Silsesquioxane

These adsorbents have cross-linked silsesquioxane stmcture. They are stable up to 230-270°C and do not lose their sorption activity in 10-18 M H3SO4 at 100°C in boiling concentrated hydrochloric acid. 

Supramolecules and supramolecular assemblies including silsesquioxanes and azacrown ethers fragments as liquid crystals with restricted molecular topology 98CC2057. 

The Si NMR chemical shifts for several Tg derivatives are shown in Table 2. The alkyl derivatives fall in the range —54 to —57ppm, while the aryl derivatives are more upheld from —66.9 to —68.9 ppm, as expected for aryl versus alkyl substituents. Bassindale et al. have derived a relationship, = 0.82 x Tg/ allowing an estimation of the chemical shift for unknown Tg derivatives from the known values for the much more common Tg analogs. The solid-state Si NMR spectrum for Tg[OSiMe3]g shows five signals for the silsesquioxane silicon atoms. 

The reactions of POSS molecules fall into two categories, those involving the silsesquioxane core of the molecule and those involving reactions of the peripheral substituents. The silsesquioxane core in POSS compounds is fairly unreactive to many reaction conditions and this inertness has led to the successful application of POSS species in many materials (see Section V for further... 

Figure 11 Base-catalyzed cage rearrangement of alkyl silsesquioxanes.

Polyhedral oligomeric silsesquioxane (POSS)-based nanocomposites... 

Nanocomposite based on polyurethane (PU) is prepared using silica, clay, and Polyhedral Oligomeric Silsesquioxane (POSS). Preparation, characterization, mechanical and barrier properties, morphology, and effect of processing conditions have been reported on polyurethane-based nanocomposites [72,73]. 

Polyhedral oligomeric silsesquioxane (POSS) has been extensively studied as starting substrate to construct nanocomposites with precise control of nanoarchitecture and properties. Octahedral derivatives are the most representative ones of this family. It was reported that the HRP-catalyzed conjugation of catechin on amine-substituted octahedral silsesquioxane amplified the beneficial physiological property of flavonoids. The POSS-catechin conjugate exhibited great... 

The use of small polyhedral silsesquioxanes as molecular models of silica surfaces has been studied increasingly in recent years, because catalysts, etc., attached to such species are relatively easy to handle and characterize when compared to bulk silica. The preparation and structures of silsesquioxanes used in this type of work are described later in Sections II,C, IV,E, and IV,F. Further recent examples may be found in Ref. 5. 

Silylation of the silsesquioxane [(C6H11)7Si709(0H)3] (see Section IV,E for its structure) leads to disilanols [(C6Hn)7Si709(0H)2SiMe2R] (R = Me or Ph). The structure of the phenyl compound 59 shows the... 

Evaluation of the peak pattern gives evidence of silsesquioxanes and their homo-derivatives as well as high molecular reaction products with ladder-like structures. The presence of cage-like polysiloxanes is remarkable since their formation generally requires completely different preparative conditions [10],... 

Figure 4. Peak assignment of spherical silsesquioxanes and homo-silsesquioxanes obtained from CH3SiX3 the accurate masses were determined by means of high resolution TOF-SIMS (the O-atoms located on the edges of the polyhedra are not shown).

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) ... 

Fig. 10.7 Crystal structure of com pounds 4 stick representation of H-bond (dotted lines) superstructures of (A) phenyl, (B) indole, (C) phenol ureido-silsesquioxanes H atoms were omitted for clarity.

---