Phosphorus‐Free Flame‐Retardant Polybenzoxazine Enabled by Low‐Loading Trialdehyde Compound

To improve the flame resistance of a standard diamine‐based polybenzoxazine [poly(PH‐ddm)], a trialdehyde compound (TPBA) with a triazine ring was synthesized and added with different contents as a distinctive flame retardant. The curing behaviors of the resulting resins (PH‐ddm/TPBA) were analyzed using differential scanning calorimetry (DSC). Concurrently, the thermal properties of the polymers were investigated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). The incorporation of TPBA facilitated additional cross‐linking reactions due to the presence of aldehyde groups, which led to a higher cross‐linking density within the material. The glass transition temperature (T g ) and char yield (Y c ) of poly(PH‐ddm/TPBA‐6) were increased to 243°C and 46.2%, respectively. Moreover, the flame retardancy of the modified polybenzoxazines was characterized by the UL‐94 test, limiting oxygen index (LOI) test, and Micro combustion calorimetry (MCC). The addition of only 2 wt% of TPBA enabled the polybenzoxazine to achieve a V‐0 rating. In addition, the mechanical property of these polybenzoxazines was studied, and the flexural strength of 120 MPa can be obtained. In this work, the polybenzoxazine with excellent flame retardancy obtained by adding a low‐loading trialdehyde compound can be used in aviation and electronics fields.