Design of a self-healing and flame-retardant cyclotriphosphazene-based epoxy vitrimer

Reprocessability and reparability are possible with thermoplastics but are rarely encountered with thermosets, which are used much more frequently in many applications other than thermoplastics. A novel cyclolinear cyclotriphosphazene-based epoxy resin (CTP-EP) was successfully synthesized, characterized, and cured by the addition of the disulfide-containing aromatic diamine hardener DTDA to form a new epoxy vitrimer, CTP-EP/DTDA. This epoxy vitrimer behaves as a typical thermoset at ambient conditions but can be quickly reprocessed at elevated temperatures by hot-pressing, similar to a thermoplastic. The outstanding multi-self-healing performance of this dynamic epoxy system is attributed to the radical-mediated aromatic disulfide exchange mechanism. After repairing itself three times, this epoxy system still had a high healing efficiency of 89.8%. In addition, this newly obtained epoxy system also possesses good thermal stability and excellent flame retardancy due to the cyclotriphosphazene structures in the epoxy resin. The multifunctional properties of this material make it a promising candidate for a variety of applications, such as fiber-reinforced polymer composites in the aerospace and automotive industries.