Synthesis, characterization and thermal stability of new dumbbell-shaped isobutyl-substituted POSSs linked by aromatic bridges

Five new dumbbell-shaped polyhedral oligomeric silsesquioxanes (POSSs), in which two identical silicon cages R-7(SiO1.5)(8) (with R = isobutyl), linked to various aromatic bridges (Ar, Ar-Ar, Ar-O-Ar, Ar-S-Ar and Ar-SO2-Ar, where Ar = p-C6H4) were prepared through a literature method opportunely modified by us to make easier preparation and increase yield, which was higher than 70 % in all cases. The obtained products were the expected ones, as supported by the results of elemental analysis and H-1 NMR spectra. Their resistance to the thermal degradation in both flowing nitrogen and static air atmosphere was checked by degrading samples at 10 A degrees C min(-1) and determining temperatures at 5 % mass loss (T (5%)) and residues at 700 A degrees C. The T (5%) values in air were lower than the corresponding ones in nitrogen, but the trend among the various POSSs investigated was the same in both used atmospheres, with the most high value for the compound having the Ar-O-Ar aromatic bridge. The residues at 700 A degrees C in air of the compounds having not hetero-atoms (O or S) in the aromatic bridge were higher than those in nitrogen, whilst no substantial difference was observed for the other ones.