Quadruple hydrogen bond motif-toughened polybenzoxazine with improved comprehensive performances

As a new thermosetting resin, polybenzoxazine has attracted extensive attention because of its excellent properties. However, the biggest challenge of polybenzoxazine is the balance among impact strength, thermal stability, and processability. In this work, we first introduced a 2-ureido-4[1H]-pyrimidone (UPy, containing quadruple hydrogen bonds) dimer into benzoxazine to tackle this challenge. In the blends containing 3 wt% UPy, its toughness and thermal properties have been simultaneously improved, while maintaining a high modulus and a negligible increasement in viscosity. The impact strength and the glass transition temperature ( T g ) reach 16.39 kJ·m −2 and 221 °C, which are 172% and 10 °C higher than that of polybenzoxazine, respectively. Meanwhile, this strategy was extended to carbon fiber surface modification to enhance the interfacial adhesion between fibers and resins. The mechanical properties of modified fiber composites are significantly improved. Furthermore, we firstly designed the cyclic flexural experiment of material and tried to propose an effective method to verify the effect of hydrogen bond dynamics on flexural properties of polybenzoxazine. Here, we not only provide a new way to get a balance among different properties of polybenzoxazine but also give a broad insight on the application of additional hydrogen bonds in thermoset resins. Graphical Abstract The improved comprehensive performances of polybenzoxazine were realized by introducing quadruple hydrogen bond motif.