Thermal decomposition of polyhedral oligomeric octaphenyl, octa(nitrophenyl), and octa(aminophenyl) silsesquioxanes

The mechanisms of the thermal degradation of polyhedral oligomeric octaphenylsilsesquioxane (OPS), octa(nitrophenyl)silsesquioxane (ONPS), and octa(aminophenyl)silsesquioxane (OAPS) were investigated. The -NO₂ or -NH₂ substituents on the phenyl group affected the mechanism of the POSS thermal degradation. The thermal stabilities of OPS, ONPS, and OAPS were characterized by TG and FTIR. Thermal degradation of OPS included mainly the degradation of caged polyhedral oligomeric silsesquioxane structures and phenyl groups. Nitro or amino substituents decreased its thermal stability. The thermal degradation processes of OPS, ONPS, and OAPS differed. Phenyl groups and cyclobutadiene were observed in the OPS degradation products. Oxygen radicals that caused intensive CO₂ release between 350 and 450 °C were generated by the degradation of ONPS -NO₂. OAPS released mainly aminophenyl groups at 370 °C, whereas a small number of phenyl groups decomposed at 500 °C. The OAPS reactivity could enhance the thermal stability of POSS structure in the polyimide OAPS composites.