Thermal degradation and kinetics of polyethersulfone (PES) chips were studied in air, nitrogen, helium, and argon from room temperature to 790degreesC by high-resolution thermogravimetry (TG) at a variable heating rate in response to changes in the sample's degradation rate. In the four atmospheres, a two-step degradation process in air, argon, and helium or a three-step degradation process in nitrogen of the PES were found in this investigation. In particular, the three-step degradation process in nitrogen of the PES revealed by the high-resolution TG was hardly ever observed by a traditional TG. The initial thermal degradation temperature of the PES increases with the testing atmosphere in the following order: air < argon < helium < nitrogen but the activation energy of the first major degradation of PES increases in a different order: argon < nitrogen < helium < air. The degradation temperature, the temperature at the maximum weight-loss rate, the maximum weight-loss rate [(dalpha/dT)(m1) and (dalpha/dT)(m2)], char yield at 790degreesC, and activation energy of the first major degradation process obtained by the high-resolution TG were compared with those by traditional TG. The PES exhibits the largest (dalpha/dT)(m1) and the greatest char yield at 790degreesC in helium but the largest (dalpha/dT)(m2) and smallest char yield in air. A significant dependency of the thermal decomposition of the polymers on the physicochemical properties (density, thermal conductivity, and oxidative ability) of the testing atmospheres is elaborated for the first time. (C) 2003 Wiley Periodicals, Inc.