Synthesis of Flame-retardant Phosphaphenanthrene Derivatives with High Phosphorus Contents

Two novel types of phosphate derivatives of phosphaphenanthrene with a high phosphorus content were prepared by phosphorylation reaction between either 2-(6-oxido-6H-dibenz oxaphosphorin-6-yl)-methanol (ODOPM) or 2-(6-oxido-6H-dibenz oxaphosphorin-6-yl)-1,4-benzenediol (ODOPB) and dialkyl phosphoryl chloride. The structures of all compounds were characterised by 1H NMR, 13C NMR, 31P NMR, Fourier transform infrared spectroscopy, and high-resolution mass spectrometry. The thermal stability of representative compounds was determined by thermal gravimetric analysis and differential scanning calorimetry. The results showed that the compounds have excellent resistance to oxidation, high thermal stability with an onset decomposition temperature above 200°C, and a high char yield over 25 %, owing to the high P content. The representative compound was added to conventional electrolytes of lithium-ion batteries as flame retardant additive, and the self-extinguishing time and ionic conductivity were measured. The result showed that the compounds have effective flame retardant properties.