To provide the scientific community involved in performing and modeling RAFT polymerizations with appropriate kinetic schemes as well as the best possible and critically evaluated kinetic parameters describing various RAFT processes.
The reversible addition fragmentation chain transfer (RAFT) polymerization has witnessed a rapid development during the last years. Although being widely used for the generation of both complex and well-defined polymeric materials – especially employing dithioester compounds as the mediating agents -, a complete understanding of the fundamental reaction scheme, which induces the equilibrium between dormant and active radical species, has not yet emerged. A deep understanding of the RAFT process, however, is mandatory to establish structure/rate correlations for a specific RAFT agent, which is essential for rational RAFT agent design delivering novel mediating compounds.
A wide variety of advanced techniques were applied in the near past to elucidate the detailed mechanism of RAFT polymerization and to arrive at rate coefficients describing the RAFT equilibrium reactions. It has been demonstrated that the choice of the reaction scheme operative in the RAFT process – with the inclusion of possible side-reactions – shows a major influence on the rate coefficients obtained by the experimental methods presently available. Significant experimental evidence has been put forward for the so-called slow fragmentation model (SFM) and the cross termination model (CTM), but alternative models such as reversible termination have also been discussed. Some of the disagreement in the literature may – however – stem from the fact that vastly differing reaction conditions have been employed in the individual studies.
The scope of the proposed project is to improve this obscure situation via jointly discussing the experimental evidence gathered by different scientific groups. The present proposal puts forward a program that brings together various research groups – who presently adhere to different mechanistic pictures – in order to put the scientific discussion on a common base. This task will be achieved via collating and comparing experimental results obtained for various RAFT systems. The current situation will be presented in a joint “dilemma-paper”, in which common agreement, but also outstanding inconsistencies, will be clarified in detail.
Subsequently, recommendations will be given how to rationally perform and present future kinetic RAFT experiments to guarantee comparability.
The final task of the project will be compiling and critically evaluating kinetic parameters for dithiobenzoate mediated RAFT polymerizations of styrenics, methacrylates and acrylates. Dithiobenzoates are the most widely used RAFT agents, both in synthetic work, due to their high reactivities, and in kinetic work, because of interesting rate altering effects. Reasonable kinetic parameters for these mediating agents are hence of priority to the scientific community.
This project is envisaged as first part of a series with subsequent parts considering kinetic data for additional monomer/RAFT agent systems.
Project announcement published in Chem. Int. Jul-Aug 2005.
The following publication constitutes the main outcome of this project:
Barner-Kowollik, C., Buback, M., Charleux, B., Coote, M. L., Drache, M., Fukuda, T., Goto, A., Klumperman, B., Lowe, A. B., Mcleary, J. B., Moad, G., Monteiro, M. J., Sanderson, R. D., Tonge, M. P. and Vana, P. (2006), Mechanism and kinetics of dithiobenzoate-mediated RAFT polymerization. I. The current situation. J. Polym. Sci. A Polym. Chem., 44: 5809-5831. https://dx.doi.org/10.1002/pola.21589
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