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

Electron paramagnetic resonance (EPR) spectroscopy and kinetic analysis wer e applied to atom transfer radical polymerization (ATRP) of (meth)acrylates . Although only copper(I) species was added to the system initially, EPR si gnals of copper(II) species were clearly observed in the polymerization mix ture of methyl methacrylate (MMA) initiated by either ethyl 2-bromoisobutyr ate (EBB) or p-toluenesulfonyl chloride (TsCl) in diphenyl ether. ATRP of m ethyl acrylate (MA) initiated by methyl 2-bromopropionate (MBP) in diphenyl ether also showed clear EPR signal of copper(II) species. As the polymeriz ation 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 di scussed for various ATRP systems. Our results indicate that conversion of 5 -6% of initial copper(I) species to copper(I) species is observed for polym erization of MMA at 90 degrees C and ca. 3% conversion was found for MA.