Kinetics of Atom Transfer Radical Polymerization

Microgel with a Core-Shell Particulate Structure Formed via Spinodal Decomposition of a Diblock Ionomer Containing a Doped Hydrophobic Moiety

This study explored the formation of soft colloidal particles from a diblock ionomer (DI) with the monomeric composition (acrylonitrile)x-co-(glycidyl methacrylate)y-b-(3-sulfopropyl methacrylate potassium)z-abbreviated as (AxGy)Sz, where x >> z > y. A colloidal dispersion was generated by introducing water into the pre-prepared DMSO solutions of DI, which led to micelle formation and subsequent coagulation. The assembly of the hydrophobic (AxGy) blocks was influenced by water content and chain conformational flexibility (the ability to adopt various forms of conformation). The resulting microgel structure (in particle form) consists of coagulated micelles characterized by discrete internal hydrophobic gel domains and continuous external hydrophilic gel layers. Characterization methods included light scattering, zeta potential analysis, and particle size distribution measurements. In contrast, the copolymer (AxGy) chains form random coil aggregates in DMSO-H2O mixtures, displaying a chain packing state distinct from the hydrophobic gel domains as aforementioned. Additionally, the amphiphilic glycidyl methacrylate (G) units within the (AxGy) block were found to modulate the microgel dimensions. Notably, the nanoscale hydrogel corona exhibits high accessibility to reactive species in aqueous media. The typical microgel has a spherical shape with a diameter ranging from 50 to 120 nm. It exhibits a zeta potential of -65 mV in a neutral aqueous medium; however, it may precipitate if the metastable colloidal dispersion state cannot be maintained. Its properties could be tailored through adjusting the internal chain conformation, highlighting its potential for diverse applications.

Bacteria-Mediated Intracellular Radical Polymerizations

Intracellular radical polymerizations allow for the direct bioorthogonal synthesis of various synthetic polymers within living cells, thereby providing a pathway to polymer-modified cells or the fermentative production of polymers. Here, we show that Escherichia coli cells can initiate the polymerization of various acrylamide, acrylic, and methacrylic monomers through an atom transfer radical reaction triggered by the activity of naturally occurring biomolecules within the bacterial cells. Intracellular radical polymerizations were confirmed by nuclear magnetic resonance spectroscopy, gel permeation chromatography of polymers extracted from the cells, and fluorescence labeling of the polymer directly inside the cells. The effect of polymerization on cell behavior and the response of the cells to polymerization was investigated through fluorescence microscopy and flow cytometry techniques, as well as metabolic and membrane integrity assays. The polymer synthesis and resulting products are cell-compatible, as indicated by the high viability of the polymerized cells. In cellulo synthesis of synthetic polymers containing fluorescent dyes was also achieved. These results not only enhance our understanding of the untapped potential of bacterial cells as living catalysts for polymer production but also reveal intracellular polymerization based on atom transfer radical polymerization initiators as a bioorthogonal tool for cell engineering and synthetic biology.

Visible light-triggered depolymerization of commercial polymethacrylates

The reversion of vinyl polymers with carbon-carbon backbones to their monomers represents an ideal path to alleviate the growing plastic waste stream. However, depolymerizing such stable materials remains a challenge, with state-of-the-art methods relying on "designer" polymers that are neither commercially produced nor suitable for real-world applications. In this work, we report a main chain-initiated, visible light-triggered depolymerization directly applicable to commercial polymers containing undisclosed impurities (e.g., comonomers, additives, or dyes). By in situ generation of chlorine radicals directly from the solvent, near-quantitative (>98%) depolymerization of polymethacrylates could be achieved regardless of their synthetic route (e.g., radical or ionic polymerization), end group, and molecular weight (up to 1.6 million daltons). The possibility to perform multigram-scale depolymerizations and confer temporal control renders this methodology a versatile and general route to recycling.

