A backbone lever-arm effect enhances polymer mechanochemistry

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. Polymer mechanochemistry can trigger a wide range of often unanticipated reactivity, but the focus of these systems typically falls on the structure of the mechanophore rather than the intervening polymer backbone. Now, it has been shown that a poly(norbornene) backbone has a substantial impact on a mechanochemical ring-opening reaction, despite having only a minor effect on the force-free reaction.

Cite this article

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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