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

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 con-taining 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 N2) and Young's modulus were increased by 37.2 degrees C, 42.4 degrees C, 10.2 degrees 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.