Organic Tethers Research Articles

Synthesis and characterization of organic–inorganic hybrid polymers with a well‐defined structure from diamines and epoxy‐functionalized polyhedral oligomeric silsesquioxanes

AbstractA new class of organic‐inorganic hybrid polymers with well‐defined structure was prepared by reacting diepoxyhexavinyl polyhedral oligomeric silsesquioxanes (DehvPOSS) with diamines of different chain lengths. The structures and properties of these hybrid polymers were well characterized by FTIR, 29Si‐NMR, GC‐MS, and TGA. A modeling characterization was employed to help identify the structures of organic tethers linked between the POSS cages. The results indicated that at the stoichiometric ratio of DehvPOSS to diamine, well‐defined organic–inorganic hybrid polymers with controlled variation of the organic tether architecture can be made, and each organic tether connected four POSS cages. Thermal stability (Tdec) increased with an increase in the tether length of the diamine molecules, and the highest Tdec was obtained with butanediamine (rather than propanediamine or ethanediamine) as the organic tether. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3730–3735, 2006

Self-assembled morphologies of monotethered polyhedral oligomeric silsesquioxane nanocubes from computer simulation

Self-assembly of functionalized nanoscale building blocks is a promising strategy for "bottom-up" materials design. Recent experiments have demonstrated that the self-assembly of polyhedral oligomeric silsesquioxane (POSS) "nanocubes" functionalized with organic tethers can be utilized to synthesize novel materials with highly ordered, complex nanostructures. We have performed molecular simulations for a simplified model of monotethered POSS nanocubes to investigate systematically how the parameters that control the assembly process and the resulting equilibrium structures, including concentration, temperature, tether lengths, and solvent conditions, can be manipulated to achieve useful structures via self-assembly. We report conventional lamellar and cylindrical structures that are typically found in block copolymer and surfactant systems, including a thermotropic order-order transition, but with interesting stabilization of the lamellar phase caused by the bulkiness and cubic geometry of the POSS nanocubes.

Organically-Modified Silica Xerogels for Adsorption of CH4 at 298 K

Organic tethers have been incorporated into acid- and base-catalysed silica sol–gels. The surface area is modified by this insertion suggesting an interaction at a molecular level. The HCl-catalysed SiO2 sol–gel had its relative extent of adsorption at 298 K of CH4 relative to H2O: (i) depressed by the addition of 5% bis(triethoxysilyl)methane (ii) increased by the addition of 5% bis(trimethoxysilyl)hexane which attributed the tether hydrophilic-lipophilic balance (HLB). The reasons for this unexpected physical adsorption of CH4 at a temperature far above its boiling point are now being explored, along with the potential of these materials for selective hydrocarbon sensors and separators.

Organic/Inorganic Imide Nanocomposites from Aminophenylsilsesquioxanes

We present here part of an ongoing study on structure−processing−property relationships in cubic silsesquioxane (cube) nanocomposites. Here, we focus on imide nanocomposites prepared from octaaminophenylsilsesquioxane (OAPS) as a model nanobuilding block for rigid, high-temperature hybrid nanocomposite materials. OAPS units are linked NH2 vertex to NH2 vertex by reaction with various dianhydrides to form three-dimensional nanocomposites. The architecture of the organic tethers between vertices can be manipulated to optimize processability, rigidity, and thermomechanical properties. Studies were initiated using an extreme tether structure with zero flexibility prepared by solvent casting and then curing mixtures of OAPS with pyromellitic dianhydride (PMDA) at 330 °C. The resulting materials are extremely brittle, making thermomechanical property measurements quite difficult. Tether rigidity, length, and cross-link densities were then modified using reactions of OAPS with oxydiphthalic anhydride (ODPA) and diluting with oxydianiline (ODA) to adjust nanocomposite stiffness. FTIR and DMA of the OAPS/ODPA/ODA nanocomposites suggest that cure temperatures of >500 °C are necessary for optimal imidization. However, increasing the cross-link density alone by increasing OAPS loading without curing at high temperatures also significantly improves thermomechanical stabilities. DMA, TGA, and nanoindentation measurements show that macroscopic relaxation is eliminated completely at OAPS loadings of >60 mol % providing 5% mass loss at temperatures >570 °C and compressive moduli of ≈3.8 GPa.

Organic/Inorganic Hybrid Composites from Cubic Silsesquioxanes. Epoxy Resins of Octa(dimethylsiloxyethylcyclohexylepoxide) Silsesquioxane

Standard research protocols were developed to explore the use of octahedral silsesquioxane (cube) organic/inorganic nanocomposites as model systems for determining nanostructure−processing−property relationships to demonstrate that nanoscale structural manipulation of the organic component can significantly change macroscale physical properties. Comparison of octaglycidyldimethylsiloxyoctasilsesquioxane [(glycidyl-Me2SiOSiO1.5)8] (OG)/diaminodiphenylmethane (DDM) and octa(ethylcyclohexylepoxide)dimethylsiloxy silsesquioxane (OC)/DDM nanocomposite resins provide the first demonstration that well-defined nanostructures can be formed wherein linear organic tethers of known structure join only two cube vertices. HF dissolution of cubes followed by GPC analysis demonstrates that only linear tethers form in OC/DDM. TEM studies suggest that these nanocomposites are homogeneous at the nanometer scale, thus supporting the chemical analysis studies. The physical properties of these nanocomposites were then systemat...

A Polyimide Nanocomposite from Octa(aminophenyl)silsesquioxane

Octaaminophenylsilsesquioxane (OAPS) can serve as a nanosized building block for the construction of materials with nanometer control of the periodicity of the organic and inorganic components and bonding between components. We describe here the synthesis of a prototypical three-dimensional polyimide by reaction of OAPS with pyromellitic dianhydride (PMDA). Model studies with phthalic anhydride provided useful cure conditions. Thus, stoichiometrically correct OAPS/PMDA nanocomposites were obtained following curing of NMP and DMF reaction solutions at lower temperatures and then to >350 °C/N2 under vacuum. The resulting materials offer thermal stabilities in air and N2 of >500 °C (5% mass loss temperature) and char yields >75%/N2. X-ray powder patterns indicate that the resulting materials are completely amorphous, as might be expected from the extreme rigidity of the organic tethers linking cube vertexes that will prevent long-range ordering from occurring during curing. These materials hold promise for h...

Organic–Inorganic Nanocomposites with Completely Defined Interfacial Interactions

Access to structure–processing property relationships in nanocomposites is given through the work undertaken by these authors. Their approach relies on linking cubic silsesquioxane (see Figure) by organic tethers. The analytical data presented here form strong foundations for the formation of nanocomposites with well-defined interfaces and periodicity.