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Title: | Direct Access to Dithiobenzoate RAFT Agent Fragmentation Rate Coefficients by ESR Spin-Trapping | Authors: | RANIERI, Kayte Delaittre, Guillaume Barner-Kowollik, Christopher JUNKERS, Tanja |
Issue Date: | 2014 | Publisher: | WILEY-V C H VERLAG GMBH | Source: | MACROMOLECULAR RAPID COMMUNICATIONS, 35 (23), p. 2023-2028 | Abstract: | The beta-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 degrees 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 E-A = 82 +/- 13.3 kJ mol(-1) and A = (1.4 +/- 0.25) x 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 polymerization, 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. | Notes: | [Ranieri, Kayte; Junkers, Thomas] Hasselt Univ, Inst Mat Res IMO, Polymer React Design Grp, B-3590 Diepenbeek, Belgium. [Delaittre, Guillaume; Barner-Kowollik, Christopher] Karlsruhe Inst Technol, Inst Tech Chem & Polymerchem, D-76128 Karlsruhe, Germany. [Delaittre, Guillaume] Karlsruhe Inst Technol, Inst Toxicol & Genet, D-76344 Karlsruhe, Germany. [Barner-Kowollik, Christopher] Karlsruhe Inst Technol, Inst Biol Grenzflachen, D-76344 Eggenstein Leopoldshafen, Germany. [Junkers, Thomas] IMEC, Div IMOMEC, B-3590 Diepenbeek, Belgium. | Keywords: | electron spin resonance; fragmentation rate; kinetics; polymer reactions; reversible addition-fragmentation chain transfer; spin-trapping;electron spin resonance; fragmentation rate; kinetics; polymer reactions; reversible addition–fragmentation chain transfer; spin-trapping | Document URI: | http://hdl.handle.net/1942/18129 | ISSN: | 1022-1336 | e-ISSN: | 1521-3927 | DOI: | 10.1002/marc.201400518 | ISI #: | 000345977300007 | Rights: | © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. | Category: | A1 | Type: | Journal Contribution | Validations: | ecoom 2016 |
Appears in Collections: | Research publications |
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