Reaction induced phase separation in thermosetting/thermosetting blends: effects of imidazole content on the phase separation of benzoxazine/epoxy blends

Abstract

A micro-sized phase separation structure was successfully realized in normally homogeneous benzoxazine (BZ)/epoxy (ER) (mass ratio: 80/20) blending systems in situ by enhancing the content of catalyst, imidazole (MZ). To reveal the internal relationships between the content of MZ and the phase separation, the phase morphology, polymerization activity, rheology and relaxation behaviors of BZ/ER blends with different contents of MZ were investigated by means of turbidity observation, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and rheological and dynamic mechanical thermal analysis (DMA), respectively. The results showed that in the BZ/ER/MZ blending system, when the content of MZ was high enough (≥8 wt%), micro-sized ER-rich domains could be obtained, otherwise a homogeneous structure was obtained. What's more, the curing reaction of BZ/ER/MZ blends at 110 °C was mainly associated with the polymerization of ER with MZ. Increasing the MZ content not only increased the reactivity difference between ER and BZ and accelerated the gelation, but also resulted in branched or looser ER networks and relatively low system viscosity, therefore was beneficial to phase separation.