Glycidyl ether-terminated branched polysiloxane and its synergy with DOPO for the preparation of flame-retardant, high-strength, and high-toughness epoxy resin

• Synthesized glycidyl ether-ended branched PDMS and DOPO-modified epoxy resins. • PDMS-GE and DOPO enhanced mechanical properties by 21.1% and 32.5%. • Achieved UL-94 V-0 and LOI of 37.5 via PDMS-GE/DOPO flame-retardant synergy. • Optimized hydrophobicity and low dielectric properties for electronics. To develop flame-retardant epoxy resin (EP) with high strength and toughness, a series of glycidyl ether-terminated polydimethylsiloxanes (PDMS-GEs) with varying branching degrees were synthesized. These PDMS-GEs, along with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), were utilized to modify a diglycidyl ether of bisphenol A/diaminodiphenylmethane (DGEBA/DDM) epoxy system. This approach successfully yielded hydrophobic, low-dielectric EP composites exhibiting excellent integrated mechanical and flame-retardant properties. Characterization of mechanical and thermal properties revealed that both the branching degree of PDMS-GE and the incorporation of DOPO positively impacted the material's strength and toughness. The EP composite (EP/H-GE/DOPO) co-modified with hyper-branched PDMS-GE (H-GE), and DOPO demonstrated optimal mechanical performance. Compared to neat EP, this composite exhibited increases of 11.3% in tensile strength, 21.1% in flexural strength, and 32.5% in impact strength. Furthermore, the EP/H-GE/DOPO composite established an effective P/N/Si synergistic flame-retardant system. It achieved a UL-94 V-0 rating and possessed a high limiting oxygen index (LOI) of 37.5. Compared to neat EP, cone calorimetry tests (CCT) indicated significant fire safety improvements with a char residue increased by 142.9%, the peak heat release rate (PHRR) and total heat release (THR) decreased by 38.2% and 30.3%, respectively. Additionally, the total yields of CO and CO 2 were reduced by 35.3%.