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Polybenzoxazine,a new thermosets,is characterized by low water absorption,superior electrical properties and good thermal stability.They have already been applied in many fields.However,the flame retardancy of the polybenzoxazines is not high enough for some fields,such as electronics and aerospace.Flame retardants,synthesized from DOPO [ 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide] or its derivatives,are considered as a promising phosphorus-containing reactive flame retardants.They exhibit many attractive advantages including no halogen,high efficiency,low smoke,no migration,low toxicity,persistence of flame retardant performance.DOPO and its derivatives have been used to improve polybenzoxazine flame retardant.The epoxy resins are widely used as advanced composite matrices in electronic/electrical industries due to superior mechanical properties,good heat resistance and good adhesion to many substrates.A phosphorus-containing benzoxazine( ODOPB-BOZ) was synthesized from 4,4-diaminodiphenyl ether,paraformaldehyde and ODOPO[10-( 2,5-dihydroxyphenyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxidei.A series of composites were obtained by blending BOZ-ODOPB with epoxy resins under different mass mixing ratios.The thermal properties of the composites materials were evaluated by thermogravimetric analysis ( TGA) differential scanning calorimetry( DSC).The results show,the suitable mass ratio of two resins was m BOZ):m EP) =8:2.Composites prepared under this condition presents 5% weight loss at 371℃,10% weight loss of at 382℃ and 62% char yield at 800℃ in N2,Tg at 232.7℃.Epoxy resin exactly react with phenolic hydroxyl groups from ring - opening polymerization of benzoxazine monomers,which can effectively increase the crosslinking density of resin.