In the field of sustainable materials, photodegradable polymer networks are attractive due to their inherent spatiotemporal control and selectivity in degradation. Expanding the toolbox of available photodegradable chemistries is an important step in this push towards sustainable polymers. This work explored thioaminal groups, which cleave into thioamides via radical reaction, as moieties that can enable polymer network photodegradation. Model small-molecule studies showed thioaminal groups underwent ß-scission in the presence of catalytic amounts of Irgacure 819 and exposure to 400-500 nm light, resulting in thioamides. This radical-mediated cleavage of thioaminals was found to be semi-orthogonal with the thiol-ene combination reaction, occurring only after near quantitative consumption of ene groups. Synthesis of a monomer containing both thiol-ene and thioaminal active functional groups enabled the polymerizing thiol-ene reaction to achieve quantitative conversion within 30 s followed by a thioaminal degradation taking 15 min. This semi-orthogonality was then employed in polymer networks to achieve a distinct polymerization and degradation regime controlled by light dose. Varying the light intensity from 1 to 30 mW/cm<sup>2</sup> granted control over degradation time ranging from 5 to 60 min. Mass loss studies of this network showed photodegradation was well predicted by previously established statistical models. Additionally, the degradation mechanism could transition from surface to bulk degradation by changing optical density via decreasing film thickness from 100 to 25 m. Work of this nature establishes thioaminal-containing polymers as new photodegradable networks specifically and radical-induced thioaminal cleavage as a new chemistry tool generally.

Radical-induced degradation of thioaminals to create two-stage photodegradable networks

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.