Organically-modified Precursors

Organically-modified silica precursors have three alkoxy groups. As a result, alcohol is separated after the hydrolysis. Its appearance causes a detrimental effect on biopolymers typical to that ofalkoxides. The next disadvantage of these precursors is the absence of universality. They are appropriate only in particular cases. 

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Ormosils are prepared in a manner very similar to conventional sol-gel solutions, except that in addition to the conventional alkoxide precursor, another organically modified precursor is added [50], For example, ormosils have been... 

Simon P.F.W., Ulrich R., Spiess H.W., and Wiesner U. Block copolymer-ceramic hybrid materials from organically modified ceramic precursors, Chem. Mater., 13, 3464, 2001. 

Precursors are generally ORMOSILs, that is, organically modified silicates. The procedure for metal catalysts is similar to that for lipases, apart from the use of an argon atmosphere. More details of these procedures can be found in the literature [26]. 

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... 

Another unique aspect of the sol-gel process in this context is the synthesis of Ormo-cers (organically modified ceramics)111. Different organic-inorganic sol-gel precursors have been used for this purpose for the development of new glasses with second-order nonlinearities257-261. In these materials, organic chromophores are chemically bonded... 

The ultimate objective of this investigation is the synthesis of advanced and thermally stable organically modified siloxanes by incorporation of 6-membered ring structures of triamino triazine A and cyclophosphazene B (Fig. 1.). It is therefore necessary to synthesize novel monomeric precursor compounds for sol-gel processing, which possess 6-membered ring structures chemically linked to alkoxysilyl moieties. 

Sol-gel techniques were used to prepare porous, organically modified silica materials. The introduction of organic groupings was carried out with alkoxysilanes as precursors methyl and propyl amino groups were used. The results show that high-porosity materials can be synthesized the microstructure strongly depends on reaction conditions such as composition, solvent, catalyst type, and concentration. Microstructure tailoring affects mechanical as well as adsorption properties, and custom-made materials such as abrasives and adsorbents with special properties were synthesized. 

In some cases the heterogeneous version of a catalyst can be prepared by direct reaction of that catalyst with a suitable support material. Thus reactive Lewis acids such as aluminium chloride will react with hydroxylated materials such as silica gel to give directly bonded surface species such as -OAICI2.20 Another single-step route to the supported catalyst is via sol-gel techniques, typically to produce an organically modified mesoporous silica. This is based on the co-polymerisation of a silica precursor and an organosilicate precursor (Figure 1.5). 

Recently, Reetz and others have published a number of studies showing that adding organically modified silanes (precursors), such as methyltrimethoxysilane or poly (dimethylsiloxane), to tetraethoxysilane (TEOS) during hydrolysis can produce a protein-doped organicinorganic hybrid material that is hydrophobic [1-7]. Systems already tested... 

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