Synthesis and thermal properties of novel bismaleimides containing cardo and oxazine structures and the thermal transition behaviors of their polymer structures

In this work, three bismaleimides containing cardo and ortho-oxazine structures, with dual advantages of bis-maleimide and benzoxazine resin, were synthesized. Their chemical structures were characterized by Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The kinetics of curing and kinetic model were investigated by non-isothermal differential scanning calorimetry. The curing reaction of the bismaleimide was studied by in-situ FT-IR spectroscopy. Studies showed that both bismaleimide and benzoxazine provided the new structure with better thermal stability and solubility, compared to similar type of materials and commercial bismaleimides. Additionally, the further thermal rearrangement of the internal structure of the polymer at high temperature formed a benzoxazole structure with higher thermal stability. The rearrangement due to thermal changes was confirmed by in-situ FT-IR and solid-state 13C-NMR spectroscopy. Microscale combustion calorimetry (MCC) showed that both, bismaleimide and benzoxazole resins, were formed after thermal rearrangement and had excellent flame-retardant properties.