Study of different routes to develop asymmetric double decker silsesquioxane (DDSQ)

Silsesquioxane cages can be considered as well-defined nanosized molecules (1-3 nm) and have attracted widening interests due to their possible use as components of resourceful inorganic/organic hybrid materials, as well as their applications in optics, catalysis, polymers and electronics. Double-decker silsesquioxane (DDSQ) nanoparticles have attracted much attention recently due to the ease of which these particles can be incorporated into polymeric materials and their unique capability to reinforce polymers.These systems are of high interest to scientists, due to their unique chemical and physical properties (solubility, non-flammability, oxidation resistance, and very good dielectric properties). For example, the United States Air Force and NASA use DDSQ incorporated polymers as thermoset material and flame retardants.;This thesis discussed mainly three projects. One project centered on the research to improve and optimize the synthetic routes for a large scale synthesis of DDSQ functionalized oligoimides. These procedures offer the opportunity to combine several synthetic steps into a single reaction vessel, thereby cutting processing time and costs. The second project discussed is on the synthesis of a novel (phenylethynyl)phenyl DDSQ oligomer that can be used for high temperature application. This oligomer was successfully synthesized through a one pot route with 70% yield by avoiding the tedious separation techniques, fractional distillations and Kugelroher distillation. This novel oligomer will be characterized using TGA (Thermal Gravimetric Analysis) and DSC (Differential Scanning Calorimetry) for future studies. Another novel synthetic approach towards the synthesis of (phenylethynyl)phenyl DDSQ oligomers is also discussed. This new approach was based on Pd-catalyzed silylation of aryl halides. Even though Pd-catalyzed silylation of aryl halides was successful for the T7(iBu) cage, this chemistry was not applicable for DDSQ-H cage. The main project was on studies of different routes to an asymmetric DDSQ cage. DDSQ molecules possess a higher symmetry. Breaking the symmetry and selective functionalization of the DDSQ molecule would be highly desirable to fine tune the physical properties. Different routes were studied to develop an asymmetric DDSQ cage. One route is monoprotection of a hydroxyl group from four symmetrical hydroxyl groups present in the DDSQ cage using McDougal chemistry. This chemistry was applied to DDSQ cage, DDSQ(Me)(OH) and DDSQ(Me)(Hydroxypropyl)(carbinol system). The second attempt was hindering one side of the DDSQ cage using an immobilized surface. Different surface immobilized reagents such as "Red-Sil" (Reducing Silica) and Merrifield resinwere analyzed in this project as screening surfaces.