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Mechanochemical strengthening of a synthetic polymer in response to typically destructive shear forces


High shear stresses are known to trigger destructive bond-scission reactions in polymers. Recent work has shown that the same shear forces can be used to accelerate non-destructive reactions in mechanophores along polymer backbones, and it is demonstrated here that such mechanochemical reactions can be used to strengthen a polymer subjected to otherwise destructive shear forces. Polybutadiene was functionalized with dibromocyclopropane mechanophores, whose mechanical activation generates allylic bromides that are crosslinked in situ by nucleophilic substitution reactions with carboxylates. The crosslinking is activated efficiently by shear forces both in solvated systems and in bulk materials, and the resulting covalent polymer networks possess moduli that are orders-of-magnitude greater than those of the unactivated polymers. These molecular-level responses and their impact on polymer properties have implications for the design of materials that, like biological materials, actively remodel locally as a function of their physical environment.

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Figure 1: The mechanochemical self-strengthening concept.
Figure 2: Shear-induced mechanochemical crosslinking in solution and the bulk.
Figure 3: Chemistry and response of a single-component ARM system.


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This material is based on work supported by the US Army Research Laboratory and the Army Research Office under Grant W911NF-07-1-0409 and the National Science Foundation (DMR-1122483). A.L.B.R. was supported by a Department of Defense Science, Mathematics and Research for Transformation Fellowship and Z.S.K. by a National Institutes of Health NIGMS Biotechnology Predoctoral Training Grant (T32GM8555).

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A.L.B.R. and S.L.C. conceived and designed the experiments. A.L.B.R. and Z.S.K. performed the synthesis, J.A.O. contributed extrusion equipment and analysed that data with A.L.B.R. A.L.B.R. and S.M.E. performed the shear experiments. W.E.K. contributed the nanoindentation tools and M.C. performed the nanoindentation experiments and analysed that data. A.L.B.R., Z.S.K. and S.L C. analysed the data and co-wrote the paper.

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Correspondence to Stephen L. Craig.

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Ramirez, A., Kean, Z., Orlicki, J. et al. Mechanochemical strengthening of a synthetic polymer in response to typically destructive shear forces. Nature Chem 5, 757–761 (2013).

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