Barth, J.; Buback, M.; Hesse, P.; Sergeeva, T.
EPR Analysis of n-Butyl Acrylate Radical Polymerization
Macromol. Rapid Commun. 2009, 30, 1969-1974.

Via electron paramagnetic resonance (EPR) spectroscopy, concentrations of secondary propagating radicals (SPRs) and tertiary mid-chain radicals (MCRs) in n-butyl acrylate solution polymerization were measured. The EPR spectrum is dominated by the 4-line spectrum of SPRs at −50 °C and by the 7-line spectrum of MCRs at +70 °C. At intermediate temperatures, a third spectral component is seen, which is assigned to an MCR species with restricted rotational mobility. The MCR components are produced by 1,5-hydrogen shift (backbiting) of SPRs. The measured ratio of MCRs to SPRs allows for estimating the rate coefficient k_p^t for monomer addition to a mid-chain radical. For 70 °C, k_p^t is obtained to be 65.5 L · mol⁻¹ · s⁻¹.