The isothermal degradation of some polyetherketones: a comparative kinetic study between long-term and short-term experiments

The kinetics of the isothermal degradation of three high thermally stable aromatic polyetherketones was studied by both a long-term (about 3 years) experiment at a temperature (270 degreesC) largely lower than the temperatures of fusion, and a set of short-term experiments at temperatures near the temperatures of fusion. An induction period was observed at 270 degreesC, followed by two degradation stages, the first with an exponential increase of the weight loss rate (V) as a function of heating time (t) and the final one showing constant weight loss rate. Short-term experiments showed similar behaviour, but no induction period was observed. The equations V=V(o)x2(alphat) and V=K at various temperatures were determined for the exponential and linear degradation stages, respectively. The c-folding time alpha increased with temperature according to Arrhenius-type equations, by which the apparent activation energy values for degradation could be determined. The results are discussed and indicate that the kinetic parameters of degradation change with temperature. (C) 2002 Elsevier Science Ltd. All rights reserved.