title: Direct access to dithiobenzoate RAFT agent fragmentation rate coefficients by ESR spin-trapping.
abstract: The β-scission rate coefficient of tert-butyl radicals fragmenting off the intermediate resulting from their addition to tert-butyl dithiobenzoate-a reversible addition-fragmentation chain transfer (RAFT) agent-is estimated via the recently introduced electron spin resonance (ESR)-trapping methodology as a function of temperature. The newly introduced ESR-trapping methodology is critically evaluated and found to be reliable. At 20 °C, a fragmentation rate coefficient of close to 0.042 s(-1) is observed, whereas the activation parameters for the fragmentation reaction-determined for the first time-read EA = 82 ± 13.3 kJ mol(-1) and A = (1.4 ± 0.25) × 10(13) s(-1) . The ESR spin-trapping methodology thus efficiently probes the stability of the RAFT adduct radical under conditions relevant for the pre-equilibrium of the RAFT process. It particularly indicates that stable RAFT adduct radicals are indeed formed in early stages of the RAFT poly-merization, at least when dithiobenzoates are employed as controlling agents as stipulated by the so-called slow fragmentation theory. By design of the methodology, the obtained fragmentation rate coefficients represent an upper limit. The ESR spin-trapping methodology is thus seen as a suitable tool for evaluating the fragmentation rate coefficients of a wide range of RAFT adduct radicals.
authors.affiliation: Polymer Reaction Design Group, Institute for Materials Research (IMO), Hasselt University, Campus Diepenbeek, Building D, B-3590, Diepenbeek, Belgium.
authors.forename: Kayte
authors.initials: K
authors.lastname: Ranieri
authors.forename: Guillaume
authors.initials: G
authors.lastname: Delaittre
authors.forename: Christopher
authors.initials: C
authors.lastname: Barner-Kowollik
authors.forename: Thomas
authors.initials: T
authors.lastname: Junkers
mesh_terms: D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D011108:Polymers / Q000737:chemistry
chemical_list: D011108:Polymers
keywords: electron spin resonance; fragmentation rate; kinetics; polymer reactions; reversible addition-fragmentation chain transfer; spin-trapping