Competitive Study of Novel Triptycene-Containing Benzoxazine Monomers and a Thermoresponsive Linear Main Chain-Type Benzoxazine Copolymer: Synthesis, Polymerization, and Thermal Properties of Their Thermosets

Two novel triptycene-based dioxazine benzoxazine monomers (TB-a and TB-fa) have been synthesized using triptycene-1,4-hydroquinone (TB), aniline/furfurylamine, and paraformaldehyde as raw materials. The chemical structures of both dioxazine benzoxazine monomers were elucidated by 1H and 13C NMR, Fourier transform infrared (FT-IR), high-resolution mass spectroscopy, and elemental analysis. By taking advantage of the furan groups present in TB-fa and the reversibility of the Diels–Alder reaction, 4,4′-bismaleimidodiphenylmethane (DDM-BMI) was used as a comonomer for synthesizing a thermoresponsive linear main chain-type benzoxazine copolymer (TB-fa-co-DDM-BMI). The polymerization processes of oxazine ring-containing monomers and the copolymer were studied by DSC and in situ FT-IR analyses, while the thermal stability and flammability of the resulting thermosets were studied by thermogravimetric analysis and microscale combustion calorimetry. Remarkably, the thermoset derived from the thermoresponsive TB-fa-co-DDM-BMI exhibits the best thermal stability as demonstrated by the Td10 and Yc values of 388 °C and 55% at 800 °C under a nitrogen atmosphere, respectively. Its low heat release capacity value of 31.9 J g–1 K–1 shows its great potential as a good flame retardant agent. The outstanding properties exhibited by the herein presented polybenzoxazines, compared to those of many other reported traditional polybenzoxazines, evidence their potential applications in the design of advanced materials.