Polyethylene-poly(methyl acrylate) Block Copolymers from PACE-SARA ATRP: Utilizing Polyolefin Active Ester Exchange-Based Macroinitiators in Atom Transfer Radical Polymerization

Accessing a facile pathway to prepare polyolefin-polar block copolymers with low dispersity and high control remains a challenge due to the distinct polymerization pathways of the composing blocks. This study utilized the polyolefin active ester exchange, the PACE approach, as a viable solution. The PACE approach, using palladium-catalyst-based coordination-insertion polymerization, was combined with SARA ATRP (supplemental activator/reducing agent atom transfer radical polymerization). A single-chain-end active ester functionalized polyethylene (PE) was produced from an α-diimine Pd(II) hexafluoroisopropyl ester chelate complex, which facilitated a living polymerization of ethylene. Transesterification with 2-hydroxyethyl α-bromoisobutyrate (HOBIB) or 2-hydroxyethyl α-bromoisobutyramide (HOBIBA) formed α-bromoisobutyrate or α-bromoisobutyramide chain-end-functionalized polyethylene. The approach resulted in controlled synthesis of polymers with low dispersity (Đ), high initiation efficiency, and high reproducibility. Both the amide-linked and ester-linked macroinitiators showed >90% initiation efficiency and Đ values of block copolymers as low as 1.05. This work demonstrated a successful combination of two living polymerization techniques, an insertion and controlled radical polymerization, unified in PACE-SARA ATRP, offering access to polyolefin-containing block copolymers with chemically distinct structures.

Better Together: Photoredox/Copper Dual Catalysis in Atom Transfer Radical Polymerization

Photomediated Atom Transfer Radical Polymerization (photoATRP) is an activator regeneration method, which allows for the controlled synthesis of well-defined polymers via light irradiation. Traditional photoATRP is often limited by the need for high-energy ultraviolet or violet light. These could negatively affect the control and selectivity of the polymerization, promote side reactions, and may not be applicable to biologically relevant systems. This drawback can be circumvented by an introduction of the catalytic amount of photocatalysts, which absorb visible and/or NIR light and, therefore, controlled, regenerative ATRP can be performed with the dual-catalytic cycle. Herein, a critical summary of recent developments in the field of dual-catalysis concerning Cu-catalyzed ATRP is provided. Contributions of involved species are examined mechanistically, followed by challenges and future directions towards the next generation of advanced functional macromolecular materials.

Photo-crosslinked Diels-Alder and thiol-ene polymer networks

Compositions of ethylene glycol dicyclopentenyl ether methacrylate (EGDEMA), a vegetable oil based alkyl methacrylate (C13MA), and furfuryl methacrylate (FMA) were terpolymerized for dual-crosslinked networks with tailored mechanical and thermal properties. Specifically, initiators for continuous activator regeneration (ICAR) atom transfer radical polymerization (ATRP) afforded materials with tailored glass transition temperature (T g) and incorporation of furan and norbornene functionalities within a single chain. The terpolymer with high furan and norbornene functionality (Ter2: F FMA = 0.42, F EGDEMA = 0.46, F C13MA = 0.12) is crosslinked to form single-crosslinked reversible networks with 1,1'-(methylenedi-4,1-phenylene)bismaleimide (BM) via Diels-Alder (DA) chemistry and dual-crosslinked networks incorporating additional non-reversible thiol-ene crosslinks. The reactions were photo-initiated using 254 nm UV light with BM : FMA molar ratios of 0.1 and 0.2 for both systems. FTIR analyses for crosslinked Ter2 samples confirmed the successful formation of DA and thiol-ene adducts, while DSC confirmed the reversibility of the DA reaction. A terpolymer with higher C13MA composition (Ter3: F C13MA = 0.75, F FMA = 0.17, F EGDEMA = 0.08) was similarly crosslinked in single and dual crosslinked networks with BM : FMA of 0.1 and 0.2. Crosslinking efficiency was evaluated for both single and dual crosslinked networks with a BM : FMA = 0.1 by comparing thermal and UV curing methods, with UV curing proving more effective for dual-crosslinked systems, leading to increased gel content (71% with UV compared to 61% thermally) and improved material properties. FTIR and DSC results confirmed the formation of the DA adducts and the reversibility of the DA reaction. The terpolymers were further analyzed for adhesive applications through rheological testing. These studies demonstrated that the incorporation of thiol-ene crosslinking alongside Diels-Alder crosslinking offers a balanced combination of reversible and permanent bonds, resulting in materials with enhanced mechanical strength, thermal stability, and functional versatility that are suitable for applications such as recyclable adhesives.

