Atom Transfer Radical Polymerization Mechanism Research Articles

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.

The Rational Design of Reducing Organophotoredox Catalysts Unlocks Proton-Coupled Electron-Transfer and Atom Transfer Radical Polymerization Mechanisms

Photocatalysis has become a prominent tool in the arsenal of organic chemists to develop and (re)imagine transformations. However, only a handful of versatile organic photocatalysts (PCs) are available, hampering the discovery of new reactivities. Here, we report the design and complete physicochemical characterization of 9-aryl dihydroacridines (9ADA) and 12-aryl dihydrobenzoacridines (12ADBA) as strong reducing organic PCs. Punctual structural variations modulate their molecular orbital distributions and unlock locally or charge-transfer (CT) excited states. The PCs presenting a locally excited state showed better performances in photoredox defunctionalization processes (yields up to 92%), whereas the PCs featuring a CT excited state produced promising results in atom transfer radical polymerization under visible light (up to 1.21 Đ, and 98% I*). Unlike all the PC classes reported so far, 9ADA and 12ADBA feature a free NH group that enables a catalytic multisite proton-coupled electron transfer (MS-PCET) mechanism. This manifold allows the reduction of redox-inert substrates including aryl, alkyl halides, azides, phosphate and ammonium salts (Ered up to -2.83 vs SCE) under single-photon excitation. We anticipate that these new PCs will open new mechanistic manifolds in the field of photocatalysis by allowing access to previously inaccessible radical intermediates under one-photon excitation.

12-Vertex closo-3,1,2-Ruthenadicarbadodecaboranes with Chelate POP-Ligands: Synthesis, X-ray Study and Electrochemical Properties

A class of so-called POP ligands (Xanthos, NiXantphos, DPEphos) are of a great interest to the coordination chemistry due to their wide P-M-P bite angles and ability to show either κ2- or κ3-binding modes. Such κ2–κ3-rearrangement is valuable for catalytic application and internal stabilization of intermediates. To widen the scope of ruthenium-based catalysts for Atom Transfer Radical Polymerization (ATRP) two new approaches to the synthesis of closo-ruthenacarboranes with aforementioned POP ligands were developed and six new 17-e (3,3-(POP)-3-Cl-closo-3,1,2-RuC2B9H11; 2, 4, 7) and 18-e (3,3-(POP)-3-NCCH3-closo-3,1,2-RuC2B9H11; 3, 5, 8) clusters were synthesized and characterized by means of NMR or ESR spectroscopy, MALDI mass-spectrometry and single crystal X-ray diffraction studies. The unique 18-e complex of Ru(II) with dioxygen ligand 3,3-(DPEphos)-3-(η2-O2)-closo-3,1,2-RuC2B9H11 (9) was isolated and characterized by X-ray diffraction. It was shown that aforementioned POP ligands coordinate to ruthenium by two phosphorus atoms in a κ2-fashion. The performed electrochemical studies have shown reversible Ru(II)-Ru(III) transition making the complexes suitable for application in catalysis of polymerization. The test experiments on methyl methacrylate (MMA) polymerization indicate the proceeding of the process in according with an ATRP mechanism.

Radical Lifetimes in Atom Transfer Radical Polymerization: A Monte Carlo and Deterministic Investigation

Mean radical lifetimes and fluctuations in lifetime are shown to decrease with conversion and polydispersity index for atom transfer radical polymerization (ATRP) of both methyl methacrylate and styrene. In the first study of its kind, a comprehensive investigation of radical lifetimes in both ATRP and conventional free-radical polymerizations is reported using a kinetic Monte Carlo model. Quantile–quantile plots show the radical lifetimes to be exponentially distributed with equal mean and standard deviation. Radical lifetimes are shown to be thousands of times longer in conventional free-radical polymerization compared with ATRP. Reduced mean radical lifetimes and fluctuations offer a new perspective on the ATRP mechanism. Reduction in radical lifetime fluctuations ensures less variability in the number of monomer units added during the propagation steps and keeps the polydispersity index low. Deterministic models are used along with the kinetic Monte Carlo model to investigate several facets of these polymerization systems and are validated against experimental data.

