Thermodegradable polycarbonates: Effect of substituents on the degradation temperature

Y. Martele, V. Van Speybroeck, M. Waroquier, E. Schacht


The thermal degradation process of some new polycarbonates is investigated from an experimental and theoretical point of view, in order to obtain insight into the microscopic aspects that influence the reaction mechanism and the process of thermolysis. In particular, attention is focussed on the influence of the type of substituents in the polymer chain on the degradation temperature. A series of novel polycarbonates were designed differing from each other by the groups attached at the alpha and beta carbon atoms. Thermal behavior was characterized by thermogravimetrical analyses. The polymers undergo rapid and complete thermolysis at different degradation temperatures depending on the structure. The degradation products were separated by gas chromatography and analyzed by mass spectroscopy. The ratio of formed dienes in the product distribution depends on the heating rate. Furthermore, density functional theory calculations were performed on a series of model compound systems for the polycarbonates under study, in particular carbonate systems differing by the groups attached at the alpha and beta carbons. The study proves that the thermal degradation route can be controlled by tailoring the polymer backbone structure. Moreover, ab initio calculations provide further insight into the microscopic ingredients that govern the degradation process and associated reaction rates.