In order to assess the role of the solvent mediating the disproportionation of Cu(I)X into Cu(0) and Cu(II)X 2 during SET-LRP, a series of polymerizations of methyl acrylate initiated with methyl 2-bromopropionate and catalyzed by Cu(0)/Me 6 -TREN at 25 °C in DMSO, MeCN, and their mixtures were investigated. These polymerizations proceed in a dissimilar manner. SET-LRP of MA in DMSO, a solvent that mediates disproportionation, was exemplary of "ultrafast living radical polymerization" with complete conversion in 45 min following the expected first-order kinetics and providing perfect fidelity of the structure of the polymer chain ends. When the polymerization was performed in MeCN, a solvent in which Cu(I)X species do not disproportionate, it displayed nonlinear first-order kinetics with a poor retention of the bromine chain end functionality. The lack of first-order kinetics and decrease of chain end functionality with conversion indicate a nonliving polymerization in MeCN. Increasing the concentration of DMSO in DMSO/MeCN mixtures provided a continuous transition from a nonliving to a living polymerization. The incompatibility of MeCN with SET-LRP lends support that disproportionation of Cu(I)X/N ligand to Cu(0) and Cu(II)X 2 /N ligand is the key step in SET-LRP.

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The effect of Cu(0) wire dimensions on the Cu(0) wire/Me 6 -TREN-catalyzed heterogeneous singleelectron 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/Me 6 -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 k p app 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 molecular weight distribution make Cu(0)-wire-catalyzed SET-LRP the ideal methodology for the synthesis of tailored polyacrylates.

In order to estimate the effect of Cu(0) particle size in SET-LRP, a comparative analysis of Cu(0)/ Me 6 -TREN-catalyzed polymerization of MA initiated with methyl 2-bromopropionate at 25 °C was performed in DMSO, a solvent that mediates the disproportionation of Cu(I)X, and in MeCN, a solvent in which Cu(I)X does not disproportionate Cu(I)X. Decreasing the Cu(0) particle size results in a marked increase in the apparent rate constant of propagation (k p app ). Decreasing the Cu(0) particle size from 425 to 0.05 µm (50 nm) increases the k p app by almost an order of magnitude. Regardless of the Cu(0) particle size used, in DMSO a perfect SET-LRP occurs with a first-order polymerization in growing species up to 100% conversion. However, in MeCN the polymerization is not first order in growing species. The results presented here demonstrate that, in addition to the disproportionation of Cu(I)X/L into Cu(0) and Cu(II)X 2 /L, the particle size of Cu(0) plays a strong role in the kinetics during the entire polymerization.

Alcohols are known to promote the disproportionation of Cu(I)X species into nascent Cu(0) and Cu(II)X. Therefore, alcohols are expected to be excellent solvents that facilitate the single‐electron transfer mediated living radical polymerization (SET‐LRP) mediated by nascent Cu(0) species. This publication demonstrates the ultrafast SET‐LRP of methyl acrylate initiated with bis(2‐bromopropionyloxy)ethane and catalyzed by Cu(0)/Me6‐TREN in methanol, ethanol, 1‐propanol, and tert‐butanol and in their mixture with water at 25 °C. The structural analysis of the resulting polymers by a combination of 1H NMR and MALDI‐TOF MS demonstrates the synthesis of perfectly bifunctional α,ω‐dibromo poly(methyl acrylate)s by SET‐LRP in alcohols. Moreover, this work provides an expansion of the list of solvents available for SET‐LRP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2745–2754, 2008