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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 self-assembly 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.