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

Autor: Xiaosong Wang, Steven P. Armes, F. L. G. Malet, Sébastien Perrier, David M. Haddleton
Rok vydání: 2001
Předmět:
Zdroj: Journal of Polymer Science Part A: Polymer Chemistry. 39:1696-1707
ISSN: 1099-0518
0887-624X
Popis: 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 (M n ) 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 1 H 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 M n 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 M n 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 M n = 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 overal] amount of copper) led to 100% conversion after 75 min: M n = 9500, PDi = 1.10. Block copolymers have been demonstrated by sequential monomer addition with excellent control over M n and PDi.
Databáze: OpenAIRE
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