A novel reactive flame retardant, (4-diethoxyphosphoryloxyphenoxy)(4-hydroxyphenoxy)cyclotriphosphazene (EPPZ), was prepared and characterized by FTIR P-31-NMR, and H-1-NMR analyses. Polyurethanes that contain (aliphatic phosphate) cyclotriphosphazene, with various phosphorus contents, were prepared from EPPZ, poly(propylene glycol), 1,4-butanediol, and 2,4-toluene diisocyanate. The polyurethanes were characterized by measurements of FTIR, TGA, DSC, limiting oxygen index (LOI), and tensile testing. The results indicated that the EPPZ-containing polyurethanes prepared in this study have higher glass-transition temperature, higher tensile strength, lower temperature of degradation, and higher char yield residues than those of the pure polyurethane. The activation energies at various degradation stages for the polyurethanes were calculated by Ozawa's method. The LOI of the EPPZ-containing polyurethane was increased with increasing EPPZ content and the polyurethanes showed flame-extinguishable behavior. Moreover, it was found that the effect of the flame retardancy of the polyurethanes took place primarily in the condensed phase. (C) 2003 Wiley Periodicals, Inc.