Could Olympic Gels of Polystyrene be Produced by ARGET ATRP From Bifunctional Initiators?

The kinetics of gelation in the Activators Regenerated by Electron Transfer Atom Transfer Radical Polymerization (ARGET ATRP) of styrene, using a bifunctional initiator and no crosslinking agents are investigated. By applying the method of moments, we develop a system of differential equations that accounts for the formation of polymer rings. The kinetic rate constants of this model are optimized on the experimentally determined kinetics, varying the reaction temperature and ethanol fraction. Subsequently, we explore how variations in the amounts of catalyst, initiator, and reducing agents affect the simulated equilibria of ARGET ATRP, the emergence of gelation, and the swelling properties of the resulting networks. These findings suggest that favoring ring formation enhances the gelation phenomenon, supporting the hypothesis that the networks formed under the reported reaction conditions are olympic gels.

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.

One Reaction: Two Types of Mechanism-SARA-ATRP and SET-LRP-for MMA Polymerization in the Presence of PVC

This study presents for the first time the polymerization of methyl methacrylate (MMA) in the presence of poly(vinyl chloride) (PVC) that takes place by both SARA-ATRP and SET-LRP mechanisms. The two types of polymerizations that occur in the system are PMMA grafting to the PVC backbone and the formation of a new PMMA polymer, both occurring in the presence of a Cu0wire. The polymerizations were controlled as confirmed by the molecular weight evolution, polymerization kinetics, and variations in the dispersity value. The MMA polymerization in the presence of PVC at 60 and 70 °C leads to the formation of two polymer species characterized by an increase in the molecular weight with the conversion and a narrowing of the dispersity value with the reaction progress. To increase the degree of control over the polymerization, the same reaction was performed at room temperature, which allowed us to highlight the presence of the SARA-ATRP and SET-LRP mechanisms via subsequent polymer chain extensions. The results demonstrated that PMMA grafting on PVC polymers follows a SARA-ATRP mechanism, while the formation of a PMMA homopolymer entails a SET-LRP process. The influence of solvent nature on the polymerization reaction was studied by performing the grafting of N-isopropylacrylamide (NIPAM) onto the surface of PVC particles in aqueous media in the presence and in the absence of CuCl2. The polymerization reactions and the obtained materials were studied by gel permeation chromatography (GPC), 1H NMR, DMA, scanning electron microscopy (SEM), and atomic force microscopy (AFM).

Electrochemically Mediated Atom Transfer Radical Polymerization Driven by Alternating Current

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 CuI complex on Cu0 electrodes. Additionally, Cu0 served as a slow supplemental activator and reducing agent (SARA ATRP), enabling the activation of alkyl halides and the regeneration of the CuI activator through a comproportionation reaction. We harnessed the distinct properties of Cu0 dual 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 Cu0 electrodes, sustaining at least 15 consecutive polymerizations.

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.

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.

Regulating Charge Carrier Dynamics in Stable Perovskite Nanorods for Photo-Induced Atom Transfer Radical Polymerization

Semiconducting nanocrystals have attracted world-wide research interest in artificial photosynthesis due to their appealing properties and enticing potentials in converting solar energy into valuable chemicals. Compared to 0D nanoparticles, 1D nanorods afford long-distance charge carriers separation and extended charge carriers lifetime due to the release of quantum confinement in axial direction. Herein, stable CsPbBr3 nanorods of distinctive dimensions are crafted without altering their properties and morphology via grafting hydrophobic polystyrene (PS) chains through a post-synthesis ligand exchange process. The resulting PS-capped CsPbBr3 nanorods exhibit a series of enhanced stabilities against UV irradiation, elevated temperature, and polar solvent, making them promising candidates for photo-induced atom transfer radical polymerization (ATRP). Tailoring the surface chemistry and dimension of the PS-capped CsPbBr3 nanorods endows stable, but variable reaction kinetics in the photo-induced ATRP of methyl methacrylate. The trapping-detrapping process of photogenerated charge carriers lead to extended lifetime of charge carriers in lengthened CsPbBr3 nanorods, contributing to a facilitated reaction kinetics of photo-induced ATRP. Therefore, by leveraging such stable PS-capped CsPbBr3 nanorods, the effects of surface chemistry and charge carriers dynamics on its photocatalytic performance are scrutinized, providing fundamental understandings for designing next-generation efficient nanostructured photocatalyst in artificial photosynthesis and solar energy conversion.

