Syntheses of flame-retarding 4-phosphonatomethyl-2,6-dibromophenyl trimellitate anhydrides and their reactivities toward epoxy resin

4-Phosphonatomethyl-2,6-dibromophenyl trimellitate anhydrides (HDBBP–TMA) were prepared by the condensation of 4-chloroformyl phthalic anhydride with corresponding 4-hydroxy-3,5-dibromobenzyl phosphonates (HDBBP). These materials could be used to produce excellent flame retardance in epoxy resins when the substances were chemically combined with the polymer. The reactive-type HDBBP–TMA showed much better phosphorus–bromine synergistic effects on the flame retardancy of epoxy resins than the additive-type compounds such as HDBBP or the mixture of bromo compound (such as 2,6-dibromo-p-cresol) and phosphorus compound (such as triphenyl phosphite). Meanwhile, the oxygen index of cured epoxy resin was proved to be relative to the extent of crosslinking. Reactivities of HDBBP–TMA toward epoxy were also studied by rheometer in comparison with those of trimellitic anhydride and its derivatives such as 4-methylphenyl trimellitate anhydride and 4-methyl-2,6-dibromophenyl trimellitate anhydride.