Synthesis and characterization of octasilsesquioxane-based molecular composite precursors with potential applications as dental restoratives.

摘要

This dissertation describes the synthesis and characterization of novel molecular composite precursors based on octahedral octasilsesquioxanes (‘cubes’), liquid crystalline (LC), and/or polymerizable functionalities, such as methacrylates and epoxides. These composite precursors as shown below are designed for further polymerization to provide dental materials.*; With the objective of making octasilsesquioxane (‘cube’) based molecular composites, ‘simple cubes’—octasilsesquioxane (H₈Si₈O₁₂, T₈H), octavinylsilsesquioxane (vinyl₈Si₈O₁₂, T ₈V), octakis(dimethylsiloxy)octasilsesquioxane [(HSiMe ₂O)₈Si₈O₁₂, Q₈M₈ H], and octakis(vinyldimethylsiloxy)octasilsesquioxane [(vinylSiMe ₂O)₈Si₈O₁₂, Q₈M₈ V] were first prepared to provide starting materials. Baseline materials were obtained through the hydrosilylation of the Si-H and vinyl functionalized cubes to give cross-linked composite materials. These materials offer very high surface areas (380–530 m2/g), and controlled porosity (1–50 nm).; Epoxy cubes, diepoxyhexavinyloctasilsesquioxane (epoxy₂vinyl ₆Si₈O₁₂, T₂ET₆ V) and octakis(epoxydimethylsiloxy)octasilsesquioxane [(epoxySiMe₂O)₈Si₈O₁₂, Q ₈M₈E) were prepared through epoxidation of vinyl cubes T₈V and Q₈M₈ V using m-chloroperoxybenzoic acid (m-CPBA). The resultant epoxy cubes readily polymerize in the presence of Lewis acids into crosslinked materials.; Methacrylate groups were also bonded to cubes via hydroxyl-functionalized cube, octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane (OHPS) to obtain octakis(3-methacryloxypropyldimethylsiloxy)octasilsesquioxane (OMPS). OMPS prepared in this study is a slightly viscous liquid that readily cures under blue light into a cross-linked composite material.; Four allyloxy functionalized LC mesogens were synthesized and attached to cube Q₈M₈H through Pt catalyzed hydrosilylation of the allyloxy moieties to obtain penta-LC-cubes. LC behavior of the LC-cubes was studied using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction analyses. Three of the four LC-cubes exhibit nematic and smectic A phases, with the lowest melting point at 90°C.; In summary, the synthesis and characterization of octasilsesquioxane based composite precursors have been explored in this work. Both LC mesogens and methacrylates were attached to Q₈M₈H cube successfully, to provide LC-cubes and methacrylate-cubes, respectively. However, the combination of both functionalities on the same cube to prepare polymerizable LC-cubes remains to be done, and their potential application as dental materials remains to be studied.; *Please refer to dissertation for diagram.