In(NO3)3 catalyzed curing reaction of benzoxazine

Benzoxazine is a new kind of thermoset resin with excellent properties, but it suffers from high curing temperature and low char yield in the presence of catalyst without halogen. In(NO3)(3) was herein used for the first time to efficiently catalyze the curing reaction of benzoxazine and to elevate the char yield at 800 degrees C. The reaction of benzoxazine was catalyzed by In(NO3)(3) after stirring at 35 degrees C for 300 min, and the initial curing temperature decreased to 151 degrees C. Polybenzoxazine/In(NO3)(3) showed higher thermal stability and char yield at 800 degrees C (increased by 7.5%) compared with those of polybenzoxazine. The possible pathway of coordination bonding between In3+ and benzoxazine was proposed. In the cross-linking process, two different structures, that is, the N, O-acetal bridge structure and arylamine Mannich bridge structure formed at 35 degrees C, both existed, which ultimately affected the thermal stability of the cured product.