The Monomer Containing Cyano-Oxazine-Trifluoromethyl Groups for Enhancing Epoxy Resin: Thermal Stability, Flame Resistance and Mechanical Behaviors

To impart high flame resistance, enhanced thermal stability, and low dielectric properties to epoxy resin while maintaining good mechanical behaviors for high-end applications, a monomer (BZPN) containing the characteristic structure of benzoxazine, phthalonitrile, and trifluoromethyl was prepared and added into the Bisphenol A-type epoxy resin (DGEBA)/Dapsone (DDS) combination. The glass transition temperature (T_g) and carbon yield under a nitrogen atmosphere at 800 °C were found to significantly increase from 155 °C, 17.2% to 236 °C, 50.3%, respectively, for the neat EP/DDS and the BZPN-containing material. The UL-94 flammability rating achieved V-0 level when the BZPN content was 19.2 wt.% (EP-BZ-1). The thermal decomposition and flame retardancy mechanism were explored by TGA-FTIR, Raman, and XPS analysis. The fluorine-containing products were found in both the gas phase and the char residue, implying that the •CF₃ radicals played an important role in promoting the flame-retardant behaviors through a radical trapping mechanism. The dielectric constant and dielectric loss of the materials decreased as anticipated. In addition, mechanical testing of carbon fiber-reinforced composites showed that the BZPN-containing resin presented equivalent mechanical behaviors to the neat EP/DDS resin. The synthesized BZPN was proved to be an effective and promising additive for the epoxy-based composite.