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Effect of Interaction between Transition Metal Oxides and Nitrogen Atoms on Thermal Stability of Polybenzoxazine

To investigate the interaction of transition metal oxides with polybenzoxazine and their influence on the thermal degradation mechanism of polybenzoxazine, transition metal oxides Y2O3, La2O3, Pr6O11, and Gd2O3 were added to benzoxazine monomer based on p-cresol and aniline to prepare polybenzoxazine composites. The chemical structures and final polymerization extent of polybenzoxazine and its composites were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and differential scanning colorimetry (DSC). The molecular weights of these cured samples were determined by gel permeation chromatography (GPC). The influence of transition metal oxides on the thermal properties of polybenzoxazine matrix was investigated using dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), thermogravimetric analyzer interfaced with Fourier transform infrared spectroscopy (TG-IR), and (pyrolysis-gas chromatography-mass spectrometry) Py-GC-MS. The results show that transition metal oxides can form coordination interactions with the nitrogen atoms of polybenzoxazine. The coordination interaction can anchor the aniline and make the molecular weights of polybenzoxazine matrix increase, which delays evaporation of aniline during thermal degradation, improves the char yield at 800°C, and increases the glass transition temperatures (Tg) of polybenzoxazine composites.