeed, the traditional UV photoinitiating systems are currently the focus of numerous safety concerns so alternatives to UV light are being actively researched. However, visible light photons are less energetic than UV photons so the reactivity of the photoinitiating systems should be improved to address this issue. In this field, furane constitutes an interesting candidate for the design of photocatalysts of polymerization due to its low cost and its easy chemical modification. In this review, an overview concerning the design of furane-based photoinitiators is provided. Comparisons with reference systems are also established to demonstrate evidence of the interest of these photoinitiators in innovative structures.

Recent developments in visible light induced polymerization towards its application to nanopores

Visible light induced polymerizations are a strongly emerging field in recent years. Besides the often mild reaction conditions, visible light offers advantages of spatial and temporal control over chain growth, which makes visible light ideal for functionalization of surfaces and more specifically of nanoscale pores. Current challenges in nanopore functionalization include, in particular, local and highly controlled polymer functionalizations. Using spatially limited light sources such as lasers or near field modes for light-induced polymer functionalization is envisioned to allow local functionalization of nanopores and thereby improve nanoporous material performance. These light sources are usually providing visible light while classical photopolymerizations are mostly based on UV-irradiation. In this review, we highlight developments in visible light induced polymerizations and especially in visible light induced controlled polymerizations as well as their potential for nanopore functionalization. Existing examples of visible light induced polymerizations in nanopores are emphasized.

Excitation Dependence in Photoiniferter Polymerization

We report on a fundamental feature of photoiniferter polymerizations mediated with trithiocarbonates and xanthates. The polymerizations were found to be highly dependent on the activated electronic excitation of the iniferter. Enhanced rates of polymerization and greater control over molecular weights were observed for trithiocarbonate- and xanthate-mediated photoiniferter polymerizations when the n → π* transition of the iniferter was targeted compared to the polymerizations activating the π → π* transition. The disparities in rates of polymerization were attributed to the increased rate of C-S photolysis which was confirmed using model trapping studies. This study provides valuable insight into the role of electronic excitations in photoiniferter polymerization and provides guidance when selecting irradiation conditions for applications where light sensitivity is important.

Recent Advances in 3D Printing of Photocurable Polymers: Types, Mechanism, and Tissue Engineering Application

The conversion of liquid resin into solid structures upon exposure to light of a specific wavelength is known as photopolymerization. In recent years, photopolymerization-based 3D printing has gained enormous attention for constructing complex tissue-specific constructs. Due to the economic and environmental benefits of the biopolymers employed, photo-curable 3D printing is considered an alternative method for replacing damaged tissues. However, the lack of suitable bio-based photopolymers, their characterization, effective crosslinking strategies, and optimal printing conditions are hindering the extensive application of 3D printed materials in the global market. This review highlights the present status of various photopolymers, their synthesis, and their optimization parameters for biomedical applications. Moreover, a glimpse of various photopolymerization techniques currently employed for 3D printing is also discussed. Furthermore, various naturally derived nanomaterials reinforced polymerization and their influence on printability and shape fidelity are also reviewed. Finally, the ultimate use of those photopolymerized hydrogel scaffolds in tissue engineering is also discussed. Taken together, it is believed that photopolymerized 3D printing has a great future, whereas conventional 3D printing requires considerable sophistication, and this review can provide readers with a comprehensive approach to developing light-mediated 3D printing for tissue-engineering applications.

Cu(0)-RDRP of acrylates using an alkyl iodide initiator

In the vast majority of atom transfer radical polymerizations, alkyl bromides or alkyl chlorides are commonly employed as initiators. Herein, alkyl iodides are demonstrated as ATRP initiators.

PVDF-Based Fluoropolymer Modifications via Photoinduced Atom Transfer Radical Polymerizations

Graft modifications of PVDF fluoropolymers have been identified as the efficient route to improve the properties and expand the applications. Taking advantage of C-F and C-Cl bonds in the repeat units, atom transfer radical polymerizations (ATRP) were widely used for graft modification. Recently, photoinduced ATRP has shown good spatial and temporal control over the polymerization process in contrast to thermal activation mode. This minireview highlights the progress in PVDF-based fluoropolymer modifications by using photoinduced Cu(II)-mediated ATRP and organocatalyzed ATRP. The challenges and opportunities are proposed with the aim at advancing the development of synthesis and applications of fluoropolymer.

