Enhancing the toughness of polybenzoxazines through multiple sacrificial bonds for improved overall performance

The toughening modification of polybenzoxazine is a crucial approach for expanding its application. However, enhancing the toughness of polybenzoxazine poses challenges in concurrently improving comprehensive properties, such as thermal stability, while reducing the curing temperature. To address this issue, we designed a new polyurethane (CIPU) rich in hydrogen bonding and metal coordination bonding and blended it with benzoxazines to tough polybenzoxazine while enhancing their properties across various aspects. Specifically, the addition of 10% CIPU to benzoxazines increased the toughness of polybenzoxazines by 165.3%, attributed to the relative softness of CIPU and multiple sacrificial bonds. Furthermore, the coordination of free In3+ resulted in a significant enhancement in thermal stability and decrement in curing temperature, evidenced by the increase in residual carbon from 30% to 37% at 800 °C and a decrease in the onset of curing temperature from 246.9 °C to 170.7 °C. This work not only introduces a new system for toughening benzoxazine, but also provides unique insights into hydrogen bonding as well as metal-ligand bonding on toughing thermoset resins.