Silica oligomeric

Icopini, G.A., Brantley, S.L., Heaney, PJ. (2005). Kinetics of silica oligomerization and nanocolloid formation as a function of pH and ionic strength at 25°C. Geochimica et Cosmochimica Acta, 69, 293-303. 

Trinh TT, Jansen APJ, van Santen RA, Meijer EJ (2009) Role of water in silica oligomerization. J Phys Chem C 113 2647-2652. 

P.J. (2005) Kinetics of silica oligomerization and nanocolloid formation as a function of pH and ionic... 

Nanocomposite based on polyurethane (PU) is prepared using silica, clay, and Polyhedral Oligomeric Silsesquioxane (POSS). Preparation, characterization, mechanical and barrier properties, morphology, and effect of processing conditions have been reported on polyurethane-based nanocomposites [72,73]. 

To select the metal to be incorporated into the substrate porphyrin unit, the following basic properties of metalloporphyrins should be considered. The stability constant of MgPor is too small to achieve the usual oligomeric reactions and purification by silica gel chromatography. The starting material (Ru3(CO)i2) for Ru (CO)Por is expensive and the yield of the corresponding metalation reaction is low. Furthermore, the removal of rutheniirm is difficult, and it is likewise difficult to remove the template from the obtained ruthenium CPOs. Therefore, ZnPor is frequently used as a substrate in this template reaction, because of the low prices of zinc sources (zinc acetate and/or zinc chloride), the high yield in the metalation reaction, the sufficient chemical stability of the ZnPor under con-... 

The most spectacular results with temperature-programmed LC have been obtained for some notoriously difficult polymeric additives. Characterisation of the oligomeric HALS stabiliser poly [[6-[(l,l,3,3-te-tramethylbutyl) amino]-l,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidyl)imino]-l,6-hexanediyl [(2,2,6,6-tetramethyl-4-piperidyl)imino]] (I) (Figure 4.12) is difficult for several reasons it has a broad MWD, may contain isomers, and has several amino groups that promote almost irreversible adsorption to silica based column packings in LC. 

Fig. 3.3 The common two-stage sol-gel process used to entrap biopolymers in a silica matrix (see Scheme 3.1). The first stage serves to hydrolyze alkoxide Equation (2) in the acidic or alkaline media. This is also attended with condensation reactions Equations (3) and (4) resulting in the formation of oligomeric silica that self-organizes in the form of sol nanoparticles. Biopolymers are entrapped in the...

De Klerk, A. 2007. Effect of oxygenates on the oligomerization of Fischer-Tropsch olefins over amorphous silica-alumina. Energy Fuels 21 625-32. 

PDMS nanocomposites with layered mica-type silicates were also reported.374 A two-step sol-gel process of the in situ precipitation of silica led to the development of siloxane-based nanocomposites with particularly high transparencies.3 5 Some unusual nanocomposites prepared by threading polymer chains through zeolites, mesoporous silica, or silica nanotubes were reviewed.3 6 Poly(4-vinylpyridine) nanocross-linked by octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane was reported.377... 

Controlled hydrolysis of RSiX3 compounds gives so-called silsesquioxanes or POSS compounds (Polyhedral Oligomeric SilSesquioxane), which can be used as models for silica surfaces or supports for catalysts [4] (Figure 18.2, schematic structure on the right). 

D. Y. Zhao, Q. S. Huo, J. L. Feng, B. F. Chmelka, and G. D. Smcky, Nonionic triblock and star diblock copolymer and oligomeric surfactant syntheses of highly ordered, hydrothermally stable, mesoporous silica structures, J. Am. Chem. Soc. 120(24), 6024-6036 (1998). 

Oligomerization of 1-decene in the presence of a silica-BF3-H20 catalyst was shown to yield a mixture of di-, tri- and tetramers that gives a lubricant after hydro-genation. 

Traditionally, solid acidic catalysts are applied in industry for the oligomerization of butenes and are still studied. MTS-type aluminosilicates,522 a NiCsNaY zeolite,523 and a silica-alumina containing 13% alumina524 proved to be active and selective catalysts. Moreover, deactivation rates of these catalysts are also favorable. Sulfated zirconia promoted with Fe and Mn was active and selective to yield primarily dimethylbutene isomers under supercritical conditions.525 A small amount of water improved productivity and decreased deactivation. A study showed that the blending octane number of Cg hydrocarbons is directly linked to the number of allylic hydrogens in the molecules.526... 

Although tetraalkoxysilanes are usually applied as silica precursors in sol-gel procedures, the oligomeric type precursors can also be used instead. Ethyl silicate 40 (ES 40) is the most common commercial form of ethoxypolysiloxane available at prices competitive to those of TEOS/TMOS. Hence its application in the synthesis of composite adsorbents could be economically attractive provided that this would has little or no adverse effect on their final properties. The objective of this work was to test an alternative, cost-effective preparation procedure making use of the low-cost reagents ES 40 and 95wt% EtOH and to compare the properties of the adsorbents obtained with those of their counterparts similar in composition, yet synthesized with the use of TEOS. 

Figure 1 gives results obtained by Alexander et al. (I) and Baumann (2) by dissolving fine particles of commercially available vitreous silica powders in aqueous solutions. Similar data obtained in polymerization and depolymerization experiments by Scheel et al. (15) and Friedberg (10) indicate that the curve shown in Figure 1 represents an equilibrium concentration for oligomeric acid. It can be approached from the supersaturated state of monomeric silicic acid as well as from a solution of pure polymeric silicic acid. 

Oligomerization of an aminosilane coupling agent and its effects on the adhesion of thin polyimide films to silica... 

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