Materials often fail as a result of the mechanical loads they experience during use. On the molecular level, forces within polymers are distributed unevenly throughout the material, and some polymer subchains experience greater stress than others. In some cases, the forces experienced by these overstressed subchains can trigger chain scission events. Chain scission in turn might nucleate the formation of a microcrack that subsequently propagates, ultimately leading to material failure. In recent years, force reactive functional groups, or mechanophores, have emerged as the basis of a potential strategy for combatting this destructive cascade. The strategy, known as activated remodeling via mechanochemistry (ARM), comprises embedding mechanophores along the polymer backbone or within cross-links, so that otherwise destructive force within an overstressed subchain triggers a constructive, rather than a destructive, response. These demonstrations have spurred a range of important and fundamental questions about stress-responsive remodeling, including how to dissect the complex interplay between material deformation, mechanophore activation, nascent cross-link rupture, mechanochemically triggered cross-link formation, and the impact of various stages of each on the mechanical properties and eventual failure of the material.
The answers to these questions require new mechanophores that not only activate and then cross-link efficiently, but that give clear spectroscopic signatures of their state so that the levels of both activation and cross-linking can be measured in situ and in real time. In this dissertation, we design, explore, and quantify the mechanical reactivity of two families of mechanophores for use in the context of the ARM concept. The first family is based on a substituted cyclobutene scaffold, which undergoes a force-induced electrocyclic ring-opening reaction to unveil butadiene. The second family of mechanophore investigated is based on the ring-opening of an oxabicyclo[2.1.0]pentane (OBP) to reversibly generate a highly colored carbonyl ylide.