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      Mechanism of supplemental activator and reducing agent atom transfer radical polymerization mediated by inorganic sulfites: experimental measurements and kinetic simulations

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          The mechanism of ATRP mediated by Na 2S 2O 4, with Cu IIBr 2/Me 6TREN as the catalyst in ethanol/water mixtures, was investigated experimentally and by kinetic simulations.


          The mechanism of atom transfer radical polymerization (ATRP) mediated by sodium dithionite (Na 2S 2O 4), with Cu IIBr 2/Me 6TREN as catalyst (Me 6TREN: 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 SO 2˙ radical anion derived from Na 2S 2O 4, acting as both supplemental activator (SA) of alkyl halides and reducing agent (RA) for Cu II/L to regenerate the main activator Cu I/L. This is similar to the reversible-deactivation radical polymerization (RDRP) procedure conducted in the presence of Cu 0. The electron transfer from SO 2˙ , to either Cu IIBr 2/Me 6TREN 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 Cu IIBr 2/Me 6TREN and solubility of Na 2S 2O 4 on the level of polymerization control. The presence of small amounts of water in the polymerization mixtures slightly increased the reactivity of the Cu I/L complex, but markedly increased the reactivity of sulfites.

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          Atom Transfer Radical Polymerization (ATRP): Current Status and Future Perspectives

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            Ultrafast synthesis of ultrahigh molar mass polymers by metal-catalyzed living radical polymerization of acrylates, methacrylates, and vinyl chloride mediated by SET at 25 degrees C.

            Conventional metal-catalyzed organic radical reactions and living radical polymerizations (LRP) performed in nonpolar solvents, including atom-transfer radical polymerization (ATRP), proceed by an inner-sphere electron-transfer mechanism. One catalytic system frequently used in these polymerizations is based on Cu(I)X species and N-containing ligands. Here, it is reported that polar solvents such as H(2)O, alcohols, dipolar aprotic solvents, ethylene and propylene carbonate, and ionic liquids instantaneously disproportionate Cu(I)X into Cu(0) and Cu(II)X(2) species in the presence of a diversity of N-containing ligands. This disproportionation facilitates an ultrafast LRP in which the free radicals are generated by the nascent and extremely reactive Cu(0) atomic species, while their deactivation is mediated by the nascent Cu(II)X(2) species. Both steps proceed by a low activation energy outer-sphere single-electron-transfer (SET) mechanism. The resulting SET-LRP process is activated by a catalytic amount of the electron-donor Cu(0), Cu(2)Se, Cu(2)Te, Cu(2)S, or Cu(2)O species, not by Cu(I)X. This process provides, at room temperature and below, an ultrafast synthesis of ultrahigh molecular weight polymers from functional monomers containing electron-withdrawing groups such as acrylates, methacrylates, and vinyl chloride, initiated with alkyl halides, sulfonyl halides, and N-halides.
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              Metal-free atom transfer radical polymerization.

              Overcoming the challenge of metal contamination in traditional ATRP systems, a metal-free ATRP process, mediated by light and catalyzed by an organic-based photoredox catalyst, is reported. Polymerization of vinyl monomers are efficiently activated and deactivated with light leading to excellent control over the molecular weight, polydispersity, and chain ends of the resulting polymers. Significantly, block copolymer formation was facile and could be combined with other controlled radical processes leading to structural and synthetic versatility. We believe that these new organic-based photoredox catalysts will enable new applications for controlled radical polymerizations and also be of further value in both small molecule and polymer chemistry.

                Author and article information

                Polymer Chemistry
                Polym. Chem.
                Royal Society of Chemistry (RSC)
                : 8
                : 42
                : 6506-6519
                [1 ]Department of Chemistry
                [2 ]Carnegie Mellon University
                [3 ]Pittsburgh
                [4 ]USA
                [5 ]CEMMPRE
                [6 ]Department of Chemical Engineering
                [7 ]University of Coimbra
                [8 ]3030-790 Coimbra
                [9 ]Portugal
                [10 ]CIEPQPF
                [11 ]Faculty of Sciences and Technology
                © 2017


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