A novel reactive flame retardant named hexakis (4-diethyl phosphate hydroxymethyl phenoxy) cyclotriphosphazene (HPHPCP) was synthesized from hexachlorocyclotriphosphazene (HCCP)

p-hydroxy benzaldehyde and diethyl phosphite. Chemical structures of intermediate and HPHPCP were characterized by Fourier-transform infrared spectroscopy (FTIR)

proton and 31P nuclear magnetic resonance (NMR). Thermal stability of the HPHPCP was determined via thermogravimetric analysis (TGA). Halogen-free flame-retardant rigid polyurethane foams (RPU) were prepared by using HPHPCP as a reactive flame retardant. The effect of HPHPCP content on the thermal and flame-retardant properties of RPU was investigated with TGA

and limiting oxygen index (LOI). The temperatures of 5%(mass) loss (T5%) of HPHPCP in nitrogen and air were 162.7℃ and 153.0℃

and the residues at 800℃ of HPHPCP in nitrogen and air were 42.1% and 12.0%(mass)

respectively. HPHPCP could enhance thermal stability of RPU. The T5% of RPU-20%HPHPCP was 193.9℃

20℃ higher than pure RPU. Moreover

limiting oxygen index (LOI) of RPU increased with increasing HPHPCP

and LOI of RPU-30%HPHPCP was 27%.