ATRP catalysts of tetradentate guanidine ligands - do guanidine donors induce a faster atom transfer?

Tripodal tetradentate N donor ligands stabilise the most active ATRP catalyst systems. Here, we set out to synthesise the new guanidine ligand TMG-4NMe2uns-penp, inspired by p-substituted tris(2-pyridylmethyl)amine (TPMA) ligands. The impact of changing pyridine against guanidine donors was examined through solid state and solution experiments and density functional theory (DFT) calculations. In the solid state, the molecular structures of copper complexes based on the ligands TMG-4NMe2uns-penp, TMG-uns-penp and TMG3tren were discussed concerning the influence of a NMe2 substituent at the pyridines and the guanidine donors. In solution, the TMG-4NMe2uns-penp system was investigated by several methods, including UV/Vis, EPR and NMR spectroscopy indicating similar properties to that of the highly active TPMANMe2 system. The redox potentials were determined and related to the catalytic activity. Besides the expected trends between these and the ligand structures, there is evidence that guanidine donors in tripodal ligand systems lead to a better deactivation and possibly a faster exchange within the ATRP equilibrium than TPMA systems. Supported by DFT calculations, it derives from an easier cleavable Cu-Br bond of the copper(II) deactivator species. The high activity was stated by a controlled initiator for continuous activator regeneration (ICAR) ATRP of styrene.

Robust Strategy to Improve the Compatibility between Incorporated Upconversion Nanoparticles and the Bulk Transparent Polymer Matrix

Traditional transparent polymer nanocomposites combined with functional fluorescent inorganic nanofillers are promising for many advanced optical applications. However, the aggregation of the incorporated functional nanoparticles results in light scattering and will decrease the transparency of nanocomposites, which will restrain the application of the transparent nanocomposites. Herein, a robust synthesis strategy was proposed to modify upconversion nanoparticles (UCNPs) with polymethyl methacrylate (PMMA) to form UCNP@PMMA core@shell nanocomposites though metal-free photoinduced surface-initiated atom transfer radical polymerization (photo-SI-ATRP), and thus, the dispersity of UCNP@PMMA and the interface compatibility between the surface of UCNPs and the bulk PMMA matrix was greatly improved. The obtained PMMA nanocomposites possess high transparency and show strong upconversion photoluminescence properties, which promises great opportunities for application in 3D display and related optoelectronic fields. This strategy could also be applied to fabricate other kinds of functional transparent polymer nanocomposites with inorganic nanoparticles uniformly dispersed.

Fast Bulk Depolymerization of Polymethacrylates by ATRP

Fast bulk depolymerization of poly(n-butyl methacrylate) and poly(methyl methacrylate), prepared by atom transfer radical polymerization (ATRP), is reported in the temperature range between 150 and 230 °C. Depolymerization of Cl-terminated polymethacrylates was catalyzed by a CuCl2/TPMA complex (0.022 or 0.22 equiv vs P-Cl) and was studied using TGA, also under isothermal conditions. Relatively rapid 5-20 min depolymerization was observed at 230 and 180 °C. The preparative scale reactions were carried out using a short-path distillation setup with up to 84% depolymerization within 15 min at 230 °C.

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.

