Copper(I)-mediated living radical polymerization in the presence of oxyethylene groups: Online H-1 NMR spectroscopy to investigate solvent effects

摘要

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 H-1 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; M-n = 480) was carried out in toluene mediated by a copper(I) bromide/N-(n-propyl)-2-pyridylmethanimine catalyst, using phenyl alpha -bromoisobutyrate (1) as initiator. The measured number-average molar mass, M-n, of the product increases linearly with monomer conversion in close agreement to the theoretical M-n, 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 k(p)[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 I,2-diethoxyethane as solvent, which showed an enhanced rate when compared to polymerization in nonpolaroncoordinating solvents. The high value of k(p)[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. [References: 27]