Poly(phosphorus-silicon-alkyne): Widening the application potential in epoxy resin with excellent flame retardancy, mechanical property, and unimpaired thermal stability

Aimed at promoting the flame retardancy of epoxy resin (EP) and widening its applications, a novel flame retardant, poly(phosphorus-silicon-alkyne) (PPSA), is synthesized from poly(silicon-alkyne) and 9,10-dihydro-9-oxa-10-phenanthroline-10-oxide (DOPO) to modify EP. The structure of PPSA is characterized by Fourier transform infrared and 1 H nuclear magnetic resonance. The PPSA introduction into EP significantly improves its chemical and physical properties. When containing 2.5–10 phr of PPSA, the modified EP achieve better flame resistance capability than neat EP. In particular, EP/PPSA-5.0 reaches a limiting oxygen index value of 31.2% and passes vertical burning test (UL-94) V-0 rating at the same time. The total heat release and total smoke production are lowered by 31.1% and 24.9%, respectively. In addition, the initial decomposition temperature ( T 5% ) of the modified EP is basically unchanged thanks to good stability of PPSA. Characterization of char residues generated in the combustion of EP/PPSA reveals that PPSA protects the EP from fire by diluting flammable gas with phosphorus free radicals and forming compact thermal stable layer containing silicon and phosphorus. Subsequently, measurements of mechanical properties show that impact strength and flexural strength are markedly improved by PPSA incorporation. Therefore, PPSA modifies EP to obtain excellent thermal stability and mechanical properties, justifying an outstanding flame retardant with comprehensive properties.