Phenyl hepta cyclopentyl-polyhedral oligomeric silsesquioxane (ph,hcp-POSS)/Polystyrene (PS) nanocomposites: the influence of substituents in the phenyl group on the thermal stability

Some new Polystyrene (PS) nanocomposites were prepared by using two Polyhedral Oligomeric Silsesquioxanes (POSSs), namely RR'(7)(SiO1.5)(8) (where R = 4-methoxyphenyl or 2,4-difluorophenyl and R' = cyclopentyl), as fillers, and their degradation was studied to investigate the effect of the electron-donor or electron-withdrawing character of the phenyl group substituents on thermal stability. Nanocomposites were synthesized by in situ polymerization of styrene in the presence of various concentrations of POSS. Proton nuclear magnetic resonance (H-1 NMR) spectra indicated that the POSS content in the obtained nanocomposites was higher than that in reactant mixtures. Inherent viscosity (eta(inh)) and glass transition temperature (T-g) determinations indicated that the average molar mass of polymer in 4-methoxynanocomposites was the same than neat PS, while it was much lower in 2,4-difluoro derivatives. Degradations were carried out in both flowing nitrogen and static air atmospheres, in the scanning mode, at various heating rates, and temperature at 5% mass loss (T-5%) and the activation energy (E-a) of degradation of various nanocomposites were determined. The values obtained for 4-methoxyderivatives were higher than unfilled PS thus indicating higher thermal stability. Conversely, the values found for 2,4-difluoro derivatives were lower, in some cases even than those of neat PS. The results were discussed and interpreted.