ORganically Modified SILicas ORMOSILs

On the basis of the sol-gel process, much more attention has been paid to silicate-containing Class II hybrids, also referred to as organically modified silicas, ormosils. In this section, the synthesis of some of the most characteristic ormosils for bone and dental applications are described. 

Fig. 1 Chemical structures of the polymers commonly used for preparation of beads poly (styrene-co-maleic acid) (=PS-MA) poly(methyl methacrylate-co-methacrylic acid) (=PMMA-MA) poly(acrylonitrile-co-acrylic acid) (=PAN-AA) polyvinylchloride (=PVC) polysulfone (=PSulf) ethylcellulose (=EC) cellulose acetate (=CAc) polyacrylamide (=PAAm) poly(sty-rene-Wocfc-vinylpyrrolidone) (=PS-PVP) and Organically modified silica (=Ormosil). PS-MA is commercially available as an anhydride and negative charges on the bead surface are generated during preparation of the beads...

Related and Modified Reagents. In addition to the standard reagent, a polymer-supported perruthenate (PSP) compound has been described. i Recent work has also examined the doping of organically modified silicas (ormosils) with TPAP via a sol-gel process, 7 which enhances the general versatility and reusability of TPAP catalysts. The use of supercritical carbon dioxide as a solvent has also been investigated. TPAP has also found use as a convenient source of ruthenium in mthenium-catalyzed hypochlorite oxidations. ... 

It is interesting to analyze the effect of inorganic fillers or blending with other polymers on the methanol uptake of Nafion-based membranes. Kim et al. [46] measured methanol uptake in composite of Nafion with organic modified silica (ORMOSIL) and they observed that the methanol uptake decrease proportionally to the amount of inorganic phase in the membrane, reaching a half of its value in Nafion when the filler content is close to 40 wt%. The connectivity between the... 

Furthermore, the same sol-gel matrices have been used in a system where acid and base catalysis occur in the same pot without quenching either catalyst [29]. In this case, the acids were either entrapped Nafion (perfluorinated resin sulfonic super acid, a3) or entrapped molybdic acid (M03-Si02, a2), while the bases were two ORMOSILs (organically modified silica sol-gel materials), one with H2N (CH2)2NH(CH2)3 groups (bi) and the other guanidine base residues (b2) (Scheme 5.12). 

An example of the appropriate application of organically-modified silica precursors is alkoxides with an alkyl group. When methyltrimethoxy- or methyl-triethoxysilane (Figure 3.2) was added in formulations to increase the hydro-phobicity of ORMOSILs, it resulted in a better enzymatic activity of lipases immobilized in the alkyl-modified silica than in a hydrophilic matrix fabricated by means ofTEOS alone [51,80,129-133]. Similarly, an increased stability of lipase from Candida antarctica B was observed after its immobilization in a silica matrix... 

Finally, some hybrid inorganic-organic materials such as Ormosil (=Organically modified silica) are also very popular. The structure and properties of Ormosils resemble those of silica and organic polymers. 

PEBBLEs are water-soluble nanoparticles based on biologically inert matrices of cross-linked polymers, typically poly(acrylamide), poly(decylmethacrylate), silica, or organically modified silicates (ORMOSILs), which encapsulate a fluorescent chemo-sensor and, often, a reference dye. These matrices have been used to make sensors for pH, metal ions, as well as for some nonionic species. The small size of the PEBBLE sensors (from 20 to 600 nm) enables their noninvasive insertion into a living cell, minimizing physical interference. The semipermeable and transparent nature of the matrix allows the analyte to interact with the indicator dye that reports the interaction via a change in the emitted fluorescence. Moreover, when compared to naked chemosensors, nanoparticles can protect the indicator from chemical interferences and minimize its toxicity. Another important feature of PEBBLEs, particularly valuable in intracellular sensing applications, is that the polymer matrix creates a separate... 

In this chapter, recent progress in several key areas is reviewed. These areas are catagorized by material classification rather than by end-use application (1) bulk silica optics (2) optically active doped silica glasses (3) gel-polymer composites (4) organically modified silicates (ormosils) and (5) gradient-index glasses. These represent the five most significant developments in the area of bulk optical materials by the sol-gel process to date. 

Within the examples appearing in the hterature, the synthetic strategy used by Prasad and coworkers to obtain the so-called ORMOSIL (ORganic-Modified SILica) nanoparticles stands out for versatility and simplicity. It is based on an... 

Figure 25-2. Microstructure of an organically modified silicate (Ormosil). Poly (dimethyl siloxane) chains combine silica blocks derived from hydrolysis of an alkoxysilane, Si(OR)4.

In recent years, silica sol-gel-based inorganic-organic hybrid materials have also been reported. The introduction of various functional groups into organic alkoxide has led to organically modified sol-gel glasses (ormosils). Some of the ormosil monomers and ormosil formations can be found in Fig. 16.3. Redox molecules can be coupled with the ormosil monomer functional group. The immobilized redox molecules can... 

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