Comparative Study of Polymer-Grafted BaTiO3 Nanoparticles Synthesized Using Normal ATRP as Well as ATRP and ARGET-ATRP with Sacrificial Initiator with a Focus on Controlling the Polymer Graft Density and Molecular Weight

Structurally well-defined polymer-grafted nanoparticle hybrids are highly sought after for a variety of applications, such as antifouling, mechanical reinforcement, separations, and sensing. Herein, we report the synthesis of poly(methyl methacrylate) grafted- and poly(styrene) grafted-BaTiO₃ nanoparticles using activator regeneration via electron transfer (ARGET ATRP) with a sacrificial initiator, atom transfer radical polymerization (normal ATRP), and ATRP with sacrificial initiator, to understand the role of the polymerization procedure in influencing the structure of nanoparticle hybrids. Irrespective of the polymerization procedure adopted for the synthesis of nanoparticle hybrids, we noticed PS grafted on the nanoparticles showed moderation in molecular weight and graft density (ranging from 30,400 to 83,900 g/mol and 0.122 to 0.067 chain/nm²) compared to PMMA-grafted nanoparticles (ranging from 44,620 to 230,000 g/mol and 0.071 to 0.015 chain/nm²). Reducing the polymerization time during ATRP has a significant impact on the molecular weight of polymer brushes grafted on the nanoparticles. PMMA-grafted nanoparticles synthesized using ATRP had lower graft density and considerably higher molecular weight compared to PS-grafted nanoparticles. However, the addition of a sacrificial initiator during ATRP resulted in moderation of the molecular weight and graft density of PMMA-grafted nanoparticles. The use of a sacrificial initiator along with ARGET offered the best control in achieving lower molecular weight and narrow dispersity for both PS (37,870 g/mol and PDI of 1.259) and PMMA (44,620 g/mol and PDI of 1.263) nanoparticle hybrid systems.

Kinetico-Mechanistic Studies on a Reactive Organocopper(II) Complex: Cu-C Bond Homolysis versus Heterolysis

Organocopper(II) reagents are an unexplored frontier of copper catalysis. Despite being proposed as reactive intermediates, an understanding of the stability and reactivity of the Cu^II-C bond has remained elusive. Two main pathways can be considered for the cleavage mode of a Cu^II-C bond: homolysis and heterolysis. We recently showed how organocopper(II) reagents can react with alkenes via radical addition, a homolytic pathway. In this work, the decomposition of the complex [Cu^IILR]⁺ [L = tris(2- dimethylaminoethyl)amine, Me₆tren, R = NCCH₂^-] in the absence and presence of an initiator (RX, X = Cl, Br) was evaluated. When no initiator was present, first-order Cu^II-C bond homolysis occurred producing [Cu^IL]⁺ and succinonitrile, via radical termination. When an excess of the initiator was present, a subsequent formation of [Cu^IILX]⁺ via a second-order reaction was found, which results from the reaction of [Cu^IL]⁺ with RX following homolysis. However, when Brønsted acids (R'-OH: R' = H, Me, Ph, PhCO) were present, heterolytic cleavage of the Cu^II-C bond produced [Cu^IIL(OR')]⁺ and MeCN. Kinetic studies were undertaken to obtain the thermal (ΔH^⧧, ΔS^⧧) and pressure (ΔV^⧧) activation parameters and deuterium kinetic isotopic effects, which provided an understanding of the strength of the Cu^II-C bond and the nature of the transition state for the reactions involved. These results reveal possible reaction pathways for organocopper(II) complexes relevant to their applications as catalysts in C-C bond forming reactions.

Development and Experimental Validation of a Dispersity Model for In Silico RAFT Polymerization

The exploitation of computational techniques to predict the outcome of chemical reactions is becoming commonplace, enabling a reduction in the number of physical experiments required to optimize a reaction. Here, we adapt and combine models for polymerization kinetics and molar mass dispersity as a function of conversion for reversible addition fragmentation chain transfer (RAFT) solution polymerization, including the introduction of a novel expression accounting for termination. A flow reactor operating under isothermal conditions was used to experimentally validate the models for the RAFT polymerization of dimethyl acrylamide with an additional term to accommodate the effect of residence time distribution. Further validation is conducted in a batch reactor, where a previously recorded in situ temperature monitoring provides the ability to model the system under more representative batch conditions, accounting for slow heat transfer and the observed exotherm. The model also shows agreement with several literature examples of the RAFT polymerization of acrylamide and acrylate monomers in batch reactors. In principle, the model not only provides a tool for polymer chemists to estimate ideal conditions for a polymerization, but it can also automatically define the initial parameter space for exploration by computationally controlled reactor platforms provided a reliable estimation of rate constants is available. The model is compiled into an easily accessible application to enable simulation of RAFT polymerization of several monomers.

