Copper(I)‐mediated radical polymerization of methacrylates in aqueous solution

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Abstract
α‐Methoxypolyethylene oxide methacrylate was polymerized by copper(I)‐mediated living radical polymerization in aqueous solution to give polymers with controlled number‐average molecular masses and narrow polydispersities. When equimolar quantities of initiator with respect to copper(I) bromide were used, the reaction was extremely fast with quantitative conversion achieved in less than 5 min at ambient temperature. However, the molecular weight distribution was broad, and control over the number‐average molecular weight (Mn) growth was extremely poor; this is ascribed to an increase in termination because of the increased rate as a result of the coordination of water at the copper center. The complex formed between copper(I) bromide and N‐(n‐propyl)‐2‐pyridylmethanimine, bis[N‐(n‐propyl)‐2‐pyridylmethanimine]copper(I), was demonstrated to be stable in aqueous solution by 1H NMR over 10 h at 25 °C. However, on increasing the temperature to 50 °C, decomposition occurred rapidly. Thus, polymerization temperatures were maintained at ambient temperature. When longer alkyl chains were utilized in the ligand, that is, pentyl and octyl, the complex acted as a surfactant leading to heterogeneous solutions. When the catalyst concentration was reduced by two orders of magnitude, the rate of polymerization was reduced with 100% conversion achieved after 60 min with the Mn of the final product being higher than that predicted and the polydispersity equal to 1.43. Copper(II) was added as an inhibitor to circumvent these problems. When 10% of Cu(I) was replaced by Cu(II) {[Cu(I)] + [Cu(II)]/[I] = 1/100}, the mass distribution showed a bimodal distribution, and the rate of polymerization decreased significantly. With a catalyst composition [Cu(I)]/[Cu(II)] = 0.5/0.5 {[Cu(I)] + [Cu(II)]}/[I] = 1/100, polymerization proceeded slowly with 80% conversion reached after 22 h. Thus, the concentration of Cu(I) was further reduced with [Cu(I)]/[Cu(II)] = 10/90, {[Cu(I)] + [Cu(II)]}/[I] = 1/100. The system then contained [Initiator]/[Cu(I)] = 1000/1 and [I]/[Cu(II)] = 1000/9. Under these conditions, the reaction reached 50% after 5 h with the polymer having both an Mn close to the theoretical value and a narrow polydispersity of PDi = 1.15. Optimum results were obtained by increasing the amount of catalyst. When a ratio of [Cu(I)]/[Cu(II)] = 10/90 with a ratio of [Cu]/[I] = 1/1, a conversion of 100% was achieved after less than 20 h, leading to a product having Mn = 8500 and PDi = 1.15. Decreasing the amount of Cu(II) relative to Cu(I) to [Cu(I)]/[Cu(II)] = 0.5/0.5 (maintaining the overall amount of copper) led to 100% conversion after 75 min: Mn = 9500, PDi = 1.10. Block copolymers have been demonstrated by sequential monomer addition with excellent control over Mn and PDi. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1696–1707, 2001

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