Research on thermal degradation process of p-nitrophenol-based polybenzoxazine

Effect of nitro group on thermal degradation process of polybenzoxazine was explored in this work through investigating p-nitrophenol-aniline-based benzoxazine (np-a) and its polymer (Pnp-a). The DSC and FTIR results show that the polymerization of np-a could complete even after a process at 160 °C for 1 h. TGA results in N2 and air atmosphere indicate that the char yield, thermal and thermo-oxidation stability of Pnp-a were better than those of phenol-aniline-based polybenzoxazine. And the similar DTG curves of Pnp-a in N2 and air were observed, implying that the degradation mechanism of Pnp-a in N2 and air was alike. These suggest that the essence of thermal degradation of Pnp-a in N2 was oxidation degradation. Furthermore, TGA-FTIR results show that the obvious volatilization of CO2 and H2O was detected during the almost whole thermal degradation process of Pnp-a. Py-GC-MS measurements and the structure evolution of Pnp-a during the thermal degradation process demonstrate that CO2 mainly resulted from methylene on Mannich bridge being oxidized by hydroxyl radical. Besides, LOI test shows that the flame retardance of polybenzoxazine copolymer increased with the addition of Pnp-a.