Synthesis and thermal characterization of new dumbbell-shaped cyclopentyl-substituted POSSs linked by aliphatic and aromatic bridges

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Seven aliphatic and aromatic dumbbell-shaped bridged hepta-cyclopentyl polyhedral oligomeric silsesquioxanes (POSSs), in which two identical silicon cages R7(SiO1.5)8 (with R = cyclopentyl) are linked to various aliphatic [(CH2)n with n = 2, 6 and 10] and aromatic (Ar, Ar–Ar, Ar–O–Ar and Ar–S–Ar, where Ar = p-C6H4) bridges, were prepared through a literature method opportunely modified by us to obtain higher yields. The obtained products were checked by elemental analysis and 1 H NMR spectra, and the results were in very good agreement with those of expected products. The synthesized hepta-cyclopentyl POSSs were degraded, in dynamic heating conditions, in both flowing nitrogen and static air atmosphere. The determined temperatures at 5 % mass loss (T 5%) and residues at 700 °C evidenced a much better resistance to thermal degradation than the corresponding isobutyl POSSs we investigated in the past. For aromatic POSSs no substantial difference was found between the T 5% values in inert environment and those in oxidative atmosphere. By contrast the T 5% values of aliphatic POSSs in air were slightly lower than the corresponding ones in nitrogen and decreased, in both environments, on increasing the aliphatic chain length, then showing an opposite trend in respect of the corresponding isobutyl derivatives. This behaviour was interpreted as due to the presence in the POSSs molecules of bulky cyclopentyl groups in the place of smaller isobutyls.