Single Electron Transfer-living Radical Polymerization Research Articles

Surface-Dependent Kinetics of Cu(0)-Wire-Catalyzed Single-Electron Transfer Living Radical Polymerization of Methyl Acrylate in DMSO at 25 °C

The effect of Cu(0) wire dimensions on the Cu(0) wire/Me6-TREN-catalyzed heterogeneous single-electron transfer living radical polymerization (SET-LRP) of methyl acrylate (MA) initiated with methyl 2-bromopropionate (MBP) in DMSO at 25 °C was analyzed by kinetic experiments. These kinetic results were compared with those of Cu(0) powder/Me6-TREN-catalyzed SET-LRP. Both wire and powder produce perfect SET-LRP with a first-order rate of polymerization in growing species up to 100% conversion. Nevertheless, Cu(0) wire experiments demonstrated SET-LRP with greater perfection, allowing for the accurate determination of the external rate order (vis-a-vis surface area) for heterogeneous Cu(0) catalyst and accurate prediction of kpapp from wire dimension. Cu(0) wire also exhibited a significantly greater control of molecular weight distribution than Cu(0) powder. The combined advantages of easier catalyst preparation, handling, predictability, tunability, simple recovery/recycling, and enhanced control of molecul...

PNIPAM‐b‐(PEA‐g‐PDMAEA) double‐hydrophilic graft copolymer: Synthesis and its application for preparation of gold nanoparticles in aqueous media

AbstractA series of well‐defined double‐hydrophilic graft copolymers, consisting of poly(N‐isopropylacrylamide)‐b‐poly(ethyl acrylate) (PNIPAM‐b‐PEA) backbone and poly(2‐(dimethylamino)ethyl acrylate) (PDMAEA) side chains, were synthesized by the combination of single‐electron‐transfer living radical polymerization (SET‐LRP) and atom‐transfer radical polymerization (ATRP). PNIPAM‐b‐PEA backbone was first prepared by sequential SET‐LRP of N‐isopropylacrylamide and 2‐hydroxyethyl acrylate at 25 °C using CuCl/tris(2‐(dimethylamino)ethyl)amine as catalytic system followed by the transformation into the macroinitiator by treating the pendant hydroxyls with 2‐chloropropionyl chloride. The final graft copolymers with narrow molecular weight distributions were synthesized by ATRP of 2‐(dimethylamino)ethyl acrylate initiated by the macroinitiator at 40 °C using CuCl/tris(2‐(dimethylamino)ethyl)amine as catalytic system via the grafting‐from strategy. These copolymers were employed to prepare stable colloidal gold nanoparticles with controlled size in aqueous solution without any external reducing agent. The morphology and size of the nanoparticles were affected by the length of PDMAEA side chains, pH value, and the feed ratio of the graft copolymer to HAuCl4. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1811–1824, 2009

A comparative analysis of SET‐LRP of MA in solvents mediating different degrees of disproportionation of Cu(I)Br

AbstractCu(I)Br/Me6‐TREN species are unstable and disproportionate into metallic Cu(0) and Cu(II)Br2/Me6‐TREN in DMSO, whereas in toluene are stable and do not undergo disproportionation, at least at 25 °C. To estimate the role of the disproportionating solvent in single electron‐transfer living radical polymerization (SET‐LRP) a comparative analysis of Cu(0)/Me6‐TREN‐catalyzed polymerization of MA initiated with methyl 2‐bromopropionate at 25 °C was performed in DMSO and toluene. A combination of kinetic experiments and chain end analysis by 500‐MHz 1H NMR spectroscopy was used to demonstrate that disproportionation represents the crucial requirement for a successful SET‐LRP of MA at 25 °C. In DMSO a perfect SET‐LRP occurs and yields close to 100% conversion in 45 min. A first order polymerization in growing species up to 100% conversion and a PMA with perfectly functional chain ends are obtained. However, in toluene within 17 h only about 60% conversion is obtained, the polymerization does not show first order in growing species and therefore is not a living polymerization. Moreover, at 60% conversion the resulting PMA has only 80% active chain ends. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6880–6895, 2008

Functionally terminated poly(methyl acrylate) by SET‐LRP initiated with CHBr3 and CHI3

AbstractThe single‐electron transfer living radical polymerization (SET‐LRP) of methyl acrylate initiated with bromoform (CHBr3) and iodoform (CHI3) and catalyzed by Cu(0)/Me6‐TREN in DMSO at 25 °C provides a reliable method to prepare poly (methyl acrylate) (PMA) with active chain ends and controlled structure that can undergo subsequent functionalization to provide strategies for the synthesis of different block copolymers and other complex architectures. A detailed kinetic and structural analysis was used to assess the scope and the limitations of CHBr3 and CHI3 as initiators under SET‐LRP conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 278–288, 2008

