Ultrafast and Reversible Multiblock Formation by the SET-Nitroxide Radical Coupling Reaction

Jakov Kulis; Craig A. Bell; Aaron S. Micallef; Michael J. Monteiro

doi:10.1071/CH10092

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Ultrafast and Reversible Multiblock Formation by the SET-Nitroxide Radical Coupling Reaction

Jakov Kulis ^A , Craig A. Bell ^A , Aaron S. Micallef ^A and Michael J. Monteiro ^A ^B

+ Author Affiliations

- Author Affiliations

^A Australian Institute for Bioengineering and Nanotechnology, University of Queensland, Brisbane, Qld 4072, Australia.

^B Corresponding author. Email: m.monteiro@uq.edu.au

Australian Journal of Chemistry 63(8) 1227-1236 https://doi.org/10.1071/CH10092
Submitted: 18 February 2010 Accepted: 17 May 2010 Published: 10 August 2010

Abstract

The single electron transfer-nitroxide radical coupling (SET-NRC) reaction has been used to produce multiblock polymers with high molecular weights in under 3 min at 50°C by coupling a difunctional telechelic polystyrene (Br-PSTY-Br) with a dinitroxide. The well known combination of dimethyl sulfoxide as solvent and Me₆TREN as ligand facilitated the in situ disproportionation of Cu^IBr to the highly active nascent Cu⁰ species. This SET reaction allowed polymeric radicals to be rapidly formed from their corresponding halide end-groups. Trapping of these carbon-centred radicals at close to diffusion controlled rates by dinitroxides resulted in high-molecular-weight multiblock polymers. Our results showed that the disproportionation of Cu^I was critical in obtaining these ultrafast reactions, and confirmed that activation was primarily through Cu⁰. We took advantage of the reversibility of the NRC reaction at elevated temperatures to decouple the multiblock back to the original PSTY building block through capping the chain-ends with mono-functional nitroxides. These alkoxyamine end-groups were further exchanged with an alkyne mono-functional nitroxide (TEMPO–≡) and ‘clicked’ by a Cu^I-catalyzed azide/alkyne cycloaddition (CuAAC) reaction with N₃–PSTY–N₃ to reform the multiblocks. This final ‘click’ reaction, even after the consecutive decoupling and nitroxide-exchange reactions, still produced high-molecular-weight multiblocks efficiently. These SET-NRC reactions would have ideal applications in re-usable plastics and possibly as self-healing materials.

Acknowledgements

J.K. thanks the RACI Polymer Division for the Sir Ted Treloar Prize received at PPC11 in Cairns. M.J.M. acknowledges financial support from an ARC Discovery Projects (DP0987315) and receipt of an ARC Future Fellowship.

References

Ultrafast and Reversible Multiblock Formation by the SET-Nitroxide Radical Coupling Reaction

Abstract

Acknowledgements

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