Making Benzoxazine Greener and Stronger: Renewable Resource, Microwave Irradiation, Green Solvent, and Excellent Thermal Properties

Abstract

To fulfill the principles of green chemistry, renewable magnolol and furfurylamine were taken to synthesize benzoxazine under microwave irradiation using poly(ethylene glycol) (PEG) as the solvent. The reaction was monitored by the yield of target compound under varied conditions. Only in 5 min, the yield of target benzoxazine monomer (M-fa) could be high up to 73.5% in PEG 600 system, indicating the desired advantage of microwave irradiation for benzoxazine synthesis. After the chemical structure of M-fa was confirmed, its polymerization behavior, processability, and thermo-mechanical properties were carefully evaluated. The cured resins presented a high glass transition temperature of 303 °C and exceedingly good thermal stability with 5% and 10% weight-loss temperature higher than 440 and 463 °C, respectively, and a char yield of 61.3%. In addition, M-fa demonstrated viscosity lower than 1 Pa·s during the temperature range from 100 to 194 °C, which indicated its good processability. This work provided us a strategy for the synthesis of high bio-based content high-performance thermosets under environmental-friendly conditions, that is, microwave-assisted heating method and green solvent.