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

Abstract

AbstractTwo‐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 ≈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 ≈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.