The authors reported that the completely cured materials could achieve high char yield and high Tg. The thermally activated curing of BZCN follows multiple curing mechanisms via the ring-opening polymerization of oxazine rings and the triazine ring-formation of cyano groups, which contribute to the stability of this polymer. More recently, thermal stability of 9,10-dihydro-9-oxa-10-phosphaphenanthrene (DOPO)-containing polybenzoxazine was reported by Sponton [14]. Thermal stability of the phosphorus-containing polybenzoxazines was evaluated by examining their degradation temperature (Td) and char yield. The Td at 5% weight loss and char yield under nitrogen atmosphere at 750 °C of the modified polybenzoxazines were reported to be 332 °C and 25%, respectively. However, disadvantages of the modification of the molecular structure of the benzoxazine resins to obtain high performance polymer include difficulty of the resin preparation, the purification process, and the high cost of raw materials used.