Synthesis and Thermal Behaviour of Novel Aliphatic/Aromatic Hepta-Cyclopentyl Bridged Polyhedral Oligomeric Silsesquioxanes (POSSs)/ Polystyrene (PS) Nanocomposites

The resistance to the thermal degradation of some Polystyrene (PS) based nanocomposites, containing as filler novel aliphatic and aromatic hepta-cyclopentyl bridged Polyhedral Oligomeric Silsesquioxanes (POSSs), was evaluated in both inert and oxidative atmospheres. The fillers were formed by two identical silicon cages R7(SiO1.5)8 (R = cyclopentyl) linked to several aliphatic [-(CH2)2-, -(CH2)6- and -(CH2)10-] and aromatic (Ar, Ar-Ar, Ar-O-Ar and Ar-S-Ar) bridges, where Ar = p-C6H4. Nanocomposites were prepared by in situ polymerization of styrene in the presence of 5% w/w of appropriate POSS. The actual filler content in the products obtained, checked by 1H NMR spectroscopy, resulted in all cases slightly higher than in starting mixtures. The glass transition temperature (Tg) was also determined by Differential Scanning Calorimetry. The degradation of nanocomposites was carried out into a thermobalance and the temperatures at 5% mass loss (T5%) were determined to evaluate the resistance to the thermal degradation which resulted, for the compounds here studied, higher not only than PS, but also than those of the nanocomposites filled with the corresponding hepta-isobutyl POSSs. The results were compared and discussed and suggested that the increments of resistance to thermal degradation in respect to neat PS (T5% of nanocomposite - T5% of PS) obey to an additivity group law.