This dissertation is an account of my efforts toward developing strategies for the synthesis of novel functionalized polyhedral oligomeric silsesquioxanes (POSS). These organic/inorganic nanomaterials date back to 1946 and the pioneering work of Scott's synthesis of octamethylsilsesquioxane. POSS cages constitute a framework of silicon-oxygen polyhedron with reactive or inert organic coronae. These hybrid nanostructures are versatile precursors that find applications in polymer chemistry, catalysis, engineering, medicine, and electronics. Their properties are partly dictated by the peripheral organic groups. They are generally benign and easily processible into composite materials with high thermal degradation temperatures, low dielectric constants and superior mechanical properties. These features of POSS compounds have prompted growing interest in their exploration, particularly their use as models for the synthesis of the next generation hybrid nanocomposites. POSS molecules come in different cage sizes with condensed and incompletely condensed structures. The completely condensed analogues are denoted as Tn, where n = number of silicon atoms in the cage and n ⁹́Æ 6. Whereas the cubic/condensed silsesquioxanes were the initially discovered compounds, most explorations today are focused on the incompletely condensed di-, tri-, and tetra-functional scaffolds because of the ability to derivatize them into more functional materials for a myriad of applications. Even with the partially condensed structures, current research focus on this family of compounds has been dominated by the highly symmetric tetrafunctional octasilsesquioxane otherwise known as the double-decker oligomeric silsesquioxane. This functional POSS precursor has enormous potential for the synthesis of nanosized hybrid clusters with defined shape, structure, and physicochemical properties.In this study, efforts have been made to disclose strategies for the synthesis of asymmetrically functionalized double-decker shaped silsesquioxanes that can serve as nano-linkers to two dissimilar polymer matrices. The conversion of dead-end silsesquioxanes into more functional cage precursors, and surface transformation of cubic and functionalized DDSQs into modifiable precursors for the synthesis of well-defined 3D networks well among my aims. POSS cages used in these investigations were obtained either from commercially available cages or cage-like precursors or were synthesized from monomeric trialkoxy- (or trichloro-)silanes by hydrolytic condensation. Products obtained from this study could open an avenue for the exploration of new structure/property relationships and provide a unique way by which cages can be used as linkers to form both linear POSS/polymer and 3D networks. This research promises to open a new research direction for the synthesis of novel materials that combine three unconventional materials into hybrid POSS/polymer composites. With the asymmetric POSS cage as the building block, unprecedented properties may emerge from the synergy of these building blocks.
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