An Organometallic Flame Retardant Containing P/N/S-Cu²⁺ for Epoxy Resins with Reduced Fire Hazard and Smoke Toxicity

Epoxy resins (EPs) have superior physical and chemical features and are used in a wide range of applications in everyday life and engineering. However, its poor flame-retardant performance has hindered its wide application. Over the past decades of extensive research, metal ions have received increasing attention for their highly effective smoke suppression properties. In this work, we used an "aldol-ammonia condensation" reaction to structure the Schiff base structure, together with grafting using the reactive group on 9,10-dihydro-9-oxa-10-phospha-10-oxide (DOPO). Then, Cu²⁺ was used to replace Na⁺ to obtain DCSA-Cu flame retardant with smoke suppression properties. Attractively, DOPO and Cu²⁺ can collaborate, thus effectively improving EP fire safety. At the same time, the addition of a double-bond initiator at low temperatures allows small molecules to form in situ macromolecular chains through the EP network, enhancing the tightness of the EP matrix. With the addition of 5 wt % flame retardant, the EP shows well-defined fire resistance, and the limiting oxygen index (LOI) reaches 36% with a significant reduction in the values of peak heat release (29.72%). In addition, the glass-transition temperature (T_g) of the samples with in situ formations of macromolecular chains was improved, and the physical properties of EP materials are also retained.