Microemulsions are nanostructured dispersions that have unique properties, which make them attractive for applications such as biomaterials, drug delivery, and nanoparticle synthesis. The behaviour of hydrocarbon microemulsions and their applications have been extensively studied, however, there have been very few studies in the preparation or the polymerization of silicone microemulsions. Silicone microemulsions offer a unique template by which to create novel nanoporous silicone elastomers and/or hydrogels. The prevalent use of silicones in biomaterials, coatings, and personal care (to name a few) make the development of silicone-based microemulsions of particular interest. The aim of thesis research was to polymerize silicone microemulsions and to understand the factors that contribute to retaining initial template morphology in the polymeric product. Chapter Two of this thesis focuses on the preparation of silicone microemulsions containing a non-polymerizable and polymerizable trisiloxane surfactant, respectively. Formulations were prepared and characterized by electrical conductivity to determine the microemulsion structure type. Formulations located in the bicontinuous region of the phase diagram were polymerized, producing transparent silicone elastomers. The focus of Chapter Three was to determine the tolerance of silicone microemulsions to selected chemistry that is relevant to silicone polymers. Previous work done in the field of polymerizing silicone microemulsions has been based on radical polymerization processes. There are no reports that examine the polymerization of a silicone microemulsion by room temperature vulcanization (RTV), a common process for creating silicone elastomers. We aimed to better understand the effects of RTV cure on morphology retention from the liquid to polymeric product to determine if this type of chemistry could be used in the formation of nanoporous silicone elastomers either on its own or in conjunction with a radical polymerization process. In order to understand the effects of an RTV process on polymer structure, we examined the effect of the variable components (necessary for the RTV cure) on the silicone microemulsion template. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used as tools to characterize materials prior to and after cure. Silicone microemulsions that were cured using the RTV process produced nanoporous polymeric elastomers, however, the initial bicontinuous microemulsion template was not retained. RTV cured microemulsions retained the bicontinuous structure if the RTV cure was preceded by a photopolymerization reaction to “lock-in” surfactant monomers at the oil/water interface. Chapter Four explores the use of silicone microemulsions as a reaction vehicle in the formation of nano-TiO2 particles. The focus of this chapter was the exploitation of microemulsion droplets and bicontinuous structures that were designed to retard TiO2 particle formation in situ. Titanium isopropoxide (TTIP) was incorporated into silicone microemulsions containing varying amounts of water. Interactions between TTIP and the trisiloxane polyether surfactant result in the formation of a compound containing a Ti4+, coordinated to silicone surfactant molecules via a polyether linkage. Titania forms in situ as water is titrated into the surfactant/oil mixture, resulting in the formation of a microemulsion. The formation of TiO2 was monitored by UV-Vis spectroscopy and the TiO2 particles were characterized using transmission electron microscopy. / Thesis / Doctor of Philosophy (PhD) / This thesis is about the chemical modification and polymerization of nanostructured liquids in the form of silicone microemulsions to create nanoporous silicone elastomers (nano is one billionth, 10-9, so 1 nanometer = 1 billionth of meter). Despite the highly prevalent commercial use of silicones and the utility of silicone elastomers, little is known about the polymerization of silicone microemulsions to create nanoporous materials. The first goal of this thesis was to polymerize silicone microemulsions, using methods that have been previously used in the polymerization of hydrocarbon microemulsions. Silicone microemulsions were successfully polymerized using a reactive surfactant and rigidification of the oil phase was achieved using common silicone crosslinking chemistry. The second goal was to understand how the type of chemistry affects changes in structure upon transition from liquid microemulsion to solid polymer. Nanostructuring was retained in polymerized microemulsions both with and without oil phase polymerization. Finally, the third goal was to exploit silicone microemulsion domains to control titanium dioxide particle formation. Particle formation was slowed as a result of domain constricted particle growth.

