Enhanced Flame Retardancy and Ablation Resistance of Polybenzoxazines Modified by Boron-Containing Spiro Bisphenol

The requirement for good flame retardancy is urgent for polymers. In this work, a boron-containing spiro bisphenol (PHB) was synthesized and used to modify a typical diamine-type benzoxazine (Db). The effects of PHB with different ratios on the curing behavior, heat resistance, and thermal stability of the modified polybenzoxazines (PDb-PHBs) were studied by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). Additionally, the flame retardancy of PDb-PHBs was investigated by the UL-94 test, limiting oxygen index (LOI), and microcalorimetry (MCC), and the degradation and flame retardancy mechanisms were investigated by scanning electron microscopy (SEM), Raman spectra, and thermogravimetric analysis-infrared (TGA-FTIR) spectra. When the addition amount of PHB was 13 wt %, the flame retardancy rating of PDb-PHB reached V-0 and the LOI value was as high as 35.2%. In addition, the ablation resistance of PDb-PHBs after carbonization was tested. This work suggests that the incorporation of this boron-containing compound is a proficient approach to enhance the flame retardancy and ablation resistance of polymers.