Brent D. Viers

Physical gelation in ethylene–propylene copolymer melts induced by polyhedral oligomeric silsesquioxane (POSS) molecules

The rheological behavior of ethylene–propylene (EP) copolymers containing polyhedral oligomeric silsesquioxane (POSS) molecules was investigated by means of wide-angle X-ray diffraction (WAXD), oscillatory shear, stress and strain controlled rheology in the molten state and dynamic mechanical analysis (DMA) in the solid state. WAXD results showed that the majority of POSS molecules in the EP melt were present in the crystal form. Oscillatory shear results showed that the EP/POSS nanocomposites exhibited a solid-like rheological behavior compared with the liquid-like rheological behavior in the neat resin, i.e. POSS caused physical gelation in EP. While POSS exhibited only a minimum effect on the flow activation energy of EP, the high POSS concentration samples were found to induce higher yield stress than the neat resin. This behavior was similar to the Bingham rheology, indicative of a structured fluid. DMA results indicated that the presence of POSS increased the Youngs modulus as well as the Tg of the EP copolymer. These results suggested that two types of interactions contributed to the physical gelation in EP/POSS melts were present: the strong particle-to-particle interactions between the POSS crystals and the weak particle-to-matrix interactions between the POSS crystals and the EP matrix.

Fluorinated Polyhedral Oligomeric Silsesquioxanes (F-POSS)†

Abstract : Partical contents: Hybrid Inorganic/Organic Polymers, Anatomy of a POSS Nanostructure, Poss Synthesis, FluoroPOSS Synthesis, Fluoropropyl(nTn), Fluorodecyl(8T8), Contact Angle of Water on Fluorodecyl POSS Surface, Contact Angle of Mercury on Fluorodecyl POSS Surface, AFM Image of Spin-Cast Fluorodecyl(8T8) Surface, Surface Energy of Fluorosiloxanes, Contact Angle and Chain Length, POSS Polymer Incorporation, Importance of R groups: Affect compatibility with polymer matrix, PVDF/Fluoroocytl(8T8) POSS,PVDF/Fluoroocytl(nTn) POSS, Fluorinated Ethylene/Propylene, Poly(chlorotrifluoroethylene), Amorphous FEP, Water Contact Angle.

Polyhedral Oligomeric Silsesquioxane (POSS) Styrene Macromers

Four polyhedral oligomeric silsesquioxane (POSS) macromers, R7Si8O12styrene (R=isobutyl, cyclopentyl, cyclohexyl, or phenyl), containing a single polymerizable styrene unit were synthesized from the POSS-trisilanols R7Si7O9(OH)3 in a high yield and purity. The base-assisted reaction to produce these macromers appears to be general for POSS-trisilanols of this type. However, in some cases it may be necessary to control the rate at which the base is introduced during reaction to prevent unwanted side reactions that decompose the trisilanol. Cyclohexyl-, cyclopentyl-, and isobutyl-substituted POSS-stryenes (at 30 wt% or approximately 4 mol% loadings) undergo free radical bulk polymerizations with styrene to produce polymers that show variation in the modulus above the glass transition temperature. The phenylPOSS derivative is too insoluble in styrene to undergo this polymerization. The effect on the modulus is more pronounced for the copolymers containing 30 wt% cycloalkylPOSS than that seen with isobutylPOSS, which is similar to that for bulk polymerized polystyrene. The effect of the group at the POSS cage on bulk polymer properties has been noted before and is presumed to arise from differences in polymer microstructure.

Nanocomposite Polyurethane Foams Via POSS Blends

Polyhedral Oligomeric Silsequioxane molecules have been incorporated into a commercial polyurethane formulation to produce nanocomposite polyurethane foam. This tiny POSS silica molecule has been used successfully to enhance the performance of polymer systems using co-polymerization and blend strategies. In our investigation, we chose a high-temperature MDI Polyurethane resin foam currently used in military development projects. For the nanofiller, or “blend”, Cp 7 T 7 (OH) 3 POSS was chosen. Structural characterization was accomplished by TEM and SEM to determine POSS dispersion and cell morphology, respectively. Thermal behavior was investigated by TGA. Two methods of TEM sample preparation were employed, Focused Ion Beam and Ultramicrotomy (room temperature).