Development of an aromatic triamine-based flame-retardant benzoxazine and its high-performance copolybenzoxazines

An aromatic triamine-based flame-retardant benzoxazine (3), which could not be prepared by the traditional approaches, was successfully prepared by a three-step procedure. The first step is the condensation of 2-hydroxybenzaldehyde with an aromatic triamine, forming intermediate (1) with an imine linkage. The second step is the reduction of the imine linkage by sodium borohydride, resulting in intermediate (2) with a secondary amine linkage. The third step is the ring closure condensation of (2), leading to benzoxazine (3). The structures of (1–3) were confirmed by IR, high-resolution mass, 1H and 31P NMR spectra. Benzoxazine (3) was copolymerized with commercial benzoxazines. According to the measurements, thermal properties, flame retardancy, dimensional stability of commercial polybenzoxazines were significantly improved via the incorporation of (3).