Renewable Cardanol-Based Star-Shaped Prepolymer Containing a Phosphazene Core as a Potential Biobased Green Fire-Retardant Coating

A novel star-shaped cardanol oligomer (HCPP) derived from cardanol and hexachlorocyclotriphosphazene was prepared, and its structure was identified using proton nuclear magnetic resonance (1H NMR, 13C NMR, 31P NMR) and Fourier transform infrared spectroscopy (FTIR) techniques. The HCPP underwent a thermal-initiated curing reaction both with and without catalyst. Oxygen was essential to this curing reaction, and the film preparation process was very simple. The curing reaction of HCPP was monitored by differential scanning calorimeter (DSC) and Fourier transform infrared (FTIR) methods. The catalyst (cobalt naphthenate) could remarkably improve the curing reaction speed. The cardanol-based cured films show excellent thermal stabilities. Interestingly, the char yield of the film cured at 800 °C in nitrogen is above 29%, implying that the fire-retardancy of cardanol-based polymers can be notably increased by in traducing a hard phosphazene core into the structure. Meanwhile, all cured films are highly transparent and have Tg values above 50 °C.