Role of Cu0 in Controlled/“Living” Radical Polymerization

Several propositions have been made about the mechanism in which Cu0 mediates controlled radical polymerization that include (1) exclusive activation of an alkyl halide initiator by exceptionally active Cu0 to generate a propagating radical and a CuI species, (2) instantaneous disproportionation of CuI into Cu0 and CuII in “catalytic” solvents such as DMSO, and (3) deactivation of the radical by CuII to establish an equilibrium between active and dormant polymer chains. It was further postulated that the activation and deactivation processes in this technique, entitled single-electron-transfer living radical polymerization (SET-LRP), occur via outer-sphere electron transfer (OSET) to produce alkyl halide radical anion intermediates. We report herein on our own investigation of the aforementioned mechanism using Cu complexes of tris[2-(dimethylamino)ethyl]amine (Me6TREN). Model studies were employed to quantify disproportionation of CuI/Me6TREN in DMSO, DMF, and MeCN, where comproportionation of Cu0 with CuII to form CuI was slow but dominant in all three solvents. Relative activation rates of alkyl halides by Cu0 and CuI with Me6TREN were studied; reactions catalyzed by CuI/Me6TREN were significantly faster than those employing Cu0. Polymerization of methyl acrylate proceeded in a similar manner in both DMSO and MeCN at 25 °C initiated by an alkyl halide using either Cu0 and Me6TREN, CuI/Me6TREN, or a slow dosing of CuI/Me6TREN. These studies ultimately indicate that in addition to slowly activating alkyl halides Cu0 also acts as a reducing agent, regenerating CuI activator from accumulated CuII, thereby emulating the mechanism activators regenerated by electron transfer in atom transfer radical polymerization (ARGET ATRP). The possibility of OSET among copper species and alkyl halides was evaluated on the basis of literature data and found to be negligible in comparison to an atom transfer process (i.e., inner-sphere electron transfer).

A density functional theory computational study of the role of ligand on the stability of CuI and CuII species associated with ATRP and SET‐LRP

AbstractAtom transfer radical polymerization (ATRP) and single electron‐transfer living radical polymerization (SET‐LRP) both utilize copper complexes of various oxidation states with N‐ligands to perform their respective activation and deactivation steps. Herein, we utilize DFT (B3YLP) methods to determine the preferred ligand‐binding geometries for Cu/N‐ligand complexes related to ATRP and SET‐LRP. We find that those ligands capable of achieving tetrahedral complexes with CuI and trigonal bipyramidal with axial halide complexes with [CuIIX]+ have higher energies of stabilization. We were able to correlate calculated preferential stabilization of [CuIIX]+ with those ligands that perform best in SET‐LRP. A crude calculation of energy of disproportionation revealed that the same preferential binding of [CuIIX]+ results in increased propensity for disproportionation. Finally, by examining the relative energies of the basic steps of ATRP and SET‐LRP, we were able to rationalize the transition from the ATRP mechanism to the SET‐LRP mechanism as we transition from typical nonpolar ATRP solvents to polar SET‐LRP solvents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4950–4964, 2007

Synthesis of perfectly bifunctional polyacrylates by single‐electron‐transfer living radical polymerization

AbstractPoly(methyl acrylate)s, poly(ethyl acrylate)s, and poly(butyl acrylate)s with α,ω‐di(bromo) chain ends and Mn from 8500 to 35,000 were synthesized by single‐electron‐transfer living radical polymerization (SET‐LRP). The analysis of their chain ends by a combination of 1H and 2D‐NMR, GPC, MALDI‐TOF MS, chain end functionalization, chain extension, and halogen exchange experiments demonstrated the synthesis of perfectly bifunctional polyacrylates by SET‐LRP. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4684–4695, 2007

Kinetic simulation of single electron transfer–living radical polymerization of methyl acrylate at 25 °C

AbstractA mechanistic comparison of the ATRP and SET‐LRP is presented. Subsequently, simulation of kinetic experiments demonstrated that, in the heterolytic outer‐sphere single‐electron transfer process responsible for the SET‐LRP, the activation of the initiator and of the propagating dormant species is faster than of the homolytic inner‐sphere electron‐transfer process responsible for ATRP. In addition, simulation experiments suggested that in both polymerizations the rate of deactivation is similar. In SET‐LRP, the Cu(II)X2/L deactivator is created by the disproportionation of Cu(I)X/L inactive species, while in ATRP its concentration is mediated by the bimolecular termination. The combination of higher rate of activation with the creation of deactivator via disproportionation provides, via SET‐LRP, an ultrafast synthesis of polymers with very narrow molecular weight distribution at room temperature. SET‐LRP is mediated by a catalytic amount of Cu(0), and under suitable conditions, bimolecular termination is virtually absent. Kinetic and simulation experiments have also demonstrated that the amount of water available in commercial solvents and monomers is sufficient to induce the disproportionation of Cu(I)X/L into Cu(0) and Cu(II)X2/L and, subsequently, to change the polymerization mechanism from ATRP to SET‐LRP. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1835–1847, 2007.