Photochemically Activated Thiol-Michael Reactions via a Photolatent N-Heterocyclic Carbene
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While N-heterocyclic carbenes (NHCs) have proven highly effective in various polymerization reactions, the drawback is their high sensitivity towards air and water, which necessitates handling under rigorously anhydrous conditions. In this report, an air-stable two-component NHC photogenerator ─ 2-isopropylthioxanthone (ITX) as photosensitive species and 1,3-bis(mesityl)imidazolium tetraphenylborate (IMesH+ BPh4-) acting as NHC protected precursor ─ has been utilized to organocatalyze thiol-Michael reaction for small molecule and polymer synthesis. The feasibility of photoNHC catalysis in addition reactions involving thiol and ene molecules was investigated using 1H NMR spectroscopy. The synthesis of cross-linked polythioether polymer via a step-growth polymerization was then studied using FTIR spectroscopy, optical pyrometry and gel content measurements.