Kinetics of the Decomposition of Polyoxypropylene Glycols by Differential Scanning Calorimetry and Thermogravimetric Analysis

The thermal decomposition of polyoxypropylene glycols under a nitrogen atmosphere has been studied in the temperature range 320 to 700[ddot] K under dynamic operating conditions with a differential scanning calorimeter and a thermogravimetric scanning system. In the DSC studies, Ellerstein's suggestion to use stainless steel mesh was followed to minimize differential energy losses. Differential scanning calorimetry yields zero-order kinetics while the data obtained with the thermogravimetric system fits first-order kinetics. Various ways of decomposition, satisfying both zero- and first-order kinetics, are discussed. The heat of decomposition is found to change with temperature, and activation energies obtained by DTG increase with rate of heating. Differential enthalpic analyses provide activation energies applicable to chain ruptures as well as volatile product evaporation, whereas thermogravimetric analyses furnish activation energies only for the second stage.