Abstract
It is highly desired yet very challenging to overcome the flammability and brittleness of epoxy resin without compromising its glass transition temperature (Tg). Herein, an epoxy-terminated hyperbranched flame retardant (EHBFR) was designed and synthesized from 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and renewable protocatechualdehyde as well as guaiacol. When the synthesized EHBFR was taken to modify diglycidyl ether of bisphenol A (DGEBA), it is found that the incorporation of EHBFR remarkably improved its fire safety, endowing it with a UL-94 V-0 rating and a limiting oxygen index (LOI) of 33.0 vol%. Meanwhile, the notched impact strength of modified DGEBA at 25 and −196 °C (quenched by liquid nitrogen) exhibited significant increment by 135% (from 3.39 to 7.97 KJ/m2) and 114% (from 2.34 to 5.01 KJ/m2), respectively. Moreover, the Tg of modified epoxy resin did not show any decrease, and even increased from 172 to 194 °C when the content of EHBFR was 10 wt%, due to the synergistic effect of rigid DOPO-containing groups and high crosslink density. This work offers an efficient strategy for constructing high-performance epoxy thermosets with excellent flame retardancy, superior toughness and strength, as well as elevated Tg.
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