THERMOOXIDATIVE DEGRADATION OF PHOSPHORUS-CONTAINING POLYURETHANE

The thermo-oxidative degradation of phosphorus-containing polyurethane (PU) incorporating phenylbis(hydroxyethyl)phosphonate was studied by using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) in oxidizing (air) atmospheres. From the resulting data apparent activation energies (E(a)) were obtained following the methods of Flynn, Broido and Ozawa. The activation energy of the first 10% conversion (alpha) evaluated from a single heating rate (Flynn's and Broido's) method is fairly constant, about 120 and 105 kJ/mol for common polyurethane and phosphorus-containing copolyurethanes, respectively. The Ozawa method, based on multiple heating rates, is used to evaluate the activation energy at high conversion. It is shown that the average activation energy (129-137 kJ/mol) for the first 30% conversion in air of the phosphorus-containing copolyurethane decreases with increase in phosphorus content, and E(a) (alpha = 0.4) and E(a) (alpha = 0.5) of the copolyurethanes are greater than that of polyurethane. This greater activation energy may be rationalized on the basis of the formation of thermally stable structures.