Cascade Mechanochemical Transformation of a Benzobarrelane Polymer

Designing and understanding the reactivity of individual force-responsive molecules, mechanophores, has been a central topic in polymer mechanochemistry. However, we envision that when certain molecular structures are closely coupled along a polymer backbone, new mechanochemical reactivity that is absent from individual molecules may arise. Herein, we describe a polymer consisting of benzobarrelane repeat units that are connected via backbone alkenes, where force-induced bond scission triggers a radical cascade reaction to transform the polymer backbone structure. Despite the lack of weak covalent bonds or significant ring strain in the benzobarrelane polymer, it achieved similar degrees of mechanochemical transformation as our previously reported polyladderene systems consisting of highly strained repeat units. In contrast, no mechanochemical reaction was observed in benzobarrelane units that are distant from one another along the backbone: the mechanochemistry of barrelane requires immediately connected barrelane units. This work demonstrates the possibility of eliciting novel reactivities by creating cooperative chemical pathways across otherwise inert individual units.