Synthesis and investigation of silsesquioxane networks from static to photoactive smart materials

Materials Chemistry is an extremely important area of science touching everything from solar energy conversion to medical implants. The work of this dissertation has focused on developing porous materials, especially related to functional and stimuli responsive materials, including photochemical, for a variety of applications such as environmental remediation, soft robotics, and self-healing materials. We aimed to create silicon-based materials to overcome many of the technological barriers including low thermal stability, low selectivity, and poor mechanical properties of the typical materials used in these types of applications. Chapter 1 gives an overview and background of the types of materials that will be investigated in this dissertation. We will first introduce silsesquioxane (RSiO1.5)n chemistry, including synthesis methodologies, synthetic challenges and the properties that give reasons for their use. The research detailed in chapters 2 and 3 of this dissertation set out to contribute a new synthetic method for silicon-based porous materials involving fluoride catalyzed polymerization of R-alkoxysilanes. We aimed to gain a fundamental understanding of the reaction parameters and their impact on structure-property relationships in porous silsesquioxane-based gel materials. In chapter 4, we explored the interaction of fluoride with a silica-based cage called octa(dimethylsiloxy)silsesquioxane (Q8M8H). While it was expected that little interaction would occur with Q8M8H it was found that the outer siloxane units undergo rapid self-polymerization in the presence of a fluoride anion catalyst to form complex 3D porous structural network materials with specific surface areas up to 650 m2g-1. In chapter 5, we demonstrate our approach to photoswitchable silicon-based network polymers using Q8M8H as a cubic building block and azobenzene as a photo-actuatable cross-linker. We found that these photoswitchable silsesquioxane/azobenzene hybrid 3D–polymer gels can be effectively synthesized and show reversible photo-dynamic sponge characteristics. Lastly, in chapter 6 we discuss the impact of this work on the field and potential ways it can be moved forward to either gain a more fundamental understanding of reaction processes or greatly improve responsive performance of porous silsesquioxane-based materials