Synergistic Effect of 1-Butyl-3-methylimidazolium Hexafluorophosphate and DMSO in the SARA ATRP at Room Temperature Affording Very Fast Reactions and Polymers with Very Low Dispersity

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

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

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

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

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

Liquid salts as eco-friendly solvents for atom transfer radical polymerization: a review

Liquid salts, comprising ionic liquids and eutectic mixtures, are organic compounds/mixtures characterized by a low melting point that have been emerging as a very promising eco-friendly solvent for atom transfer radical polymerization.

Externally controlled atom transfer radical polymerization

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

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.

Aqueous SARA ATRP using Inorganic Sulfites

Aqueous supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) using inorganic sulfites was successfully carried out for the first time. Under optimized conditions, a well-controlled poly[oligo(ethylene oxide) methyl ether acrylate] (POEOA) was obtained with <30 ppm of soluble copper catalyst using tris(2-pyridylmethyl)amine (TPMA) ligand in the presence of an excess of halide salts (e.g. NaCl). Inorganic sulfites (e.g. Na2S2O4) were continuously fed into the reaction mixture. The mechanistic studies proved that these salts can activate alkyl halides directly and regenerate the activator complex. The effects of the feeding rate of the SARA agent (inorganic sulfites), ligand and its concentration, halide salt and its concentration, sulfite used, and copper concentration, were systematically studied to afford fast polymerizations rates while maintaining the control over polymerization. The kinetic data showed linear first-order kinetics, linear evolution of molecular weights with conversion, and polymers with narrow molecular weight distributions (Đ ~1.2) during polymerization even at relatively high monomer conversions (~80%). "One-pot" chain extension and "one-pot" block copolymerization experiments proved the high chain-end functionality. The polymerization could be directly regulated by starting or stopping the continuous feeding of the SARA agent. Under biologically relevant conditions, the aqueous SARA ATRP using inorganic sulfites was used to synthesize a well-defined protein-polymer hybrid by grafting of P(OEOA480) from BSA-O-[iBBr]30.

Deep eutectic solvents for green and efficient iron-mediated ligand-free atom transfer radical polymerization

This article reports the iron-catalyzed ligand-free ATRP with DES as a green additive.

Cyclopentyl methyl ether as a green solvent for reversible-addition fragmentation chain transfer and nitroxide-mediated polymerizations

Cyclopentyl methyl ether (CPME) was successfully used as an environmentally friendly alternative to regularly employed organic solvents (e.g., THF, DMSO, DCM and DMF) for the RAFT and NMP polymerizations of vinyl chloride (VC) and styrene (S).

Recent Progress on Transition Metal Catalyst Separation and Recycling in ATRP

Atom transfer radical polymerization (ATRP) is a versatile and robust tool to synthesize a wide spectrum of monomers with various designable structures. However, it usually needs large amounts of transition metal as the catalyst to mediate the equilibrium between the dormant and propagating species. Unfortunately, the catalyst residue may contaminate or color the resultant polymers, which limits its application, especially in biomedical and electronic materials. How to efficiently and economically remove or reduce the catalyst residue from its products is a challenging and encouraging task. Herein, recent advances in catalyst separation and recycling are highlighted with a focus on (1) highly active ppm level transition metal or metal free catalyzed ATRP; (2) post-purification method; (3) various soluble, insoluble, immobilized/soluble, and reversible supported catalyst systems; and (4) liquid-liquid biphasic catalyzed systems, especially thermo-regulated catalysis systems.

Synthesis of functionalized poly(vinyl acetate) mediated by alkyne-terminated RAFT agents

Two new xanthates with alkyne functionalities were synthesized for the reversible addition fragmentation chain transfer (RAFT) polymerization of vinyl acetate (VAc).

Sulfolane: an Efficient and Universal Solvent for Copper-Mediated Atom Transfer Radical (co)Polymerization of Acrylates, Methacrylates, Styrene, and Vinyl Chloride

A very fast and controlled atom transfer radical (co)polymerization (ATRP) of acrylates, methacrylates, styrene, and vinyl chloride is reported in a single dipolar aprotic solvent, sulfolane, with the use of ppm amount of the copper catalyst. The observed rates of polymerization (k_p^app) of the monomers studied are similar to those reported using dimethyl sulfoxide (DMSO) and other polar solvents typically employed in single electron transfer (SET)-mediated atom transfer radical polymerization (ATRP) processes. As proof-of-concept, ABA type block copolymers of polystyrene-b-poly(vinyl chloride)-b-polystyrene and poly(methyl acrylate)-b-poly(vinyl chloride)-b-poly(methyl acrylate) were prepared for the first time using a reversible deactivation radical polymerization (RDRP) method in a single solvent. The quantitative preservation of halide chain-ends was confirmed by ¹H NMR and MALDI-TOF analysis as well as by the complete shift of the GPC traces. The results presented establish an innovative and robust system to afford a vast portfolio of (co)polymers in a single widely used industrial solvent.