One-pot synthesis of tetramethyl biphenyl backboned hyperbranched epoxy resin as an efficient toughening modifier for two epoxy curing systems

In this article, an approach to toughen epoxy thermosets with hyperbranched epoxy resin is presented. First, three tetramethyl biphenyl backboned hyperbranched epoxy resins (BPHBEs) were synthesized through a simple one-pot A₂ + B₃ polycondensation reaction. Then, they were incorporated into epoxy/anhydride and epoxy/jeffamine curing systems, respectively. The curing behavior was investigated by differential scanning calorimetry, which reveals that the adding of BPHBE to the formulation would not much affect the curing process. The influence of BPHBE on the mechanical and thermomechanical properties of both epoxy/anhydride and epoxy/jeffamine systems was studied. The results show that BPHBE can significantly toughen both two systems without much trade-offs in their strength, modulus and T_g. While the initial decomposition temperature of the cured thermosets slightly drops. Owing to the miscible backbone structure and terminal epoxy groups, no phase separation was observed in SEM.