10.9 Prediction of Kinetic Behaviour

An important practical aspect of kinetic studies is the prediction of kinetic behaviour under conditions other than those used in the original experimental measurements ^[86], for example, the estimation of shelf-lives of drugs under normal storage conditions, from accelerated tests at higher temperatures. For predictions to be reasonably reliable, the values of the kinetic parameters, E, A and the forms of the conversion functions, f( ?) (or g( ?)), should not vary with T. The precision of the estimates of E and A also needs to be known ^[87]. Vyazovkin and Linert ^[87] and Maciejewski ^[60] have described some of the implications of attempting to predict kinetic behaviour when the kinetic model g( ?) or f( ?) has been incorrectly chosen (such as when non-unique kinetic triplets have been determined by single heating-rate experiments), and when the reactions are complex.

Flynn ^[88] has reviewed the prediction of service lifetimes of polymeric materials, at lower temperatures, from decomposition parameters obtained at relatively high temperatures. Reasons for the failure of predictions are discussed. These include extrapolation beyond temperatures at which phase changes (and accompanying changes of physical properties) occur.