EPR study of the atom transfer radical polymerization (ATRP) of (meth)acrylates

Electron paramagnetic resonance (EPR) spectroscopy was applied to atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and methyl acrylate (MA) in order to investigate the mechanism of the controlled/“living” radical polymerization system. Although initially only copper(I) species was added to the system as a catalyst, EPR signals of copper(II) species were observed during the polymerization of MMA initiated by ethyl 2-bromoisobutyrate and p-methylbenzenesulfonyl chloride, and polymerization of MA initiated by methyl 2-bromopropionate. As the polymerization proceeded, the concentration of copper(II) increased gradually until a steady state was reached. The EPR results indicate that 5–6% of copper(I) species converted to copper(II) species in polymerization of MMA and about 3% in polymerization of MA at 90°C.