Hyperbranched flame retardant for epoxy resin modification: Simultaneously improved flame retardancy, toughness and strength as well as glass transition temperature

Endowing epoxy resins with simultaneously improved flame retardancy, toughness and strength as well as glass transition temperature (Tg) is a big challenge for us. Herein, a hyperbranched flame retardant (HBFR) with rigid backbone structure was synthesized through a facile strategy. Upon the incorporation of HBFR, the modified diglycidyl ether of bisphenol A (DGEBA) with phosphorus content of only 0.24 wt% exhibited better flame retardancy beyond expectation, showing UL-94 V-0 rating and limited oxygen index (LOI) above 32.6 vol%. Meanwhile, the modified epoxy resin demonstrated superior toughness, indicated by the more than 96% increment in impact strength both at 25 and −196°C, due to the enlarged free volume originated from hyperbranched structures. Furthermore, the Tg, flexural strength and modulus of modified epoxy systems were also significantly increased because of the rigid backbone structure and high crosslinking density afforded by HBFR. This work provided us an attractive strategy for simultaneously improving the flame retardancy, toughness, Tg and strength of commercial epoxy resins.