Octa -silsesquioxane

Within the now conventional group of liquid crystal dendrimers, a group of liquid-crystalline dendrimers based on the hexa- and octa-silsesquioxane... 

Fig. 31 The structures of the hexa- and octa-silsesquioxanes cores for use as scaffolds...

Star-like PFs 236 with a silsesquioxane core have been prepared by Ni-mediated copolymerization of 2,7-dibromo-9,9-dioctylfluorene with octa(2-(4-bromophenyl)ethyl)octasilses-quioxane [333]. The polymer is thermally stable up to 424°C (TGA). In both chloroform solution and films, its absorption and PL spectra are very close to that for PFO 196, although a somewhat higher PL efficiency is observed in films (64 and 55%, respectively). The polymer 236, however, demonstrates a better PL color stability during thermal annealing. An ITO/PEDOT/236/Ca/Ag device can be turned on at 6.0 V, and shows a brightness of 5430 cd/m2 (at 8.8 V) with F] =0.44%, almost twice as high as that for the corresponding PFO device (Chart 2.60). 

PDMS nanocomposites with layered mica-type silicates were also reported.374 A two-step sol-gel process of the in situ precipitation of silica led to the development of siloxane-based nanocomposites with particularly high transparencies.3 5 Some unusual nanocomposites prepared by threading polymer chains through zeolites, mesoporous silica, or silica nanotubes were reviewed.3 6 Poly(4-vinylpyridine) nanocross-linked by octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane was reported.377... 

The silylation of [(CH3) NOSiOj jjg by hexamethyldisiloxane in an aqueous propanol solution in the presence of hydrochloric acid affords octa(trimethylsiloxy-silsesquioxane) in good yield (75 %)... 

The reaction between the silsesquioxane HgSigOn and acetone in the presence of Co2(CO)8, and pyridine gives, after a six-week period for crystallization, a 35% yield of 27 (equation 9). This presumably occurs via initial formation of the octa-substituted (/-Pr( ))sSix( >i2 followed by partial hydrolysis of just two of the substituents to give the diol 27, which should be of use in the synthesis of polymeric silsesquioxanes119. 

Silsesquioxanes of Mixed Functionality -Octa[(3-chloropropyl)-/ipropyl-silsesquioxanes] and Octa[(3-mercaptopropyl)- propyl-silsesquioxanes] as Models of Organomodified Silica Surfaces... 

This compound and octa[mono(3-mercaptopropyl)-hepta( propyl)-silsesquioxane] [HS(CH2)3][H(CH2)3]7[SigO,2] 2.1 have been used as ligands in Rh(I) and Pt(II) transition metal complexes for modeling silica supported catalysts. 

In the work presented here organohmctional silsesquioxanes are used as models for organomodified silica surfaces. The main advantage is that organosilsesquioxanes are soluble in organic solvents in most cases making them susceptible to a wide array of analytical methods not available for amorphous materials. Of the many systems possible and worthy of attention, this study is limited to octa-(organosilsesquioxanes). 

Spherical siloxanes (RSiOi 5), with polyhedral frameworks, also called silsesquioxanes, can be used as defined oligomeric models for surface-modified silica gels or polysiloxanes. Whereas silsesquioxanes with alkyl-, aryl-, hydrido-, and trimethylsiloxy groups are known for a long time [1], functionalized octa-[propyl-silsesquioxanes], [X-(CH2)3]g(SiOi.5)g, were synthesized for the first time in 1990 by Weidner, Zeller, Deubzer, and Frey [2]. Octa[(3-chloropropyl)-silsesquioxane], [Cl-(CH2)3]g(SiO, 5)g, could be obtained by hydrolysis of (3-chloropropyl)-trichlorosilane. 

Recently Rinctionalized octa[(propyl)-silsesquioxanes] were obtained by hydrosilylation of Hg(SiO, 5)5 [3] with hinctionalized allylic compounds [4-8], In the following, the preparation of new functionalized propyl-silsesquioxanes by nucleophilic substitution or partial rearrangement of octa-[(3-chloropropyl)-silsesquioxane] is reported. 

Octa[(3-iodopropyl)-silsesquioxane] can be prepared by the Finkelstein-reaction treating octa-[(3-chloropropyl)-silsesquioxane] with sodium iodide in dry acetone under reflux. The structure of [I-(CH2)3]8(SiOi 5)g has been confirmed by X-ray crystallography [4, 5]. In the same way octa-[(3-thiocyanatopropyl)-silsesquioxane] was obtained. 

Octa [3-(diphenylphosphino)-propyl]-silsesquioxane was prepared by treating [Cl-(CH2)3]g(SiOi 5)g dissolved in THF with a solution of potassium diphenylphosphide in THF at room temperature ... 

The synthesis of octa [3-(methylmercapto)-propyl]-silsesquioxane was carried out by substitution of the chlorine atoms using sodium thiomethylate as nucleophilic agent. Because of the insolubility of NaSMe in toluene a phase transfer catalyst was used ... 

New Functionalized Silsesquioxanes from Octa[(3-chloropropyl)-silsesquioxane)] 693... 

Fig. 1. Octa-, deca-, and dodeca-silsesquioxane cage-types...

Fig. 2. NMR spectrum in CsDs of octa[(3-chloropropyl) silsesquioxane] (a), deca[(3-chloropropyI)-silsesquioxane] (b), and D2d-dodeca[(3-chloropropyl)-silsesquioxane] (c)...

The retention times are 8.2 min for [Cl-(CH2)3]g(SiOi 5)5, 16.0 min for [Cl-(CH2)3],o(SiOi 5)10 and 37.4 min for [Cl-(CH2)3]i2(SiOi 5)12 at 7 mL min flow rate. The substitution of the chlorine atoms at octa [(3-chloropropyl)-silsesquioxane] by acetoxy- or cyano groups is possible by using potassium acetate or sodium cyanide and 18-crown-6 as phase transfer catalyst in acetonitrile. In addition to the observed substitution, partial rearrangement to the greater deca- and dodeca-silsesquioxane cages, also took place. 

Tanaka et al. [101] synthesized octa(aminophenyl)silsesquioxane (GAPS), an aromatic amine-functionalized silsesquioxane free from aliphatic components. GAPS reacts rapidly with the 2-pyridinecarboxaldehyde under mild conditions, giving an imine that emits green fight under UV illumination. 

The aniline groups of octa(aminophenyl)silsesquioxane (OAPS) offer versatility both as reaction sites to which other nanobuilding blocks can be... 

Liquid-crystalline (LC) silsesquioxanes having various mesogenic moieties were synthesized by the hydrosilylation reaction of octa(hydridosilsesquioxane) and terminal alkenes with mesogenic groups using hexachloroplatinic acid as a catalyst... 

Synthesis of Homo- and Mixed-Functionalized Octa-, Deca- and Dodeca-Silsesquioxanes by Cage Rearrangement and their Characterization... 

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