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.

Polyhedral oligomeric silsesquioxanes (POSS) have been explored for over 7 decades. These organic/inorganic nanostructures are extremely versatile compounds that are compartible with polymer systems, hence making them ideal components for the synthesis of next generation hybrid materials. Their properties may vary based on the organic peripheral unit, but they are generally environmentally friendly, cheap, easy to process, highly soluble in organic solvents, and exhibit high thermal degradation temperatures, low dielectric constant and high degree of hardness as coating agents. These features of silsesquioxanes have led to a growing interest in the exploration of their chemistry, particularly on their synthesis and applications in polymer synthesis, catalysis, biomedical materials, and electronics. Cubic silsesquioxanes and their double decker (DDSQ) counterparts have been the most useful because these compounds possess the architecture that accommodates functionalization. However, most of the progress recorded to date has been limited to either manipulations on the closed cubic structures or use of double deckers to synthesize functionally symmetric POSS compound. These compounds do display the desired physicochemical properties, but their applications pose the challenge of tethering them with two dissimilar polymeric chains.In this thesis, efforts have been made to develop a route for the selective synthesis of asymmetric POSS compounds that are likely to provide more resourceful applications to the polymer and material sciences. The research utilized the versatility of protecting groups to effect selective functionalization of the DDSQ for entry into the desired target. The asymmetric POSS cage has the potential to allow its dispersal into two dissimilar polymer matrices, generating a POSS/polymer composite that is unprecedented.

The commercial availability and decreasing cost of polyhedral oligomeric silsesquioxanes in recent years has opened up the field to everybody who wishes to apply these unique properties in their own technologies. This is the first book to provide a comprehensive overview of these applications, and covers the synthesis, characterization and history of polyhedral oligomeric silsesquioxanes, their use as metallasilsesquioxane catalysts, their effect upon polymer properties and plastics performance, and their use in superhydrophobic nanocomposites, and electronics, energy, space and biomedical applications. "Applications of Polyhedral Oligomeric Silsesquioxanes" is a valuable reference for those working across a range of disciplines, including chemists, materials scientists, polymer physicists, plastics engineers, surface scientists, and anybody with a commercial or academic interest in plastics, composite materials, space materials, dental materials, tissue engineering, drug delivery, lithography, fuel cells, batteries, lubricants, or liquid crystal, LED, sensor, photovoltaic or biomedical devices.

This book provides an overview of polymer nanocomposites and hybrid materials with polyhedral oligomeric silsesquioxanes (POSS). Among inorganic nanoparticles, functionalized POSS are unique nano-building blocks that can be used to create a wide variety of hybrid and composite materials, where precise control of nanostructures and properties is required. This book describes the influence of incorporation of POSS moieties into (organic) polymer matrices on the mechanical, thermal and flammability behavior of composites and hybrid organic-inorganic materials. Importantly, POSS-containing materials can be bio-functionalized by linking e.g. peptides and growth factors through appropriate surface modification in order to enhance the haemo-compatibility of cardiovascular devices made of these materials. This volume includes descriptions of synthesis routes of POSS and POSS-containing polymeric materials (e.g. based on polyolefines, epoxy resins and polyurethanes), presentation of POSS’ role as flame retardants and as biocompatible linker, as well as the depiction of decomposition and ageing processes.

With the recent advent of nanotechnology, research and development in the area of nanostructured materials has gained unprecedented prominence. Novel materials with potentially exciting new applications are being discovered at a much higher rate than ever before. Innovative tools to fabricate, manipulate, characterize and evaluate such materials are being developed and expanded. To keep pace with this extremely rapid growth, it is necessary to take a breath from time to time, to critically assess the current knowledge and provide thoughts for future developments. This book represents one of these moments, as a number of prominent scientists in nanostructured materials join forces to provide insightful reviews of their areas of expertise, thus offering an overall picture of the state-- the art of the field. Nanostructured materials designate an increasing number of materials with designed shapes, surfaces, structures, pore systems, etc. Nanostructured materials with modified surfaces include those whose surfaces have been altered via such techniques as grafting and tethering of organic or organometallic species, or through various deposition procedures including electro, electroless and vapor deposition, or simple adsorption. These materials find important applications in catalysis, separation and environmental remediation. Materials with patterned surfaces, which are essential for the optoelectronics industry, constitute another important class of surface-modified nanostructured materials. Other materials are considered nanostructured because of their composition and internal organization.