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.

Photoactive Copper Complexes: Properties and Applications

Photocatalyzed and photosensitized chemical processes have seen growing interest recently and have become among the most active areas of chemical research, notably due to their applications in fields such as medicine, chemical synthesis, material science or environmental chemistry. Among all homogeneous catalytic systems reported to date, photoactive copper(I) complexes have been shown to be especially attractive, not only as alternative to noble metal complexes, and have been extensively studied and utilized recently. They are at the core of this review article which is divided into two main sections. The first one focuses on an exhaustive and comprehensive overview of the structural, photophysical and electrochemical properties of mononuclear copper(I) complexes, typical examples highlighting the most critical structural parameters and their impact on the properties being presented to enlighten future design of photoactive copper(I) complexes. The second section is devoted to their main areas of application (photoredox catalysis of organic reactions and polymerization, hydrogen production, photoreduction of carbon dioxide and dye-sensitized solar cells), illustrating their progression from early systems to the current state-of-the-art and showcasing how some limitations of photoactive copper(I) complexes can be overcome with their high versatility.

N-Terminal Lysozyme Conjugation to a Cationic Polymer Enhances Antimicrobial Activity and Overcomes Antimicrobial Resistance

Microbial resistance to antibiotics is one of the greatest global healthcare challenges. There is an urgent need to develop effective strategies to overcome antimicrobial resistance. We, herein, report photoinduced in situ growth of a cationic polymer from the N-terminus of lysozyme. The attachment of the cationic polymer improves the proteolytic and thermal stability of lysozyme. Notably, the conjugate can efficiently overcome lysozyme resistance in Gram-positive bacteria and antibiotics-resistance in Gram-negative bacteria, which may be ascribed to the synergistic interactions of lysozyme and the cationic polymer with the bacteria to disrupt their cell membranes. In a rat periodontitis model, the lysozyme-polymer conjugate not only greatly outperforms lysozyme in therapeutic efficacy but also is superior to minocycline hydrochloride, which is the gold standard for periodontitis therapy. These findings may provide an efficient strategy to dramatically enhance the antimicrobial activities of lysozyme and pave a way to overcome antimicrobial resistance.

An aqueous photo-controlled polymerization under NIR wavelengths: synthesis of polymeric nanoparticles through thick barriers

We report an aqueous and near-infrared (NIR) light mediated photoinduced reversible addition-fragmentation chain transfer (photo-RAFT) polymerization system using tetrasulfonated zinc phthalocyanine (ZnPcS4 -) as a photocatalyst. Owing to the high catalytic efficiency and excellent oxygen tolerance of this system, well-controlled polyacrylamides, polyacrylates, and polymethacrylates were synthesized at fast rates without requiring deoxygenation. Notably, NIR wavelengths possess enhanced light penetration through non-transparent barriers compared to UV and visible light, allowing high polymerization rates through barriers. Using 6.0 mm pig skin as a barrier, the polymerization rate was only reduced from 0.36 to 0.21 h-1, indicating potential for biomedical applications. Furthermore, longer wavelengths (higher λ) can be considered an ideal light source for dispersion photopolymerization, especially for the synthesis of large diameter (d) nanoparticles, as light scattering is proportional to d 6/λ 4. Therefore, this aqueous photo-RAFT system was applied to photoinduced polymerization-induced self-assembly (photo-PISA), enabling the synthesis of polymeric nanoparticles with various morphologies, including spheres, worms, and vesicles. Taking advantage of high penetration and reduced light scattering of NIR wavelengths, we demonstrate the first syntheses of polymeric nanoparticles with consistent morphologies through thick barriers.

