Mechanochemically Assisted Release of Hydrogen Fluoride and its Application in Triggered Polymer Degradation

Abstract

Hydrogen fluoride (HF) is a versatile reagent for material remodeling, with applications in self-immolative polymers, remodeled siloxanes, and degradable polymers. The responsive, in situ generation of HF in materials therefore holds promise for new classes of adaptive material systems. Here, we report the mechanochemically coupled generation of HF from 2-methoxy-gem-difluorocyclopropane (MeO-gDFC) mechanophores in polymers. Pulsed ultrasonication of a MeO-gDFC containing polymer leads to one equivalent of HF release per MeO-gDFC activation. The mechanochemical reactivity of MeO-gDFC is quantified by single molecule force spectroscopy, and force-coupled rate constants for ring opening reach ~36 s-1 at a force of ~890 pN, 400 pN lower than is required in dialkyl gDFC mechanophores that lack the methoxy substituent. The SMFS and sonication results suggest that MeO-gDFC is a more efficient mechanophore source of HF than its 2-methoxy-gem-dichlorocyclopropane analog is of HCl, in contrast to expectations based on trends in force-free reactivity. Finally, the HF produced mechanically accelerates the degradation of a copolymer containing both MeO-gDFC (3 mol%) and an HF-cleavable silyl ether (25 mol%). The MeO-gDFC mechanophore thus provides a mechanically coupled mechanism of releasing HF for polymer remodeling pathways that complements previous thermally driven mechanisms.