Heat stability and degradation of thermally stable prepolymers in a controlled atmosphere - II: Heat stability and degradation of acetylene-chromene terminated prepolymers

The heat stability and thermal degradation of two acetylene-chromene termin ated polymers, called polyA (polymer of 6,6'-isopropyl dichroman) and polyF (polymer of 6,6'-hexafluoroisopropyl dichroman) were investigated in contr olled 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 analy sis (TGA). Both polymers degraded starting at 350 degreesC, according to a single mechanism for polyA and two distinct mechanisms for polyF. In additi on, the isothermal TGA study of thermal ageing for 24 hours showed that bot h compounds were very stable at 250 degreesC (losses of mass less than 3%) and that polyF was more stable than polyA when heated between 350 and 550 d egreesC. Degradation residues were analyzed by infrared-Fourier transform spectrosco py (FT-IR). Volatile organic compounds (VOC) released by pyrolysis were ana lyzed by pyrolysis/thermal desorption cold trap/gas chromatography/mass spe ctrometry. These methods enabled us to determine degradation mechanisms in the same temperature interval. The data showed that the major part of the d egradation occurred in the cyclic ether, with breaks at cross-linking nodes and C-O bonds. Since the skeletons of the crosslinking nodes of both compo unds were identical, the higher stability can be attributed to the presence of fluorine in its central hexafluorinated pivot, providing greater heat s tability than the isopropyl pivot in polyA.