Facile synthesis of P-functionalized diphenyl-methylvinyl-copolysiloxane for high-performance epoxy thermosets

The inherent brittleness and flammability of epoxy resin (EP) significantly limit its applications in high-performance fields. To address these challenges, a P-functionalized diphenyl-methylvinyl-copolysiloxane additive (DOPS) was synthesized via a simple method using diphenylsilane, dimethoxymethylvinylsilane, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). This additive was incorporated into epoxy systems cured with 4,4′-diaminodiphenylmethane (DDM), effectively enhancing both toughness and flame retardancy. When the DOPS content reached 6.93 wt%, the DOPS-4 thermosets achieved a V-0 rating in the UL-94 test. Additionally, the total heat release (THR) and total smoke production (TSP) of the DOPS-4 sample decreased by 41.34 % and 39.04 %, respectively, compared to the neat EP thermoset. These improvements were attributed to the trapping effect of P-containing radicals and the formation of a P/Si-containing char layer, which effectively inhibited combustion and reduced smoke and heat release. In addition, the flexural and impact strengths of DOPS-4 were improved by 15.6 % and 95.3 %, respectively, compared to the neat EP thermoset. These enhancements were ascribed to the rigid phosphaphenanthrene segments and abundant flexible chains in DOPS. Moreover, the DOPS-modified epoxy thermosets still exhibited excellent thermal stability. In sum, this work provides a facile and effective strategy to enhance the toughness and flame retardancy of epoxy thermosets, offering promising potential for advanced material applications.