RAFT/MADIX rate coefficients measured via time-resolved EPR spectroscopy after pulse laser initiation

Addition and fragmentation rate coefficients, kad and kβ, have been measured by individually tracing intermediate and propagating radical concentrations via highly time-resolved EPR spectroscopy after applying a laser single pulse. The method is illustrated for butyl acrylate polymerization at −40 °C with EDTCP (ethyl 2-[1-diethoxyphosphoryl-2,2,2-trifluoroethoxythio carbonylsulfanyl] propionate) being the MADIX agent. Analysis of the radical concentration vs. time profiles yields kad = (2.5 ± 0.1) × 104 L mol−1 s−1 and kβ = (2.3 ± 0.3) × 103 s−1. The associated Keq = kad/kβ value is in close agreement with Keq deduced from an earlier EPR method which rests on measuring the ratio of intermediate and propagating radical concentrations during stationary polymerization.