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Copper(I)-Mediated Living Radical Polymerization in the Presence of Oxyethylene Groups:  Online 1H NMR Spectroscopy To Investigate Solvent Effects

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journal contribution
posted on 11.10.2000, 00:00 by David M. Haddleton, Sébastien Perrier, Stefan A. F. Bon
The use of oxyethylene methacrylate monomers, initiators, and 1,2-diethoxyethane as a cosolvent in the living radical polymerization mediated by copper(I) pyridylmethanimine complexes has been studied. Online 1H NMR monitoring of the reaction has been used to investigate the living radical polymerizations. Polymerization of poly(ethylene glycol) methyl ether methacrylate macromonomer (MeO(PEG)MA; Mn = 480) was carried out in toluene mediated by a copper(I) bromide/N-(n-propyl)-2-pyridylmethanimine catalyst, using phenyl α-bromoisobutyrate (1) as initiator. The measured number-average molar mass, Mn, of the product increases linearly with monomer conversion in close agreement to the theoretical Mn, with low polydispersity products (PDI < 1.2) achieved in all cases, as expected for a living polymerization. The overall rate of polymerization was very fast (ca. 90% conversion after 1 h at 90 °C) when compared to polymerization of benzyl methacrylate (BzMA) under similar conditions, indicating high values for kp[R*], where R* = active propagating species. The origin of this dramatic rate enhancement was investigated by carrying out the polymerization of MeO(PEG)MA over a range of temperatures and by the polymerization of alkyl methacrylates with a MeO(PEG)-derived macroinitiator. Polymerization of BzMA was carried out in 1,2-diethoxyethane as solvent, which showed an enhanced rate when compared to polymerization in nonpolar/noncoordinating solvents. The high value of kp[R*] is ascribed to complexation of the oxyethylene groups at the copper in a dynamic state with the pyridylmethanime ligand complexation, which results in a more active catalyst.