Silsesquioxanes cations

These spacings correspond to cationized fragments with the general composition [SixOyHz]+. The results of the peak analysis prove that the uppermost monolayer of the surface film consists of totally hydrolyzed polymeric siloxanes. There is evidence that these fragments appear as ring- and cage-like silsesquioxane cations (Fig. 2) ... 

Crivello, J. V. Malik, R. Synthesis and Photoinitiated Cationic Polymerization of Monomers Containing the Silsesquioxane Core. In Silicones and Silicone-Modified Materials-, Glarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Eds. AGS Symposium Series 729 American Chemical Society Washington, DC, 2000 pp 284-295. 

Figure 5.4 Reaction of the silsesquioxane-borato complex PhN(H)Me2 [(c-C5H,),SUO,3]B(QF5)3 (5) with [Cp2Zr(CH2Ph)2] to afford well-defined cationic species 7-9. (Redrawn from Duchateau et al. [15].)...

Scheme 14.5 Cationic Zr(iV) surface species obtained from Cp ZrMe3 with silica, and possible silsesquioxane models.

In summary, zirconocene and half-sandwich zirconium-based catalysis has been developed both in surface and solution systems. In general, the activation of Zr-POSS and silica-supported zirconium system with MAO proved inappropriate (see silsesquioxane displacement and leaching, respectively, vide supra), while the acti-vahon with BArl proved more efficient, albeit structural rearrangement complicates the activation chemistry and simple Zr(IV) cationic alkyl species are seldom the outcome of the activation. 

To test the ability of the silsesquioxanes to function as ligands to alkali cations, a lO" m aqueous solution of picric acid with 2x10 mol alkali hydroxide was mixed with a 10 m solution of the silsesquioxane in CH2CI2 according to [7]. The concentration of the picric acid anions was determined by measuring the extinction of the absorption band at 370 nm and using the Beer-Lambert law... 

Crivello, J.V. Malik, R. Synthesis and photoini-tiated cationic polymerization of monomers with the silsesquioxane core. J. Polym. Sci. Polym. Chem. 1997, 35, 407. 

Cations based on substituted silsesquioxanes have also been intercalated [7]. On heating the ion-exchanged clay minerals water is evolved, but oxycation or oxide pillars keep the siliceous layers apart. These materials have enhanced thermal stability compared with clay minerals expanded with organic cations. Expanded clay minerals cover at least as wide a range of accessibilities to the interlamellar micropore spaces as the zeolites, but the pore characteristics of clay minerals with inorganic pillars need more detailed investigation. 

The PDMAEMA stars are weak cationic polyelectrolytes. But they can be easily transformed into strong cationic polyelectrolytes poly [2-(methacryloyloxy)ethyl] trimethylammonium iodide] (PMETAI) stars by quaternization with methyl iodide. Asymmetric field flow fractionation (AFFF) measurements showed that the silsesquioxane core remained intact. The PMETAI brushes were also subjected to... 

It is possible to observe the morphologies of the cationic PMETAI stars in solution by cryogenic transmission electron microscopy (cryo-TEM). Figure 1 clearly shows the distinct and well-separated structures in the vitrified solution. In some cases it is even possible to see the silsesquioxane core [28],... 

Mesoporous organosilicates are synthesized using similar self-assembly approaches as pure silica meso-phases the main difference being the silicon-containing precursors that consist of bridged silsesquioxanes, (RO)3Si-R -Si(OR)3. Different types of amphiphile molecules, including cationic (alkyltrimethylammonium),... 

Synthesis and Photoinitiated Cationic Polymerization of Monomers Containing the Silsesquioxane Core... 

A synthetic scheme was developed to prepare cationically polymerizable octafunctional monomers with cubic silsesquioxane (Tg) cores. Epoxy and 1-propenoxy functional groups were attached... 

The present work focuses on the synthesis of novel multifunctional epoxy and vinyl ether monomers bearing the Tg silsesquioxane core and a study of their behaviour under photoinitiated cationic polymerization conditions. 

A series of octafunctional epoxy and 1-propenyl ether monomers bearing the Tg silsesquioxane core have been prepared and characterized. Despite the high functionality and reactivity of these monomers, the efficiency with which the monomers undergo crosslinking is considerably less than expected. Instead, due to steric inhibition effects and the proximity of the functional groups to one another, photoinduced cationic polymerization proceeds mainly by an intramolecular process. 

Fox DM, Maupin PH, Harris RH, Gilman JW, Eldred DV, Katsoulis D, et al. Use of a polyhedral oligomeric silsesquioxane (POSS)-imidazolium cation as an organic modifier for montmorillonite. Langmuir 2007 23 7707-14. 

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