Enthalpy relaxation of low molecular weight PMMA: a strategy to evaluate the Tool-Narayanaswamy-Moynihan model parameters

The enthalpy recovery mechanism of a low molecular weight synthesis of polymethylmethacrylate is investigated by means of differential scanning calorimetry (DSC) experiments. The experimental results can be described satisfactorily in terms of the Tool-Narayanaswamy-Moynihan theory. This work is mainly focused on developing a strategy for evaluation of the best set of parameters for the model. The approach starts with a simultaneous fitting procedure of several experimental DSC traces. Sets of parameters are obtained which exhibit agreement with experiments. The enthalpy lost on ageing of the sample in the glassy state as a function of the annealing time is then compared with the predictions provided by using the different sets of parameters. We show that this procedure is able to single out the best set of parameters and to provide a good estimation of the Adam-Gibbs temperature.