Thermal degradation behavior and gas phase flame-retardant mechanism of diamine-based polybenzoxazine/polyhexahydrotriazine interpenetrating polymer network

• The gas phase flame-retardant mechanism of diamine based polybenzoxazine /polyhexahydrotriazine interpenetrating polymer network was studied. • Poly(PH-ddm)/PHT IPN would release self-extinguishing gases, such as NH 3 and CO 2 , and these gases could effectively decrease the heat release. It is an important research direction to improve the flame retardant properties of polymers. Benzoxazine resins have attracted a great deal of interest due to their good thermal property, but the brittleness hindered their further application. A high-toughness diamine-based polybenzoxazine/polyhexahydrotriazine interpenetrating polymer network (poly(PH-ddm)/PHT IPN) have been prepared successfully in our group. In this paper, the flame-retardant mechanism of the poly(PH-ddm)/PHT IPN was discussed. Its flammability property and the thermal decomposition mechanism were measured and analyzed with Cone Calorimeter, Thermogravimetric Analysis-Fourier Transform Infrared Spectroscopy (TGA-FTIR), and Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS). The results illustrated that little heat was released during the ignition process of the cured resin. The main gas including NH 3 and CO 2 were generated during the thermal decomposition. With the release of these self-extinguishing gas that insulate the materials from oxygen and take away the burning heat, the poly(PH-ddm)/PHT IPN with the hexahydrotriazine structure exhibits good gas phase flame retardance.