Determination of Monomer Reactivity Ratios in Controlled Copolymerization of Acrylonitrile with Unsaturated Methyl Esters

This paper reports the investigation of copolymerization of acrylonitrile with methyl acrylate, dimethyl maleate, dimethyl fumarate and dimethyl itaconate via atom transfer radical polymerization mechanism using copper bromide as a catalyst in combination with tris(2-pyridylmethyl)amine as a ligand. The reactivity ratios of monomers were evaluated using the Finemann–Ross and Kelen–Tudos methods basing on the copolymer composition determined by 1H NMR spectroscopy. It was found that reversible deactivation mechanism has no significant influence on the monomer reactivity ratios. It was found that among the tested comonomers methyl acrylate and dimethyl itaconate seem to be the most suitable ones for obtaining well-defined copolymers of acrylonitrile.

Regulating Gelation Time and Kinetics Analysis Based on the ARGET ATRP Mechanism

ABSTRACTA novel activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) initiation system composing of an initiator sodium chloroacetate, a catalyst ferric chloride, and a reducing agent ascorbic acid was developed to improve the gelation time of the in situ crosslinked polymer system. The kinetics of polymerization of acrylamide showed features of a living/controlled process in which the concentrations of the growing radicals [P·] are kept constant throughout the polymerization process. Compared with conventional potassium persulfate initiators, the gelation time of the in situ crosslinked polymer system can be improved to 40 h or even longer using the ARGET ATRP initiation system at 80 °C due to the low radical concentration and slow polymerization reaction. Core flooding test showed that the ARGET ATRP initiating system developed could initiate the polymerization reaction of the in situ crosslinked polymer system in the core. However, the gelation time was extended in comparison to that of the result obtained in the bottle, resulting from the dilution and adsorption of ARGET ATRP components during the injection process. The research expands the application field of the ARGET ATRP principle and has a promising prospect on controlling the gelation time of the in situ crosslinked polymer system. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 519–527

Atom Transfer Radical Polymerization: Billion Times More Active Catalysts and New Initiation Systems.

Approaching 25 years since its invention, atom transfer radical polymerization (ATRP) is established as a powerful technique to prepare precisely defined polymeric materials. This perspective focuses on the relation between structure and activity of ATRP catalysts, and the consequent choice of the initiating system, which are paramount aspects to well-controlled polymerizations. The ATRP mechanism is discussed, including the effect of kinetic and thermodynamic parameters and side reactions affecting the catalyst. The coordination chemistry and activity of copper complexes used in ATRP are reviewed in chronological order, while emphasizing the structure-activity correlation. ATRP-initiating systems are described, from normal ATRP to low ppm Cu systems. Most recent advancements regarding dispersed media and oxygen-tolerant techniques are presented, as well as future opportunities that arise from progressively more active catalysts and deeper mechanistic understanding.

SYNTHESIS OF POLYMERS BASED ON STEARYL METHACRYLATE AND THEIR USE AS ADDITIVES FOR DIESEL FUEL

In this article the features of controlled radical polymerization of stearyl methacrylate in the presence of copper-based compounds in combination with nitrogen-containing ligands such as tris[2-(dimethylamino)ethyl]amine and tris[(2-pyridyl)methyl]amine were studied. The ethyl 2-bromoisobutyrate was used as the initiator of the polymerization process. The synthesized polymers were characterized by gel permeation chromatography and MALDI-TOF time-of-flight mass spectrometry. It was found that the proposed catalytic systems allow conducting controlled radical polymerization of stearyl methacrylate according to the Atom Transfer Radical Polymerization mechanism at relatively mild temperature conditions. It was revealed that the nature of the organic ligand has a significant effect on the rate of polymerization and the molecular-weight characteristics of the synthesized samples. Using the copper(I) bromide catalytic system in combination with tris[(2-pyridyl)methyl]amine as a ligand at reagents molar ratio of 1:4, the polymerization of stearyl methacrylate proceeded with high reaction rate to deep conversions in a wide range of molecular weights. The observed linear growth of the molecular weight of the polymer with increasing conversion and low polydispersity index of the synthesized polymers being at the level of 1.19-1.29, considered as an evidence of the controlled mode of polymerization. The influence of the molecular weight characteristics of polymers based on stearyl methacrylate on the low-temperature properties of diesel fuel of specification24-2000 produced by OOO «LUKOIL-Nizhegorodnefteorgsintez» was evaluated using a low-temperature analyzer MX-700 (PE-7200I) in accordance with the requirements of Russian (GOST 5066-91 and GOST 20287-91) and the international (ISO-3016) standards for the quality of petroleum products. It was established that the synthesized polymers can be used as additives that reduce the temperature range of solidification of environmentally clean diesel fuels, while the molecular weight of polystearyl methacrylate has a significant effect on the depressor properties of the fuel.Forcitation:Simanskaya K.Yu., Grishin I.D., Grishin D.F. Synthesis of polymers based on stearyl methacrylate and their use as additives for diesel fuel. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 82-89

