Prediction of lifetime of poly(2-hexyne) films through the kinetics of thermooxidative degradation from thermogravimetric and molecular weight data

Substituted polyacetylenes suffer from important degradation in contact with air at moderately high temperatures, making them useless since some mechanical properties are lost. To predict the lifetime a kinetic study of the thermooxidative degradation process for poly(2-hexyne) is presented. Thermogravimetry and GPC have been used to analyse some variables representative of polymer degradation, namely weight loss due to emission of volatiles, oxygen uptake and molecular weight evolution. The weight of the samples presented an initial increase (due to oxidation) followed by a quasi-linear decrease (due to volatilization). A mechanism considering both phenomena has been proposed and modelled, resulting in a kinetic equation which satisfies the whole degradation process. The evolution of weight loss has also been related to the chain scission, obtaining a linear dependence in agreement with the proposed degradation kinetic model. However, accurate quantification of oxygen uptake presented some problems so that this variable can only be considered as a qualitative indication of the degradation level.