Mechanochemical Unzipping and Force-Free Rezipping of Poly(endo-tricyclodecadiene) via Cascade Radical Reactivity.

Polymer mechanochemistry typically concerns the transformation of isolated mechanophores upon application of force. We recently reported a polymer in which electronic coupling between repeat units allows continuous segments of mechanophores to undergo cascade reactivity and transform the polymer backbone, while isolating repeat units from each other shuts down the mechanochemical reactivity. Here, we show that this reactivity can be generalized to a class of common ROMP polymers, poly(endo-tricyclodecadiene)s. Subjecting these polymers to mechanical force induces radical cascade reactivity along the backbone, leading to unzipping of the repeat units to transform the backbone structure. Furthermore, significant ring strain is not present in this scaffold. Therefore, chemically generating radicals on the mechanochemically transformed polymer backbone in the absence of force enables reversion to the original structure. This work demonstrates a new design paradigm for reversible polymer backbone transformation under orthogonal conditions.