Molecular silica sols synthesis

Ihe literature " describes a number of dendrimers and the closely related star-like 120-123 polysiloxanes. Ihe hyperbranched polysiloxanes are the primary example of more random structures. Although the emphasis has been on synthesis and characterization,i i modeling on hyperbranched polymers has also been carried out. Some of the most interesting species involve polysiloxane chains. Star polymers, some with nanosized silica cores, have also been synthesized.i °-i i Hyperbranched polysiloxanes have been prepared with controllable molecular weights and polydispersities,i -1 - with epoxy terminal groups some are UV-curable ° and some serve as a source of molecular silica. Hyperbranched polysiloxanes have also been used in the sol-gel preparation of polypropylene/silica nanocomposites. ... 

Formation of claylike minerals is extremely slow if not impossible from sand, but will proceed under favorable conditions from colloidal or amorphous silica. Synthesis of montmorillonite in an autoclave at 300 C, is disclosed by Granquist (760). Hec-torite, a colloidal magnesium silicate in the form of molecularly thin ribbonlike crystals, was synthesized from silica gel (probably better from silica sol) by Granquist and Pollack (761). 

The sol-gel process has been used to produce various amorphous silica structures, such as tubular organogels by molecular imprinting. The use of supramole-cules for the synthesis of crystalline mesoporous materials via sol-gel processing is also well known. Preparation of a silica sol of controlled properties was demonstrated by Stober et al. in 1968 and is discussed here. 

The key effect of oxide supports on the catalytic activities of metal particles is exerted through the interface between oxides and metal particles. The key objective of this study is to develop synthesis methodologies for tailoring this interface. Here, an SSG approach was introduced to modify the surface of mesoporous silica materials with ultrathin films of titanium oxide so that the uniform deposition of gold precursors on ordered mesoporous silica materials by DP could be achieved without the constraint of the low lEP of silica. The surface sol-gel process was originally developed by Kunitake and coworkers.This novel technology enables molecular-scale control of film thickness over a large 2-D substrate area and can be viewed as a solution-based... 

Thus the sol-gel methodology is an alternative to classical thermodynamic routes for the synthesis of solids. It is also evident that the preparation of the solids through Chimie Douce bridges molecular chemistry and solid state chemistry. This chapter will be focused on material prepared by the sol-gel process, where an organic part is associated with a silica or siloxane Si—O—Si network. Two types of organic-inorganic hybrid materials can be prepared by the sol-gel process and are completely different the nanocomposites and the nanostructured hybrid materials6-9. 

For all these reasons, the guanine building blocks and the sol-gel chemistry were used as molecular precursor to conceive hybrid chiral materials at nanometric and micrometric scales. Our efforts involved the synthesis and the self-assembly of a guaninesiloxane monomer Gsi (Fig. 3) in the G-quartet and G-quadruplex supramolecular architectures (Fig. 6), which are fixed in a hybrid organic-inorganic material by using a sol-gel transcription process, followed by a second inorganic transcription in silica, by calcination. 

Nair BN, Yamagushi T, Okubo T, Suematsu H, Keizer K, and Nakao S-I. Sol-gel synthesis of molecular sieving silica membranes. J. Membr. Sci. 1997 135 237-243. 

Molecular composites in terms of synthesis The reinforcements are also formed by the in-situ reaction in the matrix polymers. Such methods are another way to pursue the limit of molecular dispersion of reinforcing materials. One example is found in the in-situ precipitation of reinforcing silica in polydimethyl siloxane networks with the sol-gel methods [21], Another example is the direct polycondensation of p-aminobenzoic acid or p-hydroxybenzoic acid from their monomers in solutions of polyarylate [22]. Mechanical properties of the cast films indicated increase in modulus and tensile strength at elevated temperatures. 

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