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 1 H 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)-2pyridylmethanimine catalyst, using phenyl R-bromoisobutyrate (1) as initiator. The measured numberaverage 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 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.