Synthesis and characterization of polyoligosiloxysilicones

Promovendus/a: Sam Smet

Promotor(en): Prof. dr. ir. Johan Martens

Silicon-based materials are of vital importance in today’s society. From the sand and clay dug up from the Earth to be used in construction, to the highly purified forms used in the production of electronics, computers and medical implants, the chemical element Si has found its way into nearly every aspect of our lives. Nevertheless, our highly technological world is fueled by an ever-lasting quest for progress. This search continuously increases the demand for new materials with improved or new properties. One imaginative approach towards novel material design and synthesis starts from relatively small molecular building blocks that can be combined in ingenious ways to create highly specialized compounds. Within the world of silicon-based materials the cubic oligomer [Si8O12], also known as the double four ring (D4R), is seen by many as such a potential building block.

Up until now some attempts have been made in connecting D4R units in a controllable fashion, one of which by the connection with silicone linkers. Some of the reported materials were synthesized by reacting bifunctional silanes with the D4R units of a cyclosilicate hydrate. The large amounts of water molecules present in previously available D4R sources, however, rendered controlling the length of the silicone linkers very difficult, due to undesired side reactions of the silane reagent with water. Cyclosilicate hydrate chemistry does, however, provide hints at lowering the water content in the precursor material. Cyclosilicate hydrate structures made in the presence of hexamethyleneimine or tetrabutylammonium hydroxide both consist out of hydrogen bonded D4R units and contain much less water compared to conventionally used D4R sources. In this doctoral research, the possibility of using these alternative precursor materials as D4R source to synthesize D4R-silicone copolymers while exerting some control on the length of the connecting silicone linkers, was investigated. This approach has proven succesful and the resulting copolymers are referred to as polyoligosiloxysilicones, or POSiSils in short.

This work has opened the way to the new family of POSiSil materials, situated next to existing families of nanoporous materials such as zeolites and metalorganic frameworks (MOFs). The variability of cyclosilicate and linkers makes the POSiSil family potentially as large as the latter families. By applying the principles of network design, a near infinite amount of members of this new class of materials can in principle be made available for application.