Henry W. Milliman

The morphology and properties of melt-mixed polyoxymethylene/ monosilanolisobutyl-POSS composites

In this study, the morphology and thermo-mechanical behavior of composites formed by a polyoxymethylene (POM) matrix and monosilanolisobutyl polyhedral oligomeric silsesquioxane (msib-POSS) filler have been studied. The msib-POSS molecules were added to the POM by direct melt blending at loadings between 0 and 10 wt.%. Hydrogen bonding interactions were detected between POM and msib-POSS Si-OH groups, increasing their mutual compatibility and leading to nanometer-size dispersion of some msib-POSS molecules. These interactions do not prevent POSS aggregation during blending, but lead to micron-scale msib-POSS domains. The thermal decomposition temperature of the composites remained practically constant under inert and oxidative conditions. The low temperature thermal transition (γ) and glass transition temperature (Tg) of POM were found to move to higher temperatures only when 2.5 wt.% of msib-POSS was added, indicating that POSS is physically linked to the POM chains, restricting their motion under those conditions. Low content (2.5 wt.%) of msib-POSS results in antiplastization, whereas higher levels of POSS lead to a decrease in the storage modulus of the polymer. The relationships among these effects and the morphological characteristics of the systems will be discussed herein.

POSSⓇ in Tight Places

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.

Clay Aerogel Supported Palladium Nanoparticles as Catalysts

Highly porous, low density palladium nanoparticle/clay aerogel materials have been produced and demonstrated to possess significant catalytic activity for olefin hydrogenation and isomerization reactions at low/ambient pressures. This technology opens up a new route for the production of catalytic materials.