Construction of Polyethyleneimine/Boric Acid‐Functionalized Hollow Mesoporous Silica Toward Flame Retardancy and Mechanical Enhancement of DOPO‐Based Epoxy Resin

ABSTRACT The inherent flammability of epoxy resin (EP) has limited its widespread application in fields requiring high fire safety. Traditional halogen‐free flame‐retardant EP systems have failed to simultaneously achieve improvements in flame retardancy and mechanical properties. Moreover, they often disrupted the EP curing network. To address this issue, a polyethyleneimine/4‐formylphenylboronic acid–functionalized hollow mesoporous silica (FPSi) was prepared in this work. A series of flame‐retardant EP composites were then prepared by combining FPSi with DOPO. The results demonstrated that at a total loading of 5 wt%, the incorporation of FPSi into the DOPO‐containing EP system effectively repaired the crosslinking network damaged by DOPO. The glass transition temperature of EP composites was significantly recovered. The tensile and bending strengths were improved compared with neat EP. Meanwhile, all formulations maintained a UL‐94 V‐0 rating and a limiting oxygen index above 32%. Char residue analyses revealed that FPSi promoted the enrichment of silicon and boron elements in the char layer, forming a dense graphitized char structure. This enhanced condensed‐phase charring compensated for the loss of gas‐phase flame retardancy caused by the reduced DOPO content. This work provided an effective pathway for achieving simultaneous optimization of flame retardancy, mechanical properties and thermal resistance in EP.