One stone, three birds: DOPO-based hollow polymer microspheres achieving superior flame retardancy, mechanical performance, and dielectric properties in high-performance epoxy composites

Although 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives have been widely utilized as flame retardants in epoxy resin (EP), achieving multifunctionality in EP composites remains a significant challenge. Herein, a novel “structure–interface–function” design strategy is proposed. We report for the first time the preparation of DOPO-based hollow microspheres FADM through self-stabilized precipitation copolymerization of DOPO-containing monomer, divinylbenzene, and maleic anhydride. Benefiting from elaborate molecular design, FADM exhibited superior flame retardancy and excellent interfacial compatibility. By incorporating merely 4 wt% of FADM, the EP composites exhibited a limiting oxygen index of 34.9 % and successfully attained a UL-94 V-0 rating. Moreover, the EP/FADM composites exhibited a 22.6 % reduction in total heat release and a 36.0 % decrease in smoke production rate. Most importantly, the anhydride groups present on the surface of FADM actively participate in the curing process of EP resin, thus enhancing interfacial compatibility. The unique hollow structure endowed FADM with outstanding energy absorption capacity, resulting in a 50 % increase in impact strength of the EP/FADM composites through crack deflection mechanism. Furthermore, the EP/FADM composites exhibited low dielectric properties and good transparency due to well-dispersed FADM with hollow structure in EP matrix. This “structure–interface–function” strategy presents a new design concept to construct multifunctional EP systems with superior properties for electronic packaging and aerospace.