Mechanistic Insights into Mechanochemically Triggered Polymer Degradation

Yixin Hu, Ph.D. Candidate Stephen L. Craig Ph.D., Advisor Abstract: Mechanochemistry offers a novel pathway to alter polymer properties, and gem-dihalocyclopropanes (gDHCs) have emerged as key mechanophores for a range of purposes. I will present a polymer system that combines an acid-sensitive, hydrolytically unstable enol ether backbone and a gem-dichlorocyclopropane (gDCC) mechanoacid. This combination enables the polymer to release HCl in response to external force, catalyzing its own deconstruction. Further investigations demonstrate the potential of HF release for material transformation. We found that mechanical force initiates a fluorine migration in main-chain alkoxy and side-chain methoxy substituted gDFC mechanophores; however, only the main-chain substituted gDFC releases HF following activation. The HF release occurs via a hydrolytic process that is acid-catalyzed, creating a self-amplifying reaction cascade for enhanced chain degradation. Finally, single molecule force spectroscopy was utilized to compare the impact of different alkoxy substituents on gDCC and gDFC mechanochemistry, and we observe subtle and unexpected differences in force sensitivity based on the positioning of the alkoxy groups.