Non-hydrolytic sol-gel process

PMMA-Si02-Zr02 nanohybrid films were prepared successfully using a novel non-hydrolytic sol-gel process and, owing to their excellent optical transparency combined with high thermal stability, were stated to have high potential in applications for optical devices at elevated temperatures [307]. 

Acosta S., Corriu R.J.P., Leclercq D., Lefevre P., Mutin P.H., Vioux A. Preparation of alumina gels by a non-hydrolytic sol gel processing method. J. Non-Cryst. Solids 1994 170 234-242 Acosta S., Corriu R., Leclercq D., Mutin P.H., Vioux A. Novel non-hydrolytic sol-gel route to metal oxides. J. Sol-Gel Sci. Tech. 1994 2 25-28... 

Crouzet L., Leclercq D. Polyphosphazene-metal oxide hybrids by non-hydrolytic sol-gel processes. J. Mater. Chem. 2000 10 1195-1201... 

Hay J.N., Porter D., Raval H.M. A versatile route to organically-modified silicas and porous sihcas via the non-hydrolytic sol-gel process. J. Mater. Chem. 2000 10 1811-1818 Hay J.N., Raval H.M. Synthesis of organic-inorganic hybrids via the non-hydrolytic sol-gel process. Chem. Mater. 2001 13 3396-3403... 

Janackovic D., Orlovic A., Skala D., Drmanic S., Kostic-Gvozdenovic L.K., Jokanovic V., Uskokovic D. Synthesis of nanostructured mullite from xerogel and aerogel obtained by the non-hydrolytic sol-gel method. Nanostructured Mater. 1999 12 147-150 Jansen M., Guenther E. Oxide gels and ceramics prepared by a non-hydrolytic sol-gel process. Chem. Mater. 1995 7 2110-2114... 

Both stages are controlled by condensation chemistry that can include, as a first step, hydrolysis of hydrated metal ions or metal alkoxide molecules [6, 7] (hydrolytic sol-gel processing). The condensation chemistry in this case is based on olation/oxolation reactions between hydroxylated species. The hydroxylated species for further condensation can be formed also by a non-hydrolytic route, that is, by reactions between metal chlorides and alcohols with electron-donor substituents [8]. The nonhydrolytic sol-gel processing may... 

Commonly two main sol-gel methods are used. The first one involves aqueous solutions of salt precursors in which the formation of hydroxyl species, then their polycondensation, is induced by varying the pH. The second method consists of generating the hydroxyl species by hydrolyzing metal-organic molecular precursors, such as alkoxide derivatives, most often in alcohohc solution. Therefore the terms sol-gel and water are closely related, and the term non-hydrolytic sol-gel sounds incongruous. However, the desire to explore new condensation reactions in low-temperature processes where kinetics control the structure and the texture of the products has prompted some interest in non-hydrolytic sol-gel methods over the last decade. Some conprehensive reviews have been pubhshed on the topic (Vioux, 1996, 1997 Hay, 2001). This chapter aims at outlining the main results reported in the area, including in the most recent period. 

Sol-gel processing can be roughly divided into two areas based on the type of precursor used the alkoxide route, i.e., the controlled hydrolysis and condensation of a hydrolytically unstable precursor (usually based upon a metal alkoxide species) soluble in non-aqueous solvents and the colloidal route, the peptidization of a water-soluble precursor (also known as colloidal processing). Hydrolysis of an aqueous metal precursor occurs on changing the pH of the precursor solution. These types are usually discussed separately. 

The sol-gel methodology can also be applied to non-hydrolytic processes. The preparation of methylsilsesqui-oxane-titanium oxide hybrid by the etherolysis-condensation of a mixture of methyltrichlorosilane and metal chloride,353 354 and by the condensation of preformed poly(methylsilsesquioxane) carrying Si-OH and Si-OCHj groups with titanium(iv) -butoxide,355 has been reported. 

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