Synthesis and characterization of new dumbbell-shaped isobutyl-substituted POSSs linked by aliphatic and aromatic bridges.

Six new dumbbell-shaped polyhedral oligomeric silsesquioxanes (POSSs), in which two identical silicon cages are linked to various aliphatic and aromatic bridges, were prepared by corner capping reaction between hepta isobutyltricycloheptasiloxane trisilanol (HIBT) and suitable bis(triethoxysilyl) derivatives. The products obtained were characterized by elemental analysis, 1H NMR and FTIR spectroscopy, thermogravimetric analysis. Degradations were carried out in flowing nitrogen and in static air atmosphere, and temperatures at 5% mass loss (T5%) and residues at 700°C were determined to investigate the resistance to the thermal degradation. The results obtained for various dumbbell-shaped POSSs were discussed and compared with each other. A comparison with the results previously obtained with the corresponding un-bridged phenyl, hepta isobutyl-POSSs showed a higher resistance to the thermal degradation of bridged POSSs