Propagation and Chain-Length-Dependent Termination Rate Coefficients Deduced from a Single SP–PLP–EPR Experiment

Abstract

The laser single pulse (SP)–pulsed laser polymerization (PLP)–electron paramagnetic resonance (EPR) technique allows for deducing propagation (kp) and termination (kt) rate coefficients, including the chain-length dependence of kt, from a single pulsed-laser experiment. The method, which is particularly well suited for slowly terminating radicals, e.g., sterically hindered and ionic radicals, is illustrated for di(n-butyl) itaconate in bulk at temperatures from 30 to 60 °C. The time evolution of the DBI radical concentration is measured with a high time resolution at constant magnetic field. Propagation is associated with a relatively low pre-exponential A(kp), which is responsible for the small kp value of 6.8 L mol–1 s–1 at 30 °C. The chain-length dependence (CLD) of kt, deduced from the same SP–PLP–EPR signal as is kp, turns out to be adequately represented by the composite model. Whereas typical numbers are found for the power-law exponents for short and long radicals and for the crossover chain lengt...