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Polybenzoxazines have attracted increased attention from academic and industrial researchers for decades due to their exceptional properties. However, developing efficient methodologies for reducing the polymerization temperature of benzoxazines still remains a significant challenge. Here we report a novel class of polycyclic 1,3-benzoxazine resins containing a unique fused-ring structure, which exhibit significantly lower curing temperatures compared to conventional benzoxazines without adding any initials or catalysts. Three mono- and one bis-oxazine ring-containing polycyclic benzoxazines were successfully synthesized via N,O-acetal formation reactions. Their chemical structures were characterized by Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR), and high-resolution mass spectroscopy (HR-MS). The ring-opening polymerization behaviors were confirmed and investigated by differential scanning calorimetry (DSC) and in situ FT-IR. In addition, the thermal stability and flammability of their resulting thermosets were evaluated by thermogravimetric analysis (TGA) and microscale combustion calorimetry (MCC). Notably, the thermoset derived from the bis-oxazine polycyclic monomer demonstrates comparable performance as poly(BA-a) with a Td10 of 300 °C and a heat release capacity (HRC) value of 120 J·g–1·K–1. With this work, we have developed the polycyclic benzoxazine family for the first time, and their intrinsically low curing temperature and good thermal properties are evidence of their potential applications in high-performance areas.
Yang et al. (Fri,) studied this question.