POSS cages

POSS cage Si only, referenced to SiMe4. For an alternative s)mthesis see Section V.E. 

However, other data such as the small difference observed in the Si NMR chemical shift (0.9 ppm upheld from TgPhg) and the absence of any measurable Si-F coupling show that the interaction between the huoride ion and the silicon atoms is small. Studies to evaluate the collision cross section of TgPhg using Na show that the cation attaches itself to the outside of the POSS cage and does not significantly distort the structure. 

Examples of the synthesis of polysiloxane nanocomposites reported in the literature include Work by Ma et al (6) who modified montmorilIonite with short segments of PDMS and blended this into a polymer melt/solution to yield examples of fully exfoliated or intercalated PDMS/clay nanocomposites. Pan, Mark et al (7) synthesized well defined nano-fillers by reacting groups of four vinyl terminated POSS cages with a central siloxane core. These materials were subsequently chemically bonded into a PDMS network yielding a significant improvement in the mechanical properties of the polymer. 

These interesting POSS features, briefly mentioned above, have motivated this work to critically review recent developments in the syntheses of POSS polymer materials to form POSS nanocomposites. The work further examines the properties of POSS nanobuilding blocks that can otherwise be used for developing polymeric nanocomposites. In particular, the syntheses of POSS cages, monomers containing POSS cages, POSS-dendrimers cores, POSS-containing polymers and POSS nanocomposites are covered in details. It should be emphasized that the assessment of the relationship between the... 

Fig.1 Four typical structures of POSS cages a trigonal prismatic (SigOg) cage, b cubane (SisOn) cage, c double five-ring (SiioOis) cage, and d double six-ring (SinOis) cages...

It is evident that the incorporation of POSS cages into polymeric materials often results in substantial improvements in polymer properties and offer the possibility to control the mechanical, chemical and physical properties of the system during polymerization as well. Intense efforts have recently been directed toward the development of new porous materials because of their utihty and potential utihty as catalysts and catalyst supports [208,209], dielectric materials for electronic appHcations [210], media for optical [211] and sensor [212] applications, and selectively permeabihty membranes [213] and precursors [10] for POSS nanocomposites. Significant property enhancements imparted by the inclusion of a nanosized inorganic... 

These cages could easily be separated by selective crystallization. Such a rearrangement and scrambling of POSS cage structures is commonly... 

Scheme 4.14. Synthesis of 4-TMSPh-POSS cages in the presence of TBAF.

Since a POSS molecule has both defined structure and specific functional groups, it provides the possibility of preparing nanocomposites with controlled structures. There has been considerable effort using POSS cages as building blocks to make controlled structure materials. 

Franchini et al. [96] used monofunctional POSS (4 or 9 wt%), containing isobutyl or phenyl bonds, into an epoxy-amine and fire retardant properties were evaluated. The fire behavior is clearly modified by the presence of the POSS clusters for both types of POSS cages, a significant decrease is observed in the PHRR. In the case of... 

Another important area of research in biocompatible SMPINCs is the use of polyhedral oligomeric silsesquioxanes (POSS). In recent studies, these POSS cages primarily served as anchor sites for PCL chains to make organosilica SMPINCs with a wide variety of properties, ranging from triple-shape POSS/PCL networks [116], dynamic microscale surface features [117], ultrasoft networks post-transition... 

The order of permeability coefficient for the four gases through these PI-POSS hybrid membranes was P (CO2) > P (O2) > P (N2) > P (CH4), which follows the same order as their kinetic diameter (A) CO2, 3.3 O2, 3.46 N2, 3.64 CH4, 3.8 [109]. Compared with the pure PI membranes, a significant increase in permeability coefficient values was observed for all of the PI-POSS hybrid membranes, whereas the selectivity was comparable for different gas pairs. The higher permeability coefficients for the hybrid membranes were attributed to the presence of bulky porous POSS cages... 

Interesting PEO-containing block copolymers were synthesized by Lee et al. [68]. These authors attached oligomeric silsesquioxane (POSS) cages to the termini of a middle PEO block to produce BAB-type block copolymers. The resulting polymers form stable monolayers, the properties of which depend on the block... 

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