Synthesis, polymerization, and thermal properties of novel oxazine-functional bismaleimides and their conversion to high performance benzoxazole resins

In this work, three bismaleimides containing cardo and ortho -oxazine structures, with dual advantages of bismaleimide and benzoxazine resins, were synthesized. Their chemical structures were characterized by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The polymerization behaviors of bismaleimides were investigated using non-isothermal differential scanning calorimetry and in situ Fourier transform infrared spectroscopy. Results showed that the inclusion of both, bismaleimide and benzoxazine, provided a new structure with better thermal stability and solubility, as compared to the same type and commercial bismaleimides. The ortho-oxazine functionalized bismaleimide resin exhibited excellent thermal stability up to 440°C, whereas the carbon residue rate reached 73% at 800°C. Additionally, further thermal rearrangement of the internal structure of the polymer at high temperature provided a benzoxazole structure that had better thermal stability. The rearrangement due to the thermal changes was confirmed by in situ FTIR and solid-state 13 C-NMR spectroscopy. Based on the micro calorimetry characterization, it is found that both the bismaleimide and the benzoxazole resins formed after thermal rearrangement have excellent flame-retardant properties.