Design and synthesis of anhydride-terminated imide oligomer containing phosphorus and fluorine for high-performance flame-retarded epoxy resins.

[Display omitted] • A novel imide oligomer was applied as a multifunctional co-curing agent for EP. • The cured resins showed satisfactory flame retardancy and dielectric properties. • Thermal and mechanical properties of the cured resins were improved. Challenges remain in the design and construction of robust epoxy thermosets with concurrently improved flame retardancy, thermal, mechanical and dielectric properties. In this work, a novel method has been exploited to synthesize anhydride-terminated imide oligomer containing phosphorus and fluorine (FPI) in the mixed solvents consisting of benzoic acid and acetic acid by single-step reaction. Compared to the ones synthesized by the conventional methods, FPI possessed a much higher content of anhydride groups, and was more suitable to be used as co-curing and flame-retarded agents for epoxy resins. With multifunctional groups, FPI can endow epoxy thermosets with a series of excellent properties. At the loading of 28.5 wt% FPI (only 0.87 wt% phosphorus), the epoxy thermoset (EP/FPI-3) passed the UL-94 V-0 test with the limiting oxygen index (LOI) value of 31.1%. Instead of the reduction in other properties of most polymeric materials after being flame-retarded, the overall performance of EP/FPI-3 was improved, hereinto, the glass transition temperature, heat deflection temperature, 5 wt% mass loss temperature (under N 2) and Young's modulus were increased by 37.2 °C, 42.4 °C, 10.2 °C, 50.6%, respectively, and the dielectric constant, dielectric loss and water adsorption were decreased by 9.9% (100 MHz), 33.3% (100 MHz), 16.2%, respectively, compared to those of the original epoxy thermoset. This work provides a simple and practical way to prepare the flame-retarded epoxy thermosets with improved overall properties by the bespoke multifunctional imide oligomers used as co-curing and flame-retarded agents, and the resulting epoxy thermosets are highly competitive as the advanced electrical materials. [ABSTRACT FROM AUTHOR]