Predictive Tool for Design and Analysis of ARGET ATRP Grafting Reactions

Solving a comprehensive, yet simple, reaction model for describing the activators regenerated by electron transfer (ARGET)–atom transfer radical polymerization (ATRP) reaction cascade, we show that the molar ratios of transition metal catalyst to initiator and reducing agent to catalyst are critical parameters in the ARGET ATRP mechanism, with optimal values on the order of 0.1:1 and 10:1, respectively. The model also predicts an optimal molar ratio of reducing agent to initiator of 1:1. The ARGET ATRP reaction cascade is extremely complex with many adjustable species concentrations and reaction parameters. The effect of varying any of these parameters on the resulting temporal conversion trajectory of the polymerization is not straightforward. This analysis greatly simplifies the process allowing one to select the proper conditions to optimize the reaction and could save much effort, time and money. These results have severe implications when grafting polymer chains from surfaces, since the amount of sur...

Mechanism of Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization Mediated by Inorganic Sulfites: Experimental Measurements and Kinetic Simulations.

The mechanism of atom transfer radical polymerization (ATRP) mediated by sodium dithionite (Na2S2O4), with CuIIBr2/Me6TREN as catalyst (Me6TREN: tris[2-(dimethylamino)ethyl]amine)) in ethanol/water mixtures, was investigated experimentally and by kinetic simulations. A kinetic model was proposed and the rate coefficients of the relevant reactions were measured. The kinetic model was validated by the agreement between experimental and simulated results. The results indicated that the polymerization followed the SARA ATRP mechanism, with a SO2•- radical anion derived from Na2S2O4, acting as both supplemental activator (SA) of alkyl halides and reducing agent (RA) for CuII/L to regenerate the main activator CuI/L. This is similar to the reversible-deactivation radical polymerization (RDRP) procedure conducted in the presence of Cu0. The electron transfer from SO2•-, to either CuIIBr2/Me6TREN or R-Br initiator, appears to follow an outer sphere electron transfer (OSET) process. The developed kinetic model was used to study the influence of targeted degree of polymerization, concentration of CuIIBr2/Me6TREN and solubility of Na2S2O4 on the level of polymerization control. The presence of small amounts of water in the polymerization mixtures slightly increased the reactivity of the CuI/L complex, but markedly increased the reactivity of sulfites.

Development of a Robust Photocatalyzed ATRP Mechanism Exhibiting Good Tolerance to Oxygen and Inhibitors

A new photocatalyzed atom transfer radical polymerization (ATRP) procedure starting directly from a copper(II) bromine/phenanthroline (phen) mixture in the presence of triethylamine as a reducing agent is described. Under the irradiation of a compact blue LED lamp, the polymerization of methyl methacrylate (MMA) conducted to PMMAs with narrow molecular weights distributions (Mw/Mn ∼ 1.10). The good chain end fidelity of the products was validated in subsequent chain-extension experiments, using them as macroinitiators, either by conventional thermal ATRP or by photocatalyzed ATRP. The efficient reinitiation under light irradiation was also evidenced by a “light ON/OFF” experiment. The respective effects of several parameters on the polymerization kinetics were studied, including light intensity, the nature of the solvent, the molar ratio of the ligand, and the nature of the counterion. Besides the essential generation of the excited species [Cu(phen)2]+*, which will undergo an oxidative quenching as the k...

