EPR and kinetic studies of atom transfer radical polymerization of (meth)acrylates

Electron paramagnetic resonance (EPR) spectroscopy and kinetic analysis were applied to atom transfer radical polymerization (ATRP) of (meth)acrylates. Although only copper(I) species was added to the system initially, EPR signals of copper(II) species were clearly observed in the polymerization mixture of methyl methacrylate (MMA) initiated by either ethyl 2-bromoisobutyrate (EBB) or p-toluenesulfonyl chloride (TsCl) in diphenyl ether. ATRP of methyl acrylate (MA) initiated by methyl 2-bromopropionate (MBP) in diphenyl ether also showed clear EPR signal of copper(II) species. As the polymerization proceeded, the concentration of copper(II) increased gradually until a nearly steady state was reached. The correlation between time dependence of concentration of copper(II) species and kinetics of polymerization is discussed for various ATRP systems. Our results indicate that conversion of 5-6% of initial copper(I) species to copper(I) species is observed for polymerization of MMA at 90 degrees C and ca. 3% conversion was found for MA.