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

Five new dumbbell-shaped polyhedral oligomericsilsesquioxanes (POSSs), in which two identical siliconcages R7(SiO1.5)8 (with R = isobutyl), linked to variousaromatic bridges (Ar, Ar–Ar, Ar–O–Ar, Ar–S–Ar and Ar–SO2–Ar, where Ar = p-C6H4) were prepared through a literaturemethod opportunely modified by us to make easierpreparation and increase yield, which was higher than 70 %in all cases. The obtained products were the expected ones, assupported by the results of elemental analysis and 1H NMRspectra. Their resistance to the thermal degradation in bothflowing nitrogen and static air atmosphere was checked bydegrading samples at 10 C min-1 and determining temperaturesat 5 %mass loss (T5%) and residues at 700 C. TheT5% values in air were lower than the corresponding ones innitrogen, but the trend among the various POSSs investigatedwas the same in both used atmospheres, with the mosthigh value for the compound having the Ar–O–Ar aromaticbridge. The residues at 700 C in air of the compoundshaving not hetero-atoms (O or S) in the aromatic bridge werehigher than those in nitrogen, whilst no substantial differencewas observed for the other ones.