ATRP catalysed by ruthenacarboranes for successful synthesis of random and block-copolymers based on methacrylic monomers

The poly(methyl methacrylate) - based macroinitiator was successfully chain extended by isobornyl methacrylate, ethyl methacrylate and tert.-butyl methacrylate giving corresponding block-copolymers using catalytic system based on ruthenium carborane complex and isopropylamine. The polymerization proceeded smoothly in accordance with atom transfer radical polymerization mechanism giving polymers with predetermined molecular weights. A random copolymerization of methyl methacrylate, isobornyl methacrylate and tert.-butyl methacrylate was conducted using the same catalytic system. The measured glass transitions of obtained samples indicate dependences between polymer structure, composition and its properties.

Understanding the Fundamentals of Aqueous ATRP and Defining Conditions for Better Control

Conducting an atom transfer radical polymerization (ATRP) in water provides several intriguing challenges. In order to attain a deeper understanding of the mechanism of aqueous ATRP, with particular attention to the reasons for the potential loss of control, a systematic investigation was carried out with three copper-amine catalysts ([CuIIL]2+, L = PMDETA, TPMA and Me6TREN). The association constants (KX) of [CuIIL]2+ and [CuIL]+ with X– and OH–, as well as the relative stabilities and redox properties of the complexes, were determined as a function of both [X–] and pH. In addition, rate constants and equilibrium constants of disproportionation for all three [CuIL]+ complexes were measured. Finally, ATRP equilibrium constants (KATRP) were estimated for all complexes, using 2-hydroxyethyl 2-bromoisobutyrate (HEBiB) as initiator. The primary factors affecting control in aqueous ATRP were identified as catalyst instability at both low and high pH, easy dissociation of deactivator (KX < 15), very high KATRP and fast disproportionation of [CuIL]+. Overall, the results obtained in this study provide a set of guidelines for a well-controlled aqueous ATRP. The guidelines were used to conduct several efficient electrochemically mediated aqueous ATRP experiments with oligo(ethylene oxide) methyl ether methacrylate as monomer, HEBiB as initiator and copper complexes with three different ligands. A successful ATRP in a strongly acidic environment (pH 1.5) is reported for the first time, contrary to what was believed until now, indicating that ATRPs can be easily controlled in acidic conditions, while high pH should be avoided.

A Novel Janus Initiator for ATRP: Initiator Design and Application in Polymerization

A novel Janus compound containing azo‐based thermal initiator and bromo‐based atom transfer radical polymerization (ATRP) initiator group is synthesized. Such compound can be applied in the living radical polymerization of alkyl methacrylate monomers, such as methyl methacrylate, tert‐butyl methacrylate, and 2‐(N,N‐dimethylamino) ethyl methacrylate. Polymers with controlled molecular weights and narrow molecular weight distributions are obtained. The structure of polymers is identified by 1H NMR spectroscopy and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrum. A modified initiator for continuous activator regeneration ATRP mechanism is proposed according to the polymerization behavior, hydrolysis of chain backbone, and end group identification. image

AGET ATRP of Methyl Methacrylate Based on Thermoregulated Phase Transfer Catalysis in Organic/Aqueous Biphasic System: Facile and Highly Efficient In Situ Catalyst/Ligand Separation and Recycling

A novel polymerization system with activators generated by electron transfer for atom transfer radical polymerization (ATRP) for sustainable catalyst/ligand separation and recycling in situ is developed based on thermoregulated phase transfer catalysis in organic/aqueous biphasic system. Herein, a typical iniferter agent 1-cyano-1-methylethyldiethyldithiocarbamte is used as the initiator, and CuBr2, monomethoxy poly(ethylene glycol)-350-supported substituted dipicolylamine (L350), ascorbic acid, and methyl methacrylate are employed as the catalyst, thermoresponsive ligand, reducing agent, and the model monomer, respectively. The “living” nature of the system is confirmed by polymerization kinetics with recycled catalyst complex aqueous solution and chain-extension experiments via iniferter and ATRP mechanism, respectively. In addition, the catalyst residue in polymers is less than 2 ppm and the recycling efficiency of catalyst complex in water kept more than 95% even after 5 times of recovery experiments while keeping narrow molecular weight distribution (Mw/Mn < 1.33).

Synthesis and characterization of amphiphilic triblock Copolymers with Identical compositions but different block sequences

The amphiphilic triblock copolymers PAA-b-PS-b-PAA and PS-b-PAA-b-PS were synthesized by a combination of an atom transfer radical polymerization mechanism and a nitroxide radical coupling reaction or copper-catalyzed azide/alkyne click chemistry.

