A spirocyclic parabanic acid masked N‐heterocyclic carbene as thermally latent pre‐catalyst for polyamide 6 synthesis and epoxide curing

Abstract

1,3‐Dicyclcohexyl‐6,9‐dimethyl‐1,3,6,9‐tetraazaspiro[4.4]non‐7‐ene‐2,4‐dione, a spirocyclic parabanic acid derivative of N,N‐dimethylimidazole, is used as thermally latent, protected N‐heterocyclic carbene (NHC) in polymerizing anhydride‐cured epoxide resins, and azepan‐2‐one, respectively. The protected carbene is synthesized from 1,3‐dimethylimidazolium‐2‐carboxylate in the presence of two equivalents of cyclohexyl isocyanate. In the synthesis of epoxide resin thermosets, this class of latent NHC allows the production of fast and fully cured materials with high crosslinking content. Fast and complete conversion is found in the anionic ring opening polymerization (AROP) of azepan‐2‐one (ε‐caprolactam, CLA) with and without additional activators.