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

2013; Nature Portfolio; Volume: 5; Issue: 9 Linguagem: Inglês

10.1038/nchem.1720

1755-4349

Ashley L. Black Ramirez, Zachary S. Kean, Joshua A. Orlicki, Mangesh Chandrashekhar Champhekar, Sarah M. Elsakr, Wendy E. Krause, Stephen L. Craig,

Mechanical and Optical Resonators

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. Materials typically break down in response to the repeated mechanical forces that they experience during use. Now, it has been shown that a mechanochemically active polymer can respond to shear forces by forming more bonds than are broken, leading to improved mechanical properties under conditions that would otherwise be destructive.