Engineering Benzoxazine/Epoxy/Imidazole Blends with Controllable Microphase Structures for Toughness Improvement

Toughness improvement of thermosetting benzoxazine (BZ) /epoxy (ER) blends is of great significance to expand their applications in the field of high-performance structural parts. Introduction of multiphase structures to the thermosetting blends via in situ reaction induced phase separation is a promising way to improve their toughness. However, the influences of the blend compositions on the phase separation and phase morphology as well as the thermal and mechanical properties of blends are still not clear. Here, we prepared a variety of BZ/ER/imidazole (MZ) ternary blending systems with different compositions and found that phase separation structures, including sea-island, cocontinuous, and phase-inversion morphologies, could be controlled by tuning the composition of ER resins and MZ. At a specific composition of ER resins, increasing the MZ content is prone to form phase separation structures, and the minimum MZ content needed for phase separation increased with the ER content. What is more, when the reactivity difference between BZ and ER (ΔEα) was larger than 40%, phase separation could occur. Finally, the introduction of multiphase morphologies significantly improved the impact strength and well maintained the thermomechanical properties of ternary blends.