Hyperbranched Epoxy Resin With Flexible Siloxane Skeleton for Improving the Comprehensive Performance of Epoxy Thermosets

ABSTRACT Hyperbranched epoxy resins are efficient toughening modifiers for epoxy thermosets. However, enhancing the mechanical/thermomechanical properties while improving the toughness of the epoxy thermosets remains a challenge. Herein, a new hyperbranched epoxy resin containing a flexible siloxane skeleton (HBPSER) was synthesized for improving the comprehensive performance of epoxy thermosets. Specifically, the phenolic hydroxyl‐terminated hyperbranched precursor (HBPS) was first synthesized using 1,3‐bis(chloromethyl)‐1,1,3,3‐tetramethyldisiloxane (A 2 ‐type monomer) and 3,5‐dihydroxybenzoic acid (CB 2 ‐type monomer), followed by the surface modification with epichlorohydrin to afford the HBPSER. The HBPSER was then utilized for modification of diglycidyl ether of bisphenol A (DGEBA)/methylhexahydrophthalic anhydride (MeHHPA) thermosets. Compared to the neat DGEBA thermoset, the 8 wt% HBPSER‐modified epoxy thermoset showed a 139.6%, 99.6%, 88%, 268.2%, 22.8%, and 2.8% increase in impact strength, elongation at break, critical stress intensity factor ( K IC ), critical crack propagation energy release rate ( G IC ), tensile strength, and glass transition temperature ( T g ), respectively. In addition, the dielectric constant and dielectric loss were reduced by 41.3% and 51.6%, respectively. Moreover, the flame retardancy of the epoxy thermosets was also improved with the addition of HBPSER. This comprehensive modification performance was caused by the synergistic effects of intramolecular cavities, rigid phenyl units, and flexible siloxane segments in HBPSER.