Radical-Mediated Scission of Thioaminals for On-Demand Construction-Then-Destruction of Cross-Linked Polymer Networks

Two-stage polymerizing-then-degrading networks are achieved by exposure to a single near UV light source, by sequentially performing thiol-ene photopolymerization and radical-mediated thioaminal scission. To understand the mechanisms involved, synthesis of model thioaminal small molecules shows photo-activated thioaminal scission produces thioamide moieties, identifiable by distinct NMR singlets at 3.29 and 3.26 ppm and a Fourier Transform IR (FTIR) peak approximate to 1530 cm(-1). The scission process is proposed to occur via ss-scission of the carbon next to the sulfur atom and is found to be influenced by thiol substitution on the thioaminal, leading to scission conversion increasing from 5 +/- 1 to 39 +/- 3% and scission time decreasing from 6 to 2 min as the thiols become progressively more substituted. Thioaminal scission occurs semi-orthogonally with radical-mediated thiol-ene reactions; the thiol-ene reaction achieves near quantitative yield within the first 0.5 min while thioaminal scission requires a further 5-15 min. This semi-orthogonality is exploited to create two-stage polymerizing-then-degrading networks, with both regimes dependent on total light dose from a single light source and the transition occurring approximate to 2 J cm(-2) under these exposure and polymerization conditions. This work establishes thioaminals as a new photo-mediated scission chemistry and a means to create multi-stage, light-activated networks.

Automated summary

Two-stage polymerizing-then-degrading networks are achieved by sequentially performing thiol-ene photopolymerization and radical-mediated thioaminal scission. Thioaminal scission occurs via ss-scission of the carbon next to the sulfur atom and is influenced by thiol substitution. Additionally, thioaminal scission occurs semi-orthogonally with the radical-mediated thiol-ene reaction.