Modelling Development in Radical (Co)Polymerization of Multivinyl Monomers

Radical polymerization (RP) of multivinyl monomers (MVMs) provides a facile solution for manipulating polymer topology and has received increasing attention due to their industrial and academic significance. Continuous efforts have been made to understand their mechanism, which is the key to regulating materials structure. Modelling techniques have become a powerful tool that can provide detailed information on polymerization kinetics which is inaccessible by experiments. Many publications have reported the combination of experiments and modelling for free radical polymerization (FRP) and reversible-deactivation radical polymerizations (RDRP) of MVMs. Herein, a minireview is presented for the most important modelling techniques and their applications in FRP/RDRP of MVMs. This review hopes to illustrate that the combination of modelling and wet experiments can be a great asset to polymer researchers and inspire new thinking for the future MVMs experiment optimization and product design.

Oxygen-Enhanced Atom Transfer Radical Polymerization through the Formation of a Copper Superoxido Complex

In controlled radical polymerization, oxygen is typically regarded as an undesirable component resulting in terminated polymer chains, deactivated catalysts, and subsequent cessation of the polymerization. Here, we report an unusual atom transfer radical polymerization whereby oxygen favors the polymerization by triggering the in situ transformation of CuBr/L to reactive superoxido species at room temperature. Through a superoxido ARGET-ATRP mechanism, an order of magnitude faster polymerization rate and a rapid and complete initiator consumption can be achieved as opposed to when unoxidized CuBr/L was instead employed. Very high end-group fidelity has been demonstrated by mass-spectrometry and one-pot synthesis of block and multiblock copolymers while pushing the reactions to reach near-quantitative conversions in all steps. A high molecular weight polymer could also be targeted (DP_n = 6400) without compromising the control over the molar mass distributions (Đ < 1.20), even at an extremely low copper concentration (4.5 ppm). The versatility of the technique was demonstrated by the polymerization of various monomers in a controlled fashion. Notably, the efficiency of our methodology is unaffected by the purity of the starting CuBr, and even a brown highly-oxidized 15-year-old CuBr reagent enabled a rapid and controlled polymerization with a final dispersity of 1.07, thus not only reducing associated costs but also omitting the need for rigorous catalyst purification prior to polymerization.

Covalent Mechanochemistry and Contemporary Polymer Network Chemistry: A Marriage in the Making

Over the past 20 years, the field of polymer mechanochemistry has amassed a toolbox of mechanophores that translate mechanical energy into a variety of functional responses ranging from color change to small-molecule release. These productive chemical changes typically occur at the length scale of a few covalent bonds (Å) but require large energy inputs and strains on the micro-to-macro scale in order to achieve even low levels of mechanophore activation. The minimal activation hinders the translation of the available chemical responses into materials and device applications. The mechanophore activation challenge inspires core questions at yet another length scale of chemical control, namely: What are the molecular-scale features of a polymeric material that determine the extent of mechanophore activation? Further, how do we marry advances in the chemistry of polymer networks with the chemistry of mechanophores to create stress-responsive materials that are well suited for an intended application? In this Perspective, we speculate as to the potential match between covalent polymer mechanochemistry and recent advances in polymer network chemistry, specifically, topologically controlled networks and the hierarchical material responses enabled by multi-network architectures and mechanically interlocked polymers. Both fundamental and applied opportunities unique to the union of these two fields are discussed.

