Enhancing flame retardancy and dielectric performance of epoxy resins through benzoxazine-phosphorus modification

A P/N-containing flame retardant, DOPOBH, was synthesized with salicylaldehyde, p-aminophenol, 9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide (DOPO) and formaldehyde. The performance of DOPOBH in flame retardant modification of 4,4′-diaminodiphenyl sulfone(DDS)/diglycidyl ether of bisphenol A (DGEBA, E−44) system was studied in terms of limiting oxygen index (LOI), vertical burning testing (UL-94) and cone calorimeter test (CCT). When the phosphorus content was 1.5 wt% of the whole system, DOPOBH modified epoxy resin (EP/P1.5) exhibited excellent flame retardancy (achieving a UL-94 V-0 rating and the LOI value of 35.2 %). Compared with pure EP, a 54.3 % decrease of peak heat release rate (PHRR) and ca. 5 times of residue (with an intumescent structure) was obtained with EP/P1.5 in CCT. Based on the results of CCT, scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and thermogravimetry-infrared spectroscopy (TG-IR), DOPOBH was verified to play important roles in both gas phase and solid phase. In addition, the addition of DOPOBH could improve the dielectric properties of epoxy resin and provide new strategies for high-performance applications in electronic packaging. [Display omitted] •Synthesis of a novel flame retardant, DOPOBH, incorporating P/N elements for enhanced fire resistance.•Successful modification of DDS/DGEBA epoxy system with DOPOBH, achieving UL-94 V-0 rating at 1.5 wt% phosphorus.•Remarkable flame retardancy demonstrated by a 54.3 % reduction in peak heat release rate (PHRR) and substantial residue formation.•Comprehensive analysis (CCT, SEM, TGA, TG-IR) confirms a dual flame retardant mechanism in both gas and solid phases.•DOPOBH enhances fire performance and improves dielectric properties, suggesting potential for electronic packaging applications.