Thermal degradation behavior and flammability of polyurethanes blended with poly(bispropoxyphosphazene)

Polyurethanes containing different amount of flame retardant, poly(bispropo xyphosphazene), were synthesized by a two-step polymerization. The thermal degradation behaviors of these polyurethanes were then studied by the therm al gravimetric analysis (TGA), TGA coupled with Fourier transform infrared analysis and elemental analysis. A limiting oxygen index was used to evalua te the flammability of these polyurethanes. For these modified polyurethane s under nitrogen, a two-stage thermal degradation behavior was observed. Th e first stage was caused by the degradation of hard segments, whereas the s oft segments were responsible for the second-stage degradation. The thermal degradation activation energies were calculated by using Ozawa's method. I t was found that the addition of flame retardant caused a decrease of the a ctivation energy in the first stage, but an increase in the second stage, w hich was probably due to the formation of a thermal stable structure. As fo r the flame retardancy, the modified polyurethanes have a higher char yield at 550 degrees C, and a higher limiting oxygen index than the neat polyure thane. (C) 1999 Elsevier Science Ltd. All rights reserved.