Synthesis and thermal behaviour of phenyl-substituted POSSs linked by aliphatic and aromatic bridges

Five novel bridged heptaphenyl polyhedral oligomeric silsesquioxanes (POSSs), in which two identical silicon cages R 7 (SiO 1.5 ) 8 (with R = Phenyl) are linked to various aliphatic [(CH 2 ) n with n = 2, 6 and 10] and aromatic (Ar–Ar and Ar–O–Ar, where Ar = p-C 6 H 4 ) bridges, were synthesized. The obtained compounds were characterized by elemental analysis and 1 H NMR spectroscopy, and the results were in very good agreement with those of expected products. The synthesized heptaphenyl POSSs were thermally degraded, in dynamic heating conditions (25–700 °C), in both flowing nitrogen and static air atmosphere. The temperatures at 5% mass loss ( T 5% ) and residues at 700 °C were thus determined to evaluate their resistance to thermal degradation, but no substantial difference was found between the values in the two studied environments. The obtained T 5% values were much higher than those of the corresponding isobutyl and cyclopentyl POSSs we investigated in the past. Also, the T 5% values of the phenyl POSSs with aliphatic bridges decreased quite linearly on increasing the number of bridge carbon atoms ( n C ). This behaviour was interpreted and attributed to the presence of the external corona formed by voluminous phenyl groups. The residue at 700 °C, which was largely higher than those of the corresponding isobutyl and cyclopentyl POSSs, was a further confirmation of the better thermal stability of the compounds here studied.