Trialkoxy alkyl silanes

Trialkoxy alkyl silanes are effective dispersants for silica because they can bond to the surface silanols. However, that type of dispersant has inappropriate chemistry to bond to calcium carbonate and is therefore ineffective on that type of filler (Fig. 22.3). 

Shimojima, A., Sugahara, Y., and Kiuoda, K. (1997) Inorganic-organic layered materials derived via the hydrolysis and polycondensation of trialkoxy(alkyl)silanes. Bull. Chem, Soc. Jpn., 70, 2847-2853. 

Apart from the reaction with halogen derivatives, use was also made, for the synthesis of silicon-containing cellulose esters, of the reaction of alcoholysis, with cellulose, of tetraalkoxysilanes or alkyl(aryl)trialkoxy-silanes and the amides of siliconic acids (64) ... 

From the above discussion, it becomes obvious that what is needed to impart mobility to backbone-atoms during the gelling of the polymer is to block one substituent of the silicon. Blocking by a less-reactive bulky alkoxy-substituent is undesired since it implies a penalty of an increased contraction due to the increased volume, and yet cracking can start eventually when this group will be hydrolyzed.The better alternative is to select a monomer with a single blocked substituent, which is non-reactive under the mild conditions of the sol-gel reaction. Such monomers are the alkyl-trialkoxy-silanes R -Si(OR)3. This type of monomer is analogous to Al(OR)3, monomers for which successful formation of thin-films by the sol-gel technique has been recently reported (16-18). 

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