Dynamics of multifunctional polyhedral oligomeric silsesquioxane/ poly(propylene oxide) nanocomposites as studied by dielectric relaxation spectroscopy and dynamic mechanical spectroscopy

An investigation was carried out of the segmental and normal mode dynamics in multifunctional polyhedral oligomeric silsesquioxane (POSS)/poly(propylene oxide) (PPO) nanocomposites. Data were generated by broadband dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS) over a wide range of frequency and temperature. Neat PPO exhibits two relaxation processes: normal mode (α_n) and segmental mode (α). The two multifunctional POSS reagents utilized (octaglycidyldimethylsilyl-POSS and octaepoxycyclohexyldimethylsilyl-POSS) show a segmental process at lower frequency and a local relaxation at higher frequency. The POSS/PPO nanocomposites also show two relaxation processes (α_n and α), but interestingly, their time scale is shorter than in the corresponding neat PPO. Molecular origin and spectral characteristics of all relaxations are described. Comparison of DRS and DMS results revealed identical trends with respect to the POSS concentration, temperature, and the same time scale for the segmental and normal mode process. A detailed account of the effect of structure, concentration, and dispersion of POSS, molecular weight of PPO, and temperature on the molecular origin, temperature dependence, and spectral characteristics of relaxation processes in POSS/ PPO nanocomposites is provided.