A ReaxFF MD based effect investigation of diamino curing agents in the initial thermo-oxidative pyrolysis of epoxy resins

•The oligomer-diamine-oligomer type cured epoxy chains with varied diamino curing agents were established.•The un-xlinked epoxy rings at the end of chains are most likely to be attacked in the high-temperature oxygen environment.•CH2O is the dominant product generated from the thermo-oxidative pyrolysis of epoxy resins.•In the initial stage of 1300 K pyrolysis, the crosslinked epoxy matrixes would be destroyed, with carbon backbones stable.•4,4-SDA curing agents encouraged the thermo-oxidation resistance by sacrificing themselves.