Oligomeric Brominated Flame Retardants: Synthesis and Synergistic Improvement in Flame Retardancy, Mechanical Properties, and Migration Resistance of Epoxy Resins

ABSTRACT Epoxy resins (EPs) have gained increasing attention due to their excellent properties, but endowing EPs with high mechanical properties and migration resistance while maintaining flame retardancy remains a challenge. This study addresses this challenge by developing novel oligomeric flame retardants (PB‐O and PB‐E), synthesized via a Heck cross‐coupling reaction of polybutadiene (PB) with decabromodiphenyl oxide (DBDPO) or decabromodiphenyl ethane (DBDPE). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) show these additives reduce EP curing temperatures and enhance char formation at elevated temperatures. UL‐94 and microscale combustion calorimetry (MCC) tests confirm exceptional flame retardancy: composites with 5 phr PB‐O/PB‐E achieve V‐1/V‐0 ratings (vs. pure EP), with peak heat release rates (PHRR) reduced by 40.3%/40.0% for enhancing fire safety. Synergistic rigid‐flexible effects (phenyl groups and PB chains) endow composites with outstanding mechanical properties: impact strength increases by 557% (PB‐O)/524% (PB‐E), flexural strength rises by 51.5%/49.2% versus unmodified EP. Migration rates of 5 phr PB‐O/PB‐E in EP composites show 0 after 84 h (5 phr PB@DBDPO/PB@DBDPE: 4.2%/4.0%) by migration tests. Hence, this work provides an integrated strategy to develop multifunctional oligomeric brominated flame retardants for EPs, which simultaneously improve flame retardancy, mechanical properties, and migration resistance to align with increasingly rigorous industrial requirements.