Sol-gel condensation

Since sol-gel polycondensation and organic polymerization usually take place under different reaction conditions, the sequence of the reactions (organic polymerization prior to sol-gel condensation or vice versa) can be chosen by reaction conditions. 

Since sol-gel condensation and ring opening reaction take place under... 

Figure 8.25 Sol-gel condensation of PhSi(OMe)3 (35) within case 2 to give cyclic trimer 36.

Depending on the size of the ligand, the inner cavity of these structures had a diameter of 2-4 nm, along with 96 inward-facing hydroxyl groups. Addition of tetramethoxysilane resulted in sol-gel condensation exclusively inside the host, thus producing silica nanoparticles of defined size and shape—the size and shape of the host s inner cavity. Despite the amorphous nature of silica nanoparticles, the polydispersities observed approached unity. No side reactions, such as condensation outside the spheres or... 

Figure 11 Sol-gel condensation of tetramethoxysilane inside a self-assembled organopaUadium sphrae produces monodisperse silica nanoparticles. (Reproduced with permission from Ref. 44. Nature Publishing Group, 2010.)...

Sol-gel condensation polymerizations have also been carried out using either photogenerated acids or bases as catalysts. For example, Hanson and Jensen employed a (diphenylmethyl)trimethylammonium salt as a photolatent source of trimethylamine to conduct the sol-gel condensation of tetraethoxysilane (Scheme 7). Postirradiation heating at 65 °C was necessary to drive the reaction to completion. Crivello and Mao and Croutxe-Baghorn have reported similar sol-gel condensation polymerizations of alkoxysi-lanes conducted using diaryliodonium salts as photoacid generators. 

Scheme 7 Sol-gel condensation polymerization of tetraethoxysilane conducted using a photolatent base.

Fattier, B., Henderson, M., Brotons, G., and Gibaud, A. (2010) Study of titanium oxide sol gel condensation using small angle X-ray scattering. / Phys. Chem. B,... 

Sol-gel condensation of encapsulated tetrame-thoxysilane guest molecules within the spherical cavities of coordination capsules 529 and 530 has been used in [4] for preparation of monodisperse silica nanoparticles by Scheme 5.4. 

Sol-gel chemistry and processing was a facile and efficient methodology for the preparation of branched, star-shaped homopolymers. The hydrolysis and condensation reactions are efficiently catalyzed with either simple acids or bases, and it was possible to control the nature of the silicate-like hub by judicious selection of the catalyst. The sol/gel condensation reactions to form the branched pol)miers occurred readily in the solid state above the glass transition temperature. The sol-gel process generates a silicate-like hub that contains... 

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