POSSⓇ in Tight Places

Abstract

The nature of polymer/POSS interactions and associated thermo-mechanical properties are discussed, and found to be consistent with small-molecule interactions associated with POSS, rather than a bottom-up selfassembly or any other method of classical reinforcement. Hansen solubility parameters are shown to accurately predict polymer/POSS combinations which are capable of successful interactions; such interactions are necessary, but insufficient for polymer property enhancement, since in many cases compatibility simply leads to plasticization by POSS. In the presence of stong additive/polymer interactions, such as via hydrogen bonding and/or π-π stacking, moduli, strength and glass transitions can all be increased, but only up to the solubility limit for the POSS in the polymer, which typically is reached at approximately 2.5-3 wt % POSS. Beyond the solubility limit, phase separation and rapid degradation of properties is observed.

Synthesis, thermal behavior, and kinetics of degradation of alkyl hepta cyclopentyl polyhedral oligomeric silsesquioxanes/polysterene nanocomposites

“…The largest increase of E a in static air atmosphere, for the two synthesized nanocomposites in respect to PS, confirms the active role of POSSs in the thermoxidative degradation process of the hybrid systems. In agreement with literature report, 24,25 the increase in POSS content, ranging between 3% and 5% w/w, enhances not only the resistance to the thermal degradation but, by slowing the degradation rate, the overall thermal stability of nanocomposites. If we compare these results with those obtained in the past for similar compounds, but characterized by an isobutyl 26 or phenyl 27 periphery (Table 6), we can affirm that the increase and the decrease, recorded in this work, both for the initial decomposition temperature and for the activation energy of degradation in respect to the use of isobutyl and phenyl POSSs, respectively, is derived from a double action dependent on the nature of the substituent groups and its compatibility with the polymer matrix:…”