Construction of epoxy resin with enhanced flame retardancy, mechanical properties, and satisfactory transparency based on a novel bi-DOPO and hydrogen-bonding network

Establishment of high-performance epoxy resin with satisfactory fire safety, mechanical properties, and excellent transparency is urgently desirable, but still remains significant challenges. Herein, a super-tough yet high flame retardant epoxy resin (EP/BTD) was designed and prepared by incorporating bi-DOPO structure and hydrogen-bonding networks. Although the phosphorus content was only 0.69 wt% (10 wt% of bi-DOPO flame retardant [BTD]), EP/BTD-10 showed a high limiting oxygen index value (33.4%), satisfactory UL-94 rating (V-0), and good heat suppression ability (total heat release [THR] and peak heat release rate [PHRR] reduced to 29.0% and 42.2%, respectively). Furthermore, the flame retardant mechanism of EP/BTD was illustrated and attributed to dual-phase fire-retardant effect. Additionally, EP/BTD-7.5 featured notably mechanical properties, of which the tensile strength, elongation at break and impact strength increased by 44.6%, 40.0%, and 232.6%, respectively, due to hydrogen-bonding network and π–π interaction. More importantly, EP/BTD maintained high visible light transmittance and excellent UV-blocking properties. In summary, this work provided a guidance for the development of high-performance epoxy resin and was expected to expand the practical applications.