Quantitative Connection between Macroscopic Stress and Bond-Breaking Force Enabled by Time-Stamped Mechanochemical Fluorescence

Mechanical stress is ubiquitous in materials, and it is well accepted that stress causes material wear and failure—which, at the molecular level, results from force-induced bond breakage. Understanding the mechanical behavior of materials at the molecular level requires a quantitative relationship between macroscopic stress and bond-breaking force, a connection that remains largely unexplored. Here we report that the macroscopic stress and the bond-breaking force are quantitatively connected through the kinetics of mechanically activated retro-Diels–Alder reaction of an anthracene–maleimide adduct mechanophore, which is embedded within the crosslink of a double-network elastomer. We find that the force required for bond breakage is largely insensitive to the strain applied to the elastomer but increases linearly with the logarithm of the strain rate. These findings provide insights into the mechanical behavior of polymeric materials and offer valuable guidance for the design of mechanically responsive materials.