Developing non-halogen and non-phosphorous flame retardant bismaleimide resin with high thermal resistance and high toughness through building crosslinked network with Schiff base structure

High flame retardancy has become a necessary property for heat-resistant thermosetting resins (HRTRs) in many cutting-edge fields. However, developing HRTRs with excellent flame retardancy through sustainable strategy (halogen-free and phosphorus-free) is still a great challenge. Herein, a novel halogen-free and phosphorus-free allyl compound with Schiff base structure (PDM) was efficiently synthesized from biobased protocatechualdehyde, and then four new flame retarding bismaleimide resins (BP1, BP2, BP3, BP4) were developed by building crosslinked network with PDM. The molar ratio of allyl to imide has a significant effect on performances of BP resins, BP2 resin (its molar ratio of allyl to imide is 0.86) shows the best integrated performances, it has not only high impact strength (14.37 +/- 1.1 kJ/m(2)), but also the highest glass transition temperature (343.5 degrees C) and limiting oxygen index (36.4%) among halogen-free and phosphorus-free flame retarding bismaleimide resins reported so far. The investigation on flame retardant mechanism of BP resins shows that the mechanism includes condensed-phase and gas-phase flame retarding effects.

Automated summary

High flame retardancy is essential for heat-resistant thermosetting resins in cutting-edge fields. However, developing resins with excellent flame retardancy through sustainable strategies remains a challenge. In this study, a novel halogen-free and phosphorus-free allyl compound was synthesized and used to develop new flame retarding bismaleimide resins. Among them, BP2 resin showed the best integrated performances, including high impact strength, glass transition temperature, and limiting oxygen index.