The high-temperature sparks from the cutting or welding will decompose the print circuit board (PCB) use epoxy resin. To explore the influence of curing agents on the oxygen participated thermal decomposition mechanisms of the epoxy resin, the epoxy-O 2 models, which are cured by 3,3-DDS, 3,3-SDA, 3,3-SSDDS, and 4,4-DDS, respectively, were first established. After geometric optimization and relaxation, the permeabilities of O 2 in the crosslinked epoxies are analyzed via gas molecular tracking. And then, the ReaxFF-based MD simulation is applied to track the initial reactions of the pyrolysis. The results show that the O 2 is much easier to transfer in the crosslinked epoxy matrixes at the spark temperature. The epoxy rings at the end of epoxy chains are likely to be attacked by the oxygen under high temperature, releasing the tens of CH 2 O, as the dominant product type. More than 65 wt.% large-size molecules, containing 80+ carbon atoms, remained in the systems, indicating a nice thermal resistance. Based on the DFT calculation, the 4SDA-type epoxy chain shows the highest reactivity with oxygen, which the lowest HOMO energy. 4,4-SDA is going to protect the carbon backbones of epoxy by scarifying, at the initial pyrolysis
