A Transiently Activated Rotaxane Mechanocatalyst

The activation of a latent catalyst by mechanical force, upon impact or fatigue for example, offers great promise for the creation of self-healing or stress-reporting polymer materials. Until now, such mechanocatalysts have relied on the scission of a covalent bond to generate the desired catalytic species, a process generally irreversible or difficult to control. Here, we report a transient [2]rotaxane mechanocatalyst featuring a thiourea active site, whose catalytic activity can be readily switched on by mechanical force, while spontaneously returning to an inactive state in the absence of force. In solution, the catalytic efficiency remains undiminished after 5 cycles, marking the first example of a recyclable mechanocatalyst. Benefiting from the low activation force threshold required to rupture noncovalent interactions, the catalytic efficiency in the solid state is comparable to that observed in solution. Moreover, it catalyzes the ring-opening polymerization of lactide in the solid state under simple compression without main chain degradation. Although the overall catalytic efficiency still needs further improvement, this new mechanocatalytic system shows its potential for the development of force-responsive materials.