Mechanically Driven Atom Transfer Radical Polymerization by Piezoelectricity

Targeting sustainable and eco-friendly polymer synthesis, we demonstrate here a synergistically catalyzed atom transfer radical polymerization (ATRP) induced and controlled by interplay between ball milling (BM) and piezoelectric nanoparticles (piezoNPs). BM-induced electron transfer can be achieved through piezoNPs deformation under impact force, serving as an external stimulus to mediate polymerization. The ppm level of copper loading is sufficient in fabrication of a polymer with well-defined molecular weight and low polydispersity. High-molecular-weight polymers ranging from 33 to 74 kDa were prepared successfully through DMSO-assisted grinding. Besides, its good performance on availability of water as liquid-assisted grinding additive, the recyclability of piezoNPs, and the formation of cross-linker-free composite resin make our ATRP approach a green and practical option alongside the existent heat-, electro-, and photo-induced methods.

PDMAEMA from α to ω chain ends: tools for elucidating the structure of poly(2-(dimethylamino)ethyl methacrylate)

An in-depth characterization of PDMAEMA prepared by ATRP was conducted, with a focus on end group analysis. This work discusses analytical tools providing essential information about the extent of control over DMAEMA polymerization and chain extension.

Highly Selective Radical Relay 1,4-Oxyimination of Two Electronically Differentiated Olefins

Radical addition reactions of olefins have emerged as an attractive tool for the rapid assembly of complex structures, and have plentiful applications in organic synthesis, however, such reactions are often limited to polymerization or 1,2-difunctionalization. Herein, we disclose an unprecedented radical relay 1,4-oxyimination of two electronically differentiated olefins with a class of bifunctional oxime carbonate reagents via an energy transfer strategy. The protocol is highly chemo- and regioselective, and three different chemical bonds (C-O, C-C, and C-N bonds) were formed in a single operation in an orchestrated manner. Notably, this reaction provides rapid access to a large variety of structurally diverse 1,4-oxyimination products, and the obtained products could be easily converted into valuable biologically relevant δ-hydroxyl-α-amino acids. With a combination of experimental and theoretical methods, the mechanism for this 1,4-oxyimination reaction has been investigated. Theoretical calculations reveal that a radical chain mechanism might operate in the reaction.

Understanding the structure-activity relationship and performance of highly active novel ATRP catalysts

Copper bromide complexes based on a series of substituted guanidine-quinolinyl and -pyridinyl ligands are reported. The ligand systems were chosen based on the large variation with regard to their flexibility in the backbone, different guanidine moieties and influence by electron density donating groups. Relationships between the molecular structures and spectroscopic and electronic properties are described. Beside the expected increase in activity by substituting the 4-position (NMe₂vs. H), we showed that a higher flexibility, such as TMG vs. DMEG moiety, leads to a better stabilsiation of the copper(II) complex. Due to the correlation of the potentials and K_ATRP values, the catalyst based on the ligand TMGm4NMe₂py is the most active copper complex for ATRP with a bidentate ligand system. The combination of the strong donating abilities of dimethylamine pyridinyl, the donor properties of the TMG substituent, and the improved flexibility due to the methylene bridging unit leads to high activity. With all NMe₂-substituted systems standard ATRP experiments were conducted and with more active NMe₂-substituted pyridinyl systems, ICAR ATRP experiments of styrene were conducted. Low dispersities and ideal molar masses have been achieved.

Efficacy analysis of new copper complex for visible light (455, 530 nm) radical/cationic photopolymerization: The synergic effects and catalytic cycle

The kinetics and the conversion features of two 3-component systems (A/B/N), based on the proposed new kinetic schemes of Mokbel and Mau et al, in which a visible LED is used to excite a copper complex to its excited triplet state (G*). The coupling of G* with iodonium salt and ethyl 4-(dimethylamino)benzoate (EDB) produces both free radical polymerization (FRP) of acrylates and the free radical promoted cationic polymerization (CP) of epoxides using various new copper complex as the initiator. Higher FRP and CP conversion can be achieved by co-additive of [B] and N, via the dual function of (i) regeneration [A], and (ii) generation of extra radicals. The interpenetrated polymer network (IPN) capable of initiating both FRP and CP in a blend of TMPTA and EPOX. The synergic effects due to CP include: (i) CP can increase viscosity limiting the diffusional oxygen replenishment; (ii) the cation also acts as a diluting agent for the IPN network, and (iii) the exothermic property of the CP. The catalytic cycle, synergic effects, and the oxygen inhibition are theoretically confirmed to support the experimental hypothesis. The measured results of Mokbel and Mau et al are well analyzed and matching the predicted features of our modeling.

