Photoinduced metal-free atom transfer radical polymerization (ATRP) of methyl methacrylate was investigated using several phenothiazine derivatives and other related compounds as photoredox catalysts. The experiments show that all selected catalysts can be involved in the activation step, but not all of them participated efficiently in the deactivation step. The redox properties and the stability of radical cations derived from the catalysts were evaluated by cyclic voltammetry. Laser flash photolysis (LFP) was used to determine the lifetime and activity of photoexcited catalysts. Kinetic analysis of the activation reaction according to dissociative electron-transfer (DET) theory suggests that the activation occurs only with an excited state of catalyst. Density functional theory (DFT) calculations revealed the structures and stabilities of the radical cation intermediates as well as the reaction energy profiles of deactivation pathways with different photoredox catalysts. Both experiments and calculation...

Mechanism of Photoinduced Metal-Free Atom Transfer Radical Polymerization: Experimental and Computational Studies.

Electrochemically mediated atom transfer radical polymerization (eATRP)

Kinetics of Atom Transfer Radical Polymerization

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.

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

Lithium sulfur battery (LSB) research has received considerable attention due to the high theoretical gravimetric energy density of LSBs. However, in practice, the active sulfur material needs to be coupled with a conducting material due to its poor electronic conductivity (5 × 10−30 S cm−1) – reducing the battery energy density. Furthermore, lithium polysulfides (PSs), formed as soluble intermediate phases, can shuttle between the cathode and the anode – leading to rapid capacity degradation. Coating the traditional separators is one way to mitigate the shuttle effect which requires proper understanding of the nature of PSs to design effective separator coating materials. In this review, the technical limitations of LSBs are introduced with detailed information about the PS dimensions. Subsequently, carbon, polymer and inorganic coating materials have been highlighted with their significant contributions to the performance of LSBs. A particular focus has been placed on their mechanisms of trapping PSs through polar–polar, Lewis acid–base interactions and physical confinement. Finally, the key factors which influence the performances of LSBs are summarized.

Recent advances in separators to mitigate technical challenges associated with re-chargeable lithium sulfur batteries

SET-LRP of NIPAM in water via in situ reduction of Cu(II) to Cu(0) with NaBH4

Copper complexes bearing polyamine chelate ligands are among the most widely used and highly active catalysts for atom transfer radical polymerization (ATRP). Copper(I) complexes of these ligands (CuIL) react with an alkyl halide initiator (RX) in the atom transfer step to generate the higher oxidation state halido complex CuIILX and the radical R•. However, CuIL present in the reaction also has the potential to react with the liberated radicals to generate the organometallic species CuIILR (where R is formally a carbanion). The reversible association of radical and CuIL would facilitate the operation of an alternate, competitive controlled radical polymerization pathway known as organometallic-mediated radical polymerization (OMRP). Recently this possibility has been proposed to occur for a number of different copper catalysts under ATRP conditions, but unequivocal evidence of this organometallic adduct is lacking. Herein we provide direct observation of this species, including an optical spectrum for tw...

Organo-Copper(II) Complexes as Products of Radical Atom Transfer.

Copper polyamine complexes are among the most utilized catalysts for controlled radical polymerization reactions Copper(I) complexes may react reversibly with an alkyl halide to form an alkyl radical, which promotes polymerization, and a copper(II) halido complex in a step known as activation The kinetics of the reverse reaction between the alkyl radical and higher oxidation-state copper complex (deactivation) are less studied because these reactions approach diffusion-controlled rates, and it is difficult to isolate or quantify the concentration of the alkyl radical (R•) in situ Herein we report a broadly applicable electrochemical technique for simultaneously measuring the kinetics of deactivation and kinetics of activation

New method for exploring deactivation kinetics in copper-catalyzed atom-transfer-radical reactions.

Atom transfer radical addition (ATRA) and polymerisation (ATRP) reactions are commonly catalyzed by copper(I) complexes which react, reversibly, with a dormant alkyl halide initiator (RX) releasing a reactive organic radical R˙. The copper catalyst bears a multidentate N-donor ligand (L) and the active catalyst is simply CuIL. The role of the catalyst in these reactions is to abstract a halogen atom from RX forming the corresponding higher oxidation state species CuIILX. However, in order to perform its catalytic function (in multiple turnovers) the halido ligand must be released from the copper ion en route to regenerating the active catalyst CuIL. In this work we investigate the kinetics of the CuILX/CuIL equilibrium where L is the tridentate N,N,N′,N′′,N′′-pentamethyl-diethylenetriamine (PMDETA). Using electrochemical analysis we find that the rate of formation of the active catalyst CuIL is strongly dependent on solvent. We demonstrate that both the kinetics and thermodynamics of this simple ligand exchange reaction are critical in the overall reaction pathway.

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Timothy J. Zerk

Papers

SET-LRP of NIPAM in water via in situ reduction of Cu(II) to Cu(0) with NaBH4

Organo-Copper(II) Complexes as Products of Radical Atom Transfer.

New method for exploring deactivation kinetics in copper-catalyzed atom-transfer-radical reactions.

Solvent dependent anion dissociation limits copper(I) catalysed atom transfer reactions

Redox-coupled structural changes in copper chemistry: Implications for atom transfer catalysis