Mechanoacid polymer signals a smash hit

Abstract

A polymer that releases acid in response to a sharp blow can trigger “bruising” that reveals where and when it was struck (J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.9b12861). This kind of mechanochemistry—in which a mechanical force sets off a chemical reaction—could eventually lead to materials that offer an early warning signal of impending structural failure, for example. Polymer mechanochemistry relies on chemical groups called mechanophores, which undergo a chemical change when they are stretched or compressed. A team led by Stephen L. Craig and PhD student Yangju Lin of Duke University developed a new mechanophore, 2-methoxy-substituted gem-dichlorocyclopropane (MeO-gDCC), and incorporated it into polymer chains. Blasting the resulting molecules with ultrasound breaks a carbon-carbon bond in the cyclopropane ring to generate an allyl chloride intermediate, which in turn generates a chemical signal in the form of a pH change when it rearranges to release hydrogen chloride.“This chemistry addresses al...