Novel phosphorus–silicon synergistic flame retardants: Synthesis and characterization

Three novel flame retardants containing both phosphorus and silicon elements in their structures, including [(1,1,3,3-tetramethyl-1,3-disiloxanediyl)di-2, 1-ethanediyl]bis(diphenylphosphine oxide) (FR-1), [(2,4,6,8-tetramethylcyclotetra-siloxane-2,4,6,8-tetrayl)tetra-2,1-ethanediyl]tetrakis[diphenylphosphine oxide] (FR-2) and 1,3,5,7,9,11,13,15-octakis(di-phenylphosphine oxide-2,1-ethanediyl)pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (FR-3) were synthesized by a convenient pathway from the reaction of diphenylphosphine oxide (DPPO) and vinyl-terminated siloxanes under the catalysis of triethylborane. The chemical structures of the target compounds were confirmed by nuclear magnetic resonance (1H NMR, 13C NMR, 29Si NMR and 31P NMR), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and Fourier transform infrared (FT IR) measurements. Thermogravimetric analysis (TGA) results indicated that the new flame retardants possessed good thermal stability both in nitrogen and in air. FR-3 containing polyhedral oligosilsesquioxanes (POSS) moiety exhibited the best thermal properties with a 10% weight loss temperature >400 °C and a residual weight ratio >39% at 700 °C.