<p> The advantageous properties of siloxanes find use in a wide range of
applications. Unfortunately, the dynamic nature of silicones which is responsible for these properties is often a limitation in the controlled synthesis and modification of siloxane materials. Gaining greater control over these processes would allow for the synthesis of siloxane materials with more explicit structures, giving them a narrower range of properties and expanding application. Furthermore, the ability to synthesize more siloxane architectures with greater control would allow for an increased understanding of the relationship between structural features and physical properties.</p> <p> The synthesis of hydrosilane-rich siloxane elastomers and subsequent
controlled modification, particularly with poly(ethylene oxide), is described. The effect of chain length and functionality (mono- or di-) was found to influence the morphology of grafted polymer. It was also possible to take advantage of the intrinsic properties of siloxanes to sequester hydrophilic moieties to the interior of the elastomer. Utilizing the same hydrosilane rich elastomers, a method for the independent modification of the interior and exterior of hydrosilane rich elastomers is presented. The careful selection of grafting moieties and solvents is used to provide or deny transport to the interior of the elastomer. This method is used to synthesize PEO modified elastomers with various subsequent internal modifications.</p> <p> A method for controlled synthesis of silicone-carbohydrate composites is
also described. Utilizing bifunctional silane linkers, protected carbohydrates were functionalized with bulky diisopropyl hydrosilane groups before linkage to short and long silicones. Alternatively, the linker could first be joined to a silicone, followed by silylation of unprotected saccharides using the resultant hindered chlorosilane functional silicone. This method gave preferential silylation at primary hydroxyl groups.</p> <p> Finally, a method is presented for the synthesis of explicit branched siloxane architectures. The B(C6F5)3 catalyzed dehydrocarbonative coupling of hydrosilanes with alkoxysilanes was used to construct branched siloxane architectures in a stepwise fashion. High levels of control were available through manipulation of steric parameters: careful selection of starting materials and conditions allowed for the synthesis of explicit alkoxysilane functional branched siloxanes. These could be grafted to hydrosilane functional silicone polymers, or used to assemble explicit branched siloxanes. Further explorations demonstrated that the assembly process was not inhibited by the presence of organohalide- or alkene functional groups, allowing for the synthesis of functional siloxane moieties with explicit structures.</p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/16841 |
| Date | January 2008 |
| Creators | Thompson, David B. |
| Contributors | Brook, Michael A., Chemistry |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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