Preparation and enhanced flame retardancy of co‐polybenzoxazines containing diacetal structure

Abstract

AbstractA comparative study on the flame retardancy of two polybenzoxazines with and without a diacetal structure, p(A) and p(B), is firstly carried out by microscale combustion calorimeter (MCC). It is proved that the presence of the diacetal structure can endow p(A) with good flame retardancy with a low heat release capacity (HRC). Then, the monomer of this diacetal containing p(A), A‐boz, is used to modify a typical diamine type benzoxazine (M‐boz) to improve its flame retardancy. The effects of A‐boz with different ratios on curing behavior, heat resistance and thermal stability of the co‐polybenzoxazines of M‐boz and A‐boz, p(M/A)s, are analyzed by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Furthermore, the flame retardancy of p(M/A)s is investigated by UL‐94 test, limiting oxygen index (LOI) and MCC, and the degradation and flame retardant mechanisms are investigated by scanning electronic microscopy (SEM), Raman spectra and TGA‐FTIR. When the addition amount of A is 20 wt%, the LOI value of p(M/A) is as high as 39.5% and its flame retardant rating reaches UL‐94 V‐0. In addition, the mechanical properties of p(M/A)s are tested. The results suggest that the Tg and char yield at 800°C in N2 of p(M/A)s increase from 210 to 243°C and 45% to 51%, respectively. This work suggests that the incorporation of the diacetal structure is an effective strategy to improve the flame retardancy of resins.