The effect of substituent group in allyl benzoxazine on the thermal, mechanical and dielectric properties of modified bismaleimide

Allyl benzoxazine resin (BOZ-A) synthesized from 2,2′-diallyl bisphenol A (DABPA), aniline and paraformaldehyde has been used to improve the mechanical and processing properties of bismaleimide resin. However, the lower heat resistance and the unsatisfactory dielectric properties cannot satisfy the requirements of high-performance composites in aerospace fields. Introducing nonpolar materials into the resin matrix effectively improves the dielectric properties. Inspired by the designability of benzoxazine, a novel allyl benzoxazine resin grafted with trifluoromethyl (BOZ-F) or methyl (BOZ-C) was synthesized and blended with BD-type bismaleimide resin (BDM-C and BDM-F) to explore the effect of substituent groups on the comprehensive performance. Due to the different electronic effects of the substituents, BDM-C possesses higher reactivity with a polymerization temperature of 212.7 °C, which is lower than that of BDM-A (217.8 °C) and BDM-F (226.6 °C). Their respective reactivity also leads to differences in rheological properties. Specifically, BDM-F exhibited the excellent thermal stability with a Tg of 308.3 °C, which is 17.2 °C higher than that of BDM-A. Furthermore, the dielectric constant (Dk) and dielectric loss (Df) of BDM-F at 10.5 GHz decreased to 3.06 and 0.0078 from 3.13 and 0.0114 when compared with BDM-A. In addition, BDM-C demonstrated the highest bending strength of 136.02 MPa. The current study delivers an effective approach to balance the performance of thermosetting resins by regulating substituents, which is valuable for potential application in wave-transparent fields.