Electrochemical Investigation of Iron-Catalyzed Atom Transfer Radical Polymerization

Use of iron-based catalysts in atom transfer radical polymerization (ATRP) is very interesting because of the abundance of the metal and its biocompatibility. Although the mechanism of action is not well understood yet, iron halide salts are usually used as catalysts, often in the presence of nitrogen or phosphorous ligands (L). In this study, electrochemically mediated ATRP (eATRP) of methyl methacrylate (MMA) catalyzed by FeCl3, both in the absence and presence of additional ligands, was investigated in dimethylformamide. The electrochemical behavior of FeCl3 and FeCl3/L was deeply investigated showing the speciation of Fe(III) and Fe(II) and the role played by added ligands. It is shown that amine ligands form stable iron complexes, whereas phosphines act as reducing agents. eATRP of MMA catalyzed by FeCl3 was investigated in different conditions. In particular, the effects of temperature, catalyst concentration, catalyst-to-initiator ratio, halide ion excess and added ligands were investigated. In general, polymerization was moderately fast but difficult to control. Surprisingly, the best results were obtained with FeCl3 without any other ligand. Electrogenerated Fe(II) effectively activates the dormant chains but deactivation of the propagating radicals by Fe(III) species is less efficient, resulting in dispersity > 1.5, unless a high concentration of FeCl3 is used.

PET-RAFT Increases Uniformity in Polymer Networks

Photoinduced electron/energy transfer (PET)-reversible addition-fragmentation chain transfer polymerization (RAFT) and conventional photoinitiated RAFT were used to synthesize polymer networks. In this study, two different metal catalysts, namely, tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)₃) and zinc tetraphenylporphyrin (ZnTPP), were selected to generate two different catalytic pathways, one with Ir(ppy)₃ proceeding through an energy-transfer pathway and one with ZnTPP proceeding through an electron-transfer pathway. These PET-RAFT systems were contrasted against a conventional photoinitated RAFT process. Mechanically robust materials were generated. Using bulk swelling ratios and degradable cross-linkers, the homogeneity of the networks was evaluated. Especially at high primary chain length and cross-link density, the PET-RAFT systems generated more uniform networks than those made by conventional RAFT, with the electron transfer-based ZnTPP giving superior results to those of Ir(ppy)₃. The ability to deactivate radicals either by RAFT exchange or reversible coupling in PET RAFT was proposed as the mechanism that gave better control in PET-RAFT systems.

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.

Photoinduced Controlled/Living Polymerizations

The application of photochemistry in polymer synthesis is of interest due to the unique possibilities offered compared to thermochemistry, including topological and temporal control, rapid polymerization, sustainable low-energy processes, and environmentally benign features leading to established and emerging applications in adhesives, coatings, adaptive manufacturing, etc. In particular, the utilization of photochemistry in controlled/living polymerizations often offers the capability for precise control over the macromolecular structure and chain length in addition to the associated advantages of photochemistry. Herein, the latest developments in photocontrolled living radical and cationic polymerizations and their combinations for application in polymer syntheses are discussed. This Review summarizes and highlights recent studies in the emerging area of photoinduced controlled/living polymerizations. A discussion of mechanistic details highlights differences as well as parallels between different systems for different polymerization methods and monomer applicability.

Photoredox-Initiated Frontal Ring-Opening Metathesis Polymerization

Herein, we report the development of a photoredox-initiated frontal ring-opening metathesis polymerization (FROMP) chemical system. We found that a ruthenium-based, bis-N-heterocyclic carbene metathesis precatalyst was activated with 9-mesityl-10-phenylacridindium tetrafluoroborate, copper(II) triflate, and a 455 nm light source. This chemistry was used to initiate the FROMP of dicyclopentadiene; once initiated, the heat released from the polymerization sustained a well-controlled reaction front. Variation in copper or metathesis precatalyst loading yielded front speeds ranging from 0.15 to 0.43 mm s^-1 and front temperatures ranging from 140 to 205 °C. While the glass transition temperatures of the resultant polymers are lower than those derived with Grubbs' second-generation catalyst, this chemical system provides extended pot life.

Ultrafast Visible-Light-Induced ATRP in Aqueous Media with Carbon Quantum Dots as the Catalyst and Its Application for 3D Printing

Photoinduced atom transfer radical polymerization (ATRP) has been proved to be a versatile technique for polymer network formation. However, the slow polymerization rates of typical ATRP limited its application in the field of additive manufacturing (3D printing). In this work, we introduced carbon quantum dots (CQDs) for the first time to the ATRP in aqueous media and developed an ultrafast visible-light-induced polymerization system. After optimization, the polymerization could achieve a high monomer conversion (>90%) within 1 min, and the polydispersity index (PDI) of the polymer was lower than 1.25. This system was then applied as the first example of ATRP for the 3D printing of hydrogel through digital light processing (DLP), and the printed object exhibited good dimensional accuracy. Additionally, the excellent and stable optical properties of CQDs also provided interesting photoluminescence capabilities to the printed objects. We deduce this ATRP mediated 3D printing process would provide a new platform for the preparation of functional and stimuli-responsive hydrogel materials.

