Magnolol-based active ester modified cycloaliphatic epoxy resins with improved flame retardancy, dielectric and mechanical property

Cycloaliphatic epoxy resins exhibit excellent dielectric properties but are often harder to be flame retarded. To address this issue, a magnolol-derived active ester DDA was synthesized and employed to prepare flame-retardant cycloaliphatic epoxy resins through the intrinsic incorporation of a phosphaphenanthrene moiety (DOPO). Compared with anhydride MHHPA-cured resins, DDA demonstrated superior char-forming capability and enhanced the compactness of carbon residues. Under equivalent phosphorus loadings, the DDA-cured resin (CFDAP) exhibited a significantly higher limiting oxygen index (LOI) value of 30.2 %, notably surpassing the 26.7 % LOI of the MHHPA-cured counterpart. CFDAP effectively achieved reductions of 44 % in peak heat release rate and 50 % in total heat release during combustion. Importantly, ether bonds instead of ester bonds in the main chain of CFDAP enhanced the thermal stability and tensile strength relative to MHHPA-cured system. The chemical integration of DOPO moiety further improved the dielectric properties of epoxy resins at high frequencies by increasing free volume within the matrix. Collectively, the active ester curing agent DDA enables simultaneous enhancements in flame retardancy, thermal stability, mechanical properties, and dielectric performance of epoxy resins, presenting an efficient strategy for designing advanced electronic packaging materials suitable for high-frequency and high-speed electronic communication.