| dc.description.abstract | The extended bond length and bond angle of the Si-O linkage yields molecules with properties far different that their carbon analogues—alcohols and ethers. Particularly, Si-O bonds exhibit depressed basicity despite the higher electropositivity of silicon to carbon, giving Si-O bonds good chemical inertness and leading to applications in organic synthesis and industrially significant siloxane polymers. In this study, Si-O bond formation is investigated from Si-H precursors along with siloxane polymers to fabricate novel siloxane molecules and structures. Chapter 1 focuses on silicon-oxygen bond formation by base catalyzed dehydrogenation between silanes and hydroxyl groups. The dehydrogenation of diphenylsilane, a highly reactive silane species with two reactive hydrogens, was the silane of interest. Various catalyst types were explored for facilitating the reaction including three hydroxides, six amines, and an N-heterocyclic carbene-copper alkoxide complex (CuIPr-NHC). Reactions were monitored via FTIR to observe stepwise consumption of both Si-H bonds in diphenylsilane in the presence of water and various alcohols. Hydroxide catalysts with sodium, potassium, and tetramethylammonium (TMA) cations showed strong dependence of cation identity on reaction rate and observable rate order but did not lead to accumulation of a once-oxidized silane. Amine catalysts exhibited varying levels selectivity to the once oxidized silane, leading to accumulation of diphenylsilanol and hydride terminated oligomers with relative reaction rates seemingly dependent on the size of alkyl substituents. Uniquely, CuIPr-NHC showed very limited reactivity to the second dehydrogenation step. Leveraging this, the production of diphenyl(monoalkoxy)silanes has been demonstrated with primary and secondary alcohols with CuIPr-NHC and alkoxide base activators. Chapter 2 focuses on the continuous production of PDMS microspheres using microfluidics and premix emulsification. Generally, traditional microfluidics are used for this process with unparalleled control over microsphere size and distribution at the tradeoff of low throughput (100s of µL/hr). Using an easily replicated membrane system, premix emulsification is demonstrated to be a viable alternative with reasonable control over microsphere size and polydispersity. Four different membranes were chosen to demonstrate system capabilities, with median microspheres dimeters ranging from 5 to 45 µm. Chapter 3 leverages the topics of Chapter 1 and Chapter 2. Base catalyzed dehydrogenation is applied as a method for interfacial polymerization to stabilize W/O/W double emulsions and to produce PDMS microfoam structures. Dehydrogenation of poly(dimethyl, methylhydro siloxane) with polyethylene glycol effectively forms amphiphilic co-polymer networks that function as surfactants at water-PDMS interfaces. The interfacial reaction is applied as a means of encapsulating water cores inside of PDMS microspheres. This method was found to be an improvement over the use of non-reactive silicone emulsifiers for forming double emulsion microspheres during high shear emulsification processes, however droplet breakup for microspheres under 50 µm becomes difficult. The interfacial reaction also produced high amounts of hydrogen gas, which can be captured within nascent microspheres yielding a high internal phase with tunable mechanical properties. | |
