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A backbone lever-arm effect enhances polymer mechanochemistry

Nature Chemistry volume 5, pages 110–114 (2013)Cite this article

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Abstract

Mechanical forces along a polymer backbone can be used to bring about remarkable reactivity in embedded mechanically active functional groups, but little attention has been paid to how a given polymer backbone delivers that force to the reactant. Here, single-molecule force spectroscopy was used to directly quantify and compare the forces associated with the ring opening of gem-dibromo and gem-dichlorocyclopropanes affixed along the backbone of cis-polynorbornene and cis-polybutadiene. The critical force for isomerization drops by about one-third in the polynorbornene scaffold relative to polybutadiene. The root of the effect lies in more efficient chemomechanical coupling through the polynorbornene backbone, which acts as a phenomenological lever with greater mechanical advantage than polybutadiene. The experimental results are supported computationally and provide the foundation for a new strategy by which to engineer mechanochemical reactivity.

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Figure 1: Structure of gDHC functionalized polymers used in this work.
Figure 2: Representative force–extension curves showing that the plateau force is more sensitive to the polymer backbone (a versus c and b versus d) than to the halogen (a versus b and c versus d).
Figure 3: Plots of measured polymer extensions versus fractional gDHC content, showing that the extensions are due to the reactivity of the gDHC mechanophores.
Figure 4: Calculated distortion of the local reaction coordinate (C–C distance) d in a polymer triad as a function of applied force for different polymer backbones.

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Acknowledgements

This material is based on work supported by the US Army Research Laboratory and the Army Research Office (grant no. W911NF-07-1-0409) and the National Science Foundation (DMR-1122483). The authors thank B. Akhremitchev for providing the original force–extension modelling code.

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Author notes

  1. Hope M. Klukovich and Tatiana B. Kouznetsova: These authors contributed equally to this work

Authors and Affiliations

  1. Department of Chemistry, Duke University, Durham, 27708, North Carolina, USA

    Hope M. Klukovich, Tatiana B. Kouznetsova, Zachary S. Kean, Jeremy M. Lenhardt & Stephen L. Craig

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  1. Hope M. Klukovich
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Contributions

H.M.K and S.L.C. conceived and designed the experiments. H.M.K. and J.M.L. performed the synthesis. T.B.K. collected the AFM data. H.M.K., T.B.K. and S.L.C. analysed the data. Z.S.K. contributed modelling data. H.M.K. and S.L.C. wrote the manuscript.

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Correspondence to Stephen L. Craig.

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Klukovich, H., Kouznetsova, T., Kean, Z. et al. A backbone lever-arm effect enhances polymer mechanochemistry. Nature Chem 5, 110–114 (2013). https://doi.org/10.1038/nchem.1540

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