Two novel halogen-free, phosphorus-free, and intrinsically flame-retardant benzoxazine thermosets containing electron-withdrawing bridge groups

Two novel furfurylamine type benzoxazine prepolymers are firstly synthesized from 4,4'-bishydroxydeoxybenzoin (BHDB) and 4,4'-dihydroxybenzophenone (DHBP). Both BHDB- and DHBP-based polybenzoxazines present accelerated curing behaviors, high glass transition temperatures, and very low heat release capacity values, resulting from the introduction of electron-withdrawing groups and furan rings. It is especially noteworthy that the flame retardancy of DHBP-based polybenzoxazine is classified as UL-94 V-1 grade, whereas that of BHDB-based polybenzoxazine is evaluated to be UL-94 V-2 grade. Hence, DHBP is considered as an alternative to BHDB for benzoxazine preparation because of its similar chemical structure, competitive price, high efficiency preparation, and outstanding flame resistance. Therefore, this work not only provides an economical and effective strategy for the preparation of halogen-free, phosphorus-free, and intrinsically flame-retardant benzoxazine resins but also provides important insight into the effects of electron-withdrawing bridge groups on the curing behavior and thermal and flame-retardant properties of benzoxazine resins.