Inherently flame retardant epoxy resin is a kind of halogen-free material for making high-performance electronic materials. This work describes an inherently flame retardant epoxy system composed of 4,4'-diglycidyl (3,3',5,5'-tetramethylbiphenyl) epoxy resin (TMBP), 1,2-dihydro-2-(4-aminophenyl)-4-(4-(4-aminophenoxy) phenyl) (2H) phthalazin-l-one (DAP), and hexa(phenoxy) cyclotriphophazene (HPCTP). The cure kinetics of TMBP/DAP in the presence or absence of HPCTP were investigated using isoconversional method by means of nonisothermal differential scanning calorimeter (DSC). Kinetic analysis results indicated that the effective activation energy (E-alpha) decreased with increasing the extent of conversion (alpha) for TMBP/DAP system because diffusion-controlled reaction dominated the curing reaction gradually in the later cure stage. TMBP/DAP/HPCTP(10 wt %) system had higher E-alpha values than those of TMBP/DAP system in the early cure stage (alpha < 0.35), and an increase phenomenon of E-alpha similar to alpha dependence in the later cure stage (alpha >= 0.60) due to kinetic-controlled reaction in the later cure stage. Such complex E-alpha similar to alpha dependence of TMBP/DAP/HPCTP(10 wt %) system might be associated with the change of the physical state (mainly viscosity) of the curing system due to the introduction of HPCTP. These cured epoxy resins had very high glass transition temperatures (202-235 degrees C), excellent thermal stability with high 5 wt % decomposition temperatures (>340 degrees C) and high char yields (>25.6 wt %). (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 1397-1404, 2009