Modeling of the atom transfer radical polymerization for preparing novel fluorosilicone diblock copolymers in a semi‐batch reactor

ABSTRACTTo investigate the process for the preparation of well‐defined poly‐dimethylsiloxane‐b−2,2,3,3,4,4,4‐heptafluorobutylmetharylate block copolymers via a macroinitiator initiated atom transfer radical polymerization (ATRP), a model for the batch and semi‐batch ATRP process was presented based on the method of moments. The ATRP mechanism, the diffusion limitation, and the reactor choice were considered in the model. Besides, the polymer molecular weight, monomer conversion, and polymer polydispersity index as a function of polymerization time were described by this model. The model was validated by comparing simulated results with experimental data and was also used to investigate the effects of diffusion limitation and reactor choice (i.e., batch and semi‐batch reactors). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3473–3481, 2013

Synthesis of PMMA-b-PU-b-PMMA tri-block copolymers through ARGET ATRP in the presence of air

ARGET (activators regenerated by electron transfer) ATRP (atom transfer radical polymerization) has been suc- cessfully performed (in flasks fitted with rubber septa without the need for use of Schlenk line) in the presence of limited amount of air and with a very small (370 ppm) amount of copper catalyst together with an appropriate reducing agent Cu(0). Novelty of this work is that the poly(methyl methacrylate)-block-polyurethane-block-poly(methyl methacrylate) tri- block copolymers were synthesized for the first time through ARGET ATRP, by using tertiary bromine-terminated polyurethane as a macroinitiator (MBP-PU-MBP), CuBr2 or CuCl2 as a catalyst and N,N,N,N#,N#-pentamethyldiethylene- triamine (PMDETA) or 2,2-bipyridine (Bpy) as a complexing agent. As the polymerization time increases, both the monomer conversion and ln((M)0/(M)) increased and the molecular weight of copolymer increases linearly with increasing conversion. Theoretical number-average molecular weight (Mn, th) of the tri-block copolymers was found to be comparable with number-average molecular weight determined by GPC analyses (Mn, GPC). These results indicate that the formation of the tri-block copolymers was through atom transfer radical polymerization mechanism. 1 H and 13 C NMR spectral methods were employed to confirm chemical structures of synthesized macroinitiator and tri-block copolymers. Mole percentage of PMMA in the tri-block copolymers was calculated using 1 H NMR spectroscopy and was found to be comparable with the GPC results. Additionally, the studies of surface properties (confocal microscopy and SFE) of tri-block copolymer coatings confirmed the presence of MMA segments.

Atom transfer radical polymerization of hydrophilic monomers and its applications

Atom transfer radical polymerization (ATRP) has become one of the most widely used living radical polymerization techniques for preparation of polymers with pre-designed compositions, topologies and functionalities. Hydrophilic (co)polymers are broadly used in various fields, such as hybrid materials, surface modification and delivery carriers in biomedical areas because of their diverse functionalities and ideal characters, including their non-toxicity, biocompatibility and environmentally friendly nature. Polymerization of hydrophilic monomers by ATRP provides polymers with more colorful structures, as well as novel properties and extends the application scope of hydrophilic polymers due to its facile operation and commercially available catalysts, ligands and initiators of the methodology. This review focuses on ATRP of hydrophilic monomers, as well as its application as detailed in five aspects: (1) basic understanding of the ATRP mechanism and polymerization kinetics of hydrophilic monomers; (2) polymerization media for hydrophilic monomers; (3) topologies of polymers based on hydrophilic monomers; (4) polymerization by combination of ATRP with other techniques, and (5) applications of polymerization of hydrophilic monomers.

Application of Atom Transfer Radical Polymerization in Biosensing

Atom transfer radical polymerization (ATRP) is a novel class of signal amplification method. In polymerization process, monomers accumulate and grow up to form long-chain polymers with abundant electroactive or photoactive groups for coupling other molecules, resulting in the distinct increase of the loading of signal molecules and the detection sensitivity. This article reviewed the mechanism of ATRP, and summarized the recent applications of ATRP in biosensing. Particularly, future studies and prospects were envisioned.