Consistent experimental and theoretical evidence for long-lived intermediate radicals in living free radical polymerization

Feldermann, A., Coote, M. L., Stenzel, M. H., Davis, T. P., & Barner-Kowollik, C. (2004) Consistent experimental and theoretical evidence for long-lived intermediate radicals in living free radical polymerization. Journal of the American Chemical Society, 126(48).

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The cumyl dithiobenzoate (CDB)-mediated reversible addition fragmentation chain transfer (RAFT) polymerization of styrene at 30°C is studied via both kinetic experiments and high-level ab initio molecular orbital calculations. The kinetic data clearly indicate the delayed onset of steady-state behavior. Such an observation is consistent with the slow fragmentation model for the RAFT process, but cannot be reconciled with the cross-termination model. The comprehensive failure of the cross-termination model is quantitatively demonstrated in a detailed kinetic analysis, in which the independent influences of the pre-equilibria and main equilibria and the possible chain length dependence of cross-termination are fully taken into account. In contrast, the slow fragmentation model can describe the data, provided the main equilibrium has a large fragmentation constant of at least 8.9 × 106 L mol-1. Such a high equilibrium constant (for both equilibria) is consistent with high-level ab initio quantum chemical calculations (K = 7.3 × 106 L mol-1) and thus appears to be physically realistic. Given that the addition rate coefficient for macroradicals to (polymeric) RAFT agent is 4 × 106 L mol-1 s -1, this implies that the lifetime of the RAFT adduct radicals is close to 2.5 s. Since the radical is also kinetically stable to termination, it can thus function as a radical sink in its own right.

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ID Code: 99085
Item Type: Journal Article
Refereed: Yes
Additional Information: Cited By :143
Export Date: 5 September 2016
Correspondence Address: Coote, M.L.; Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia; email:
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Keywords: Polymerization, Polymers, Reaction kinetics, Cumyl dithiobenzoate (CDB), Macroradicals, Reversible addition fragmentation chain transfer (RAFT), Styrene, free radical, ab initio calculation, article, chemical reaction, molecular dynamics, reaction analysis, temperature sensitivity, theoretical study
ISSN: 00027863
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > Institutes > Institute for Future Environments
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Deposited On: 22 Sep 2016 04:50
Last Modified: 22 Sep 2016 04:50

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