We propose three approaches to obtain flame-retardant benzoxazines. In the first approach, we synthesize a novel benzoxazine (dopot-m) from a phosphorus-containing triphenol (dopotriol), formaldehyde, and methyl amine. Dopot-m is copolymerized with a commercial benzoxazine [6',6-bis(3-phenyl-3,4-dihydro-2H-1,3-benzoxazineyl)methane (F-a)] or diglycidyl ether of bisphenol A (DGEBA). The thermal properties and flame retardancy of the F-a/dopot-m copolymers increase with the content of dopot-m. As for the dopot-m/DGEBA curing system, the glass-transition temperature of the dopot-m/DGEBA copolymer is 252 degrees C, which is higher than that of poly (dopot-m). The 5% decomposition temperature of the dopot-m/DGEBA copolymer increases from 323 to 351 degrees C because of the higher crosslinking density caused by the reaction of phenolic OH and epoxy. In the second approach, we incorporate the element phosphorus into benzoxazine via the curing reaction of dopotriol. and F-a. After the curing, the thermal properties of the F-a/dopotriol copolymers are almost the same as those of neat poly(F-a), and this implies that we can incorporate the flame-retardant element phosphorus into the polybenzoxazine without sacrificing any thermal properties. In the third approach, we react dopo with electron-deficient benzoxazine to incorporate the element phosphorus. After the curing, the glass-transition temperatures of polybenzoxazines decrease slightly with the content of dopo, mainly because of the smaller crosslinking density of the resultant polybenzoxazines. (c) 2006 Wiley Periodicals, Inc

Two new phenol‐type curing agents, (3) and (4), were synthesized by the condensation of 4 (or 2)‐hydroxybenzaldehyde and 4‐aminophenol, followed by the addition of DOPO to the resulting imine linkage. Two reaction mechanisms, conjugate‐addition and carbocation mechanisms, were proposed. The fact that the ratio of the configuration of the two diastereomers depends on the reaction solvent indicates that the carbocation mechanism is the more reasonable one. (3) and (4) served as curing agents for epoxy resins, and the resulting epoxy thermosets exhibited good flame retardancy, and moderate Tg and thermal stability. The nitrogen‐phosphorus synergistic effect explains the high flame retardancy.magnified image

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