Simple Full-Spectrum Heterogeneous Photocatalyst for Photo-induced Atom Transfer Radical Polymerization (ATRP) under UV/vis/NIR and its Application for the Preparation of Dual Mode Curing Injectable Photoluminescence Hydrogel

The utilizing light with broadband range has attracted lots of research interest for the photo induced reversible-deactivation radical polymerization (RDRP). However, it is still a challenge for a single catalyst to simultaneously respond to various lights with highly varied wavelengths. Here, we proposed a simple strategy for the preparation of a heterogeneous photocatalyst suitable for photo induced atom transfer radical polymerization (photoATRP) under full spectrum (from UV/vis light to NIR), by combining pyridine nitrogen doped carbon dots (N-CDs) and upconversion nanoparticles (UCNPs). In the presence of these robust UCNP@SiO₂@N-CDs composite particles, the photoATRP could be carried on under the different irradiations of UV, blue, green, red, white, and 980 nm NIR light, with a low loading of part per million concentrations of the CuBr₂/L catalyst. Moreover, the excellent solvent and aqueous compatibility allow UCNP@SiO₂@N-CDs to be capable for photoATRP in both organic solvents and aqueous media, providing well-defined hydrophobic and hydrophilic polymers with low dispersity and excellent chain-end fidelity. In addition, the photoATRP with 980 nm NIR exhibited excellent penetrations through visible-light-proof barriers. The system could be used for the preparation of an injectable hydrogel that had dual curing and photoluminescence modes. Owing to the "living" characteristics of polymer chains achieved through ATRP, the hydrogel was capable to be easily repaired by using monomer as the binder.

Rational Design of Photocatalysts for Controlled Polymerization: Effect of Structures on Photocatalytic Activities

Over the past decade, the use of photocatalysts (PCs) in controlled polymerization has brought new opportunities in sophisticated macromolecular synthesis. However, the selection of PCs in these systems has been typically based on laborious trial-and-error strategies. To tackle this limitation, computer-guided rational design of PCs based on knowledge of structure-property-performance relationships has emerged. These rational strategies provide rapid and economic methodologies for tuning the performance and functionality of a polymerization system, thus providing further opportunities for polymer science. This review provides an overview of PCs employed in photocontrolled polymerization systems and summarizes their progression from early systems to the current state-of-the-art. Background theories on electronic transitions are also introduced to establish the structure-property-performance relationships from a perspective of quantum chemistry. Typical examples for each type of structure-property relationships are then presented to enlighten future design of PCs for photocontrolled polymerization.

Red-Light-Induced, Copper-Catalyzed Atom Transfer Radical Polymerization

Despite advances in photochemical atom transfer radical polymerization (photoATRP), these systems often rely on the use of UV light for the activation/generation of the copper-based catalytic species. To circumvent the problems associated with the UV light, we developed a dual photoredox catalytic system to mediate photoinduced ATRP under red-light irradiation. The catalytic system is comprised of a Cu catalyst to control the polymerization via ATRP equilibrium and a photocatalyst, such as zinc(II) tetraphenylporphine or zinc(II) phthalocyanine, to generate the activator Cu^I species under red-light irradiation. In addition, this system showed oxygen tolerance due to the consumption of oxygen in the photoredox reactions, yielding well-controlled polymerizations without the need for deoxygenation processes.

Thermally Degradable Poly(n-butyl acrylate) Model Networks Prepared by PhotoATRP and Radical Trap-Assisted Atom Transfer Radical Coupling

Model poly(n-butyl acrylate) (PBA) networks were prepared by photoinduced atom transfer radical polymerization (photoATRP), followed by curing of polymer stars via atom transfer radical coupling (ATRC) with a nitrosobenzene radical trap. The resulting nitroxyl radical installed thermally labile alkoxyamine functional groups at the junctions of the network. The alkoxyamine crosslinks of the network were degraded back to star-like products upon exposure to temperatures above 135 °C. Characterization of the degraded products via gel permeation chromatography (GPC) confirmed the inversion of polymer topology after thermal treatment.