Hepta isobutyl polyhedral oligomeric silsesquioxanes (hib-POSS)

Abstract

Six polyhedral oligomeric silsesquioxanes (POSSs) with general formula R7 R′1 (SiO1.5)8, where R- was an isobutyl group and R′- a variously substituted phenyl group, namely hepta isobutyl polyhedral oligomeric silsesquioxane (hib-POSS), were prepared and their composition was checked by elemental analysis and 1H NMR spectroscopy. The degradation of compounds obtained was studied by simultaneous differential thermal analysis/thermogravimetry (DTA/TG) technique, in both inert (flowing nitrogen) and oxidative (static air atmosphere) environments, in order to draw useful information about their thermal stability. Experiments, performed in the 35–700 °C temperature range, showed different behaviour between the two used atmospheres. The formation of volatile compounds only, with an about complete mass loss, was observed under nitrogen, while a solid residue (≈40–50% in every case), due to the formation of SiO2, as indicated by the FTIR spectra, was obtained in static air atmosphere. The results obtained were discussed and compared, and the classifications of resistance to thermal degradation in the studied environments were made. A comparison between the thermal stabilities of hib-POSSs and analogous cyclopentyl POSSs previously studied was also performed.