Synthesis and characterization of organically-bridged polysilsesquioxanes: New hybrid organic-inorganic synthetic glasses

This dissertation focuses on the development of new hybrid organic-inorganic materials. These materials have the potential to combine the properties of inorganic oxides (thermal stability, hardness) and organic polymers (ease of processing, high tensile strength, functionality). An approach to the syntheses of these unique hybrid materials has been developed in our lab. This strategy involves sol-gel chemistry of organic moieties functionalized with bis(trialkoxysilyl) units. These organically-bridged polysilsesquioxanes are unique in that they allow for "simultaneous" formation of both organic and inorganic networks.;Chapter 2 examines the transition from a pure silicate to hybrid material. Silica and methylene-bridged polysilsesquioxanes were compared in solution phase, as well as, in solid state. The solution phase chemistry was studied using mass spectrometric analysis of the polymerization reactions. Analysis revealed similarities in reaction intermediates for the silica and methylene-bridged sol-gel solutions. In addition, analysis of the resulting materials' surface area and porosity showed a striking similarity between the two materials. The importance of precursor on the overall morphology is discussed.;Chapter 3 details the design of thermally labile organic bridging groups. One strategy was to incorporate the carbonate functionality within the inorganic matrix. Dialkylenecarbonate polysilsesquioxanes were prepared and their thermal properties were examined. These materials can undergo thermally induced decarboxylation at 300--350°C. It was revealed that residual silanol groups within the hybrid material can affect the mechanism for decarboxylation.;Chapter 4 discusses the design and synthesis of metal templating sol-gel monomers containing bipyridyl ligands. The goal was demonstrate metal templating by incorporation of a strong coordinating ligand as the organic spacer. The synthesis of the triethoxysilyl functionalized bipyridine ligands was achieved and preparation of metal complexes were also studied.;Chapter 5 illustrates the use of bridged polysilsesquioxanes as effective heavy metal adsorbents. These adsorbents are made by copolymerization of 3-mercaptopropyltriethoxysilane and 1,4-bis(triethoxysilyl)benzene. The resulting materials show high uptake for Hg+2 ions from aqueous solutions. This adsorption capacity is currently one of the highest recorded for any functionalized silicate material. Additionally, new strategies were explored with monomers that contain a disulfide bridge. The disulfide bridge serves as a surrogate for thiol groups. Reduction of the disulfide bridge was preformed in an attempt to liberate the functional thiol group. The potential adsorption capacities afforded to these materials is expected to be substantially improved over existing technology.