Heat Stability and Degradation of Thermally Stable Prepolymers in a Controlled Atmosphere
The heat stability and thermal degradation of two acetylene-chromene terminated polymers, called polyA (polymer of 6,6′-isopropyl dichroman) and polyF (polymer of 6,6′-hexafluoroisopropyl dichroman) were investigated in controlled conditions. The environmental impact of their degradation was studied in order to predict their remediation and fate after use. Degradation of the polymers was followed by dynamic thermogravimetric analysis (TGA). Both polymers degraded starting at 350°C, according to a single mechanism for polyA and two distinct mechanisms for polyF. In addition, the isothermal TGA study of thermal ageing for 24 hours showed that both compounds were very stable at 250°C (losses of mass less than 3%) and that polyF was more stable than polyA when heated between 350 and 550°C. Degradation residues were analyzed by infrared-Fourier transform spectroscopy (FT-IR). Volatile organic compounds (VOC) released by pyrolysis were analyzed by pyrolysis/thermal desorption cold trap/gas chromatography/mass spectrometry. These methods enabled us to determine degradation mechanisms in the same temperature interval. The data showed that the major part of the degradation occurred in the cyclic ether, with breaks at cross-linking nodes and C–O bonds. Since the skeletons of the cross-linking nodes of both compounds were identical, the higher stability can be attributed to the presence of fluorine in its central hexafluorinated pivot, providing greater heat stability than the isopropyl pivot in polyA.