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.

Tailoring Charge Separation at Meticulously Engineered Conjugated Polymer/Perovskite Quantum Dot Interface for Photocatalyzing Atom Transfer Radical Polymerization

In stark contrast to conventional organic ligand-capped counterparts, the ability to create stable metal halide perovskite nanocrystals strongly tethered with conjugated polymers (CPs) represents an important endeavor toward tailoring charge carrier dynamics at their interface that critically underpins applications of this unique class of all semiconducting, organic-inorganic nanomaterials for optoelectronics. This, however, has yet to be largely explored. Herein, we report, for the first time, the unraveling of efficient charge separation at judiciously designed CP/perovskite quantum dot (QD) interface for photoinduced atom transfer radical polymerization (p-ATRP). Such scrutiny is rendered by in situ crafting an array of monodisperse, highly stable, CP-ligated perovskite QDs with precisely controlled dimensions of each constituent via capitalizing on unimolecular, amphiphilic starlike block copolymers as nanoreactors. The intimate and permanent surface tethering of CPs imparts remarkable thermal, photo, and polar solvent stabilities of CP-ligated perovskite QDs. More importantly, they manifest efficient interfacial charge separation with a profound dependence on the length of ligated CPs and the size of perovskite QDs. The outstanding structural stabilities and charge separation characteristic enable CP-ligated perovskite QDs as robust photocatalysts for p-ATRP of a wide selection of monomers with stable and controllable reaction kinetics, also depending crucially on the length of CPs and the size of perovskite QDs. In principle, an exciting variety of CP-ligated, uniform perovskite QDs with virtually unlimited material choice of both markedly improved stabilities and tunable electronic band alignments can be readily accessed by exploiting the amphiphilic starlike block copolymer nanoreactor strategy for use in photodetectors, sensors, and LEDs, among other areas.

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.

Star Polymers vs. Dendrimers: Studies of the Synthesis Based on Computer Simulations

A generic model was developed for studies of the polymerization process of regular branched macromolecules. Monte Carlo simulations were performed employing the Dynamic Lattice Liquid algorithm to study this process. A core-first methodology was used in a living polymerization of stars with up to 32 arms, and dendrimers consisted of 4-functional segments. The kinetics of the synthesis process for stars with different numbers of branches and dendrimers was compared. The size and structure of star-branched polymers and dendrimers during the synthesis were studied. The influence of the functionality of well-defined cores on the structure and on the dispersity of the system was also examined. The differences in the kinetics in the formation of both architectures, as well as changes to their structures, were described and discussed.

Reverse atom transfer radical polymerization of dimethyl itaconate initiated by a new azo initiator: AIBME

Reverse atom transfer radical polymerization (RATRP) was used to synthesize poly(dimethyl itaconate) (PDMI) using an AIBME/CuBr₂/dNbpy system. The number average molecular weight (M _n) of PDMI was as high as M _n = 15 000 g mol^-1, the monomer conversion rate reached up to 70%, and the dispersity remained low (Đ = 1.06-1.38). The first-order kinetics of PDMI are discussed in detail. The AIBME initiator had a higher initiation efficiency than the AIBN initiator. As the ratio of initiator (AIBME) to catalyst (CuBr₂) decreased, the M _n and Đ of PDMI decreased. At 60 °C and 80 °C, the M _n of PDMI was much higher than the theoretical number average (M _n,th), and the Đ of PDMI broadened with the conversion rate. At 100 °C, the Đ of PDMI remained low, and the M _n of PDMI was closer to the M _n,th. As the ratio of monomer (DMI) to initiator (AIBME) increased, the M _n of PDMI changed little over time. These phenomena could be explained by the influence of the initiator and catalyst on polymerization kinetics.