The mechanical degradation of polymers is typically limited to a single chain scission per triggering chain stretching event and the loss of stress transfer that results from the scission limits the extent of degradation that can be achieved. Here we report a mechanically triggered delayed scission strategy that allows many eventual scission events to be initiated within a single polymer chain. The strategy is demonstrated via a mechanophore with a [4.2.0]bicyclooctene (BCOE) core that leverages a mechanochemical orbital symmetry-forbidden 4-electron disrotatory ring-opening reaction to set up a subsequent force-free and thermodynamically favorable lactonization. Ultrasonication of a 120 kDa BCOE copolymer triggers the desired mechanical remodeling of the polymer backbone and the resulting lactonization leads to a gradual decrease in molecular weight over the course of 9 days to a final value of 4.4 kDa more than an order of magnitude smaller than control polymers in which the ring-opened BCOE is protected from lactonizing. The force-coupled activity of the ring-opening reaction is probed by single molecule force spectroscopy and through the use of internal standards in sonication and the forces required for activation are far smaller than is typically required for the mechanical chain scission of conventional covalent polymers.
