Studies on the thermal stability of F- and non-F-containing ladder polyepoxysilsesquioxanes by TGA-FTIR

The thermal stability of non-F- (LPS-I) and F- (LPS-II) containing ladder polyepoxysilsesquioxanes under air and nitrogen was studied by DSC, TGA and TGA-FTIR techniques. The thermally curing temperature for LPS-II is about 20°C higher than that for LPS-I. Both LPS-I and LPS-II exhibits higher thermal stability under air and nitrogen as observed from TGA, where the decomposition temperatures at 5 and 10% weight loss were above 425 and 480°C, respectively. Under nitrogen, the higher decomposition temperature and residue from TGA was attributed to the gradual cleavage of C-Si and C-C bonds and high stability of F-containing side-chains (non-broken). Because of the weight gain from the oxidation of silsesquioxanes (RSiO_3/2) to silica (SiO₂), and gradual cleavage of F-containing side-chains, LPS-II exhibits higher decomposition temperature under air environment than under nitrogen. These phenomena detected from TGA could be observed directly from TGA-FTIR stack plots. As combined techniques for the evolved gas analysis, TGA-FTIR played an important role in explaining the phenomena of degradation related to the change of polymer chain structures during heating.