<p> Nonaqueous poly(methyl methacrylate) latices were prepared by nonaqueous dispersion polymerization of poly(methyl methacrylate) in heptane in the presence of either trimethylsilyl terminated or vinyl terminated polydimethylsiloxane stabilizer. Poly(methyl methacrylate) particles stabilized by vinyl terminated polydimethylsiloxane showed smaller particle sizes than did those stabilized by trimethylsilyl terminated polydimethylsiloxane. Diameters of the various latex preparations ranged from 1.4 to 0.8 μm and silicone content was around 2 mole percent in each case. Differences between the two types of latex were explained in terms of the nucleation mechanism operating during the preparation of the latices and in terms of the type of attachment of the stabilizer chain to the poly(methyl methacrylate) core.</p> <p> The effect of the silicone concentration present during particle formation was investigated. Vinyl terminated polydimethylsiloxane stabilized latex gave better stabilized particles than did methyl terminated polydimethylsiloxane stabilized latex. The results of varying the concentration and type of initiator were consistent with the conclusions about differences in nucleation and grafting mechanisms.</p> <p> The stability of polydimethylsiloxane stabilized poly(methyl methacrylate) particles was investigated in n-heptane. Acidified montmorillonite clay was determined as the optimum catalyst for this latex system. Flocculation set in at 70% of the original silicone content when the siloxane on the particle surface was degraded with montmorillonite clay in a good solvent. Flocculation was irreversible and occurred abruptly. The point of flocculation was reproducible and the rate of flocculation was identical for two different types of silicone stabilized poly(methyl methacrylate) latex.</p> / Thesis / Master of Science (MSc)

<p> This thesis provides examples of new Si-based polymeric materials in three parts. The rapid evolution of hydrogen gas was observed after the combination of an α- or β-hydroxy carboxylic acid with an alkoxyhydrosilane. This unusual reactivity is interpreted to arise from the cooperative nucleophilic attack of the hydroxy group at silicon and the electrophilic attack of the acid proton at the Si-H bond. These systems further react to produce modified sol-gel materials in which the acid units were incorporated into the matrix.</p> <p> The reactions of tetraethoxysilane, (TEOS) and α-hydroxy acids similarly produced modified sol-gels (in solution, DMSO) and solids (precipitated from THF). The reaction kinetics were followed in these systems using 29Si NMR. Extensive characterisation of our sol-gels was carried out by the use of various NMR techniques, FT-IR, elemental analysis and thermal methods of solids characterisation (TGA, DTA, and DSC).</p> <p> Silicones containing vinylsilane units were prepared in order to examine the silicon β-effect in a polymeric system for the first time. The addition of bromine to these systems unexpectedly resulted in no reaction unless vigorous conditions were used. Steric factors as shown by molecular modeling are attributed to this lack of reactivity. Although many silicone systems were studied where more sterically "open" vinylsilanes were present these steric problems could not be overcome.</p> / Thesis / Master of Science (MSc)

<p> This thesis presents a study of the compatiblization of a hydrophobic, synthetic polymer, polydimethylsiloxane (PDMS) and a hydrophilic biopolymer, starch. The Diels- Alder adduct of cyclopentadiene and maleic anhydride, bicyclo[2.2.1]hept-5-ene-2,3- dicarboxylic-anhydride, (1), was hydrosilylated with hydride- terminated PDMS to yield α,ω-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic-anhydride-polydimethylsiloxane, (4) having an average molecular weight of 750 g mol^-1. This was then reacted with starch using dimethylaminopyridine as a catalyst in a dimethylsulfoxide medium at 80°C to yield a silicone-starch graft copolymer having a γ-carboxylic-ester linkage.</p> <p> In order to study the influences of the quantity of hydrophobic and hydrophilic components, a series of composites were synthesized varying the starch and silicone stoichiometry (series-1).</p> <p> In order to study the influence of the molecular weight of the silicone, 4 was redistributed with octamethylcyclotetrasiloxane (D4) via cationic polymerization to yield higher molecular weight derivatives. The products were 7 (1500 g mol^-1) and 8 (9000 g mol^-1). These were reacted with starch to give a series of composites for each molecular weight of the functionalized silicone.</p> <p> Spectroscopic and physical properties were analyzed for developing trends.</p> / Thesis / Master of Science (MSc)

<p> Attempts to prepare silicone oligonucleotide copolymers are complicated by the large difference in hydrophobicity in the two materials. Two approaches were followed to overcome this challenge. Initially, highly sterically hindered tetraisopropyldisiloxanes were used to bind 5'-0-(4,4'-dimethoxytrityl)-thyrnidine at the 5'-0H. These compounds proved to be hydrolytically more stable than the analogous dimethylsiloxane compounds, which were also prepared. Alternatively, Si-C bonds, which are hydrolytically stable, can be used to bind the two species together. Introduction of allyl ether by traditional Williamson conditions was followed by hydrosilylation with hydride terminated (Si-H) silicone, catalyzed by using platinum complexes, to give the nucleoside-functionalized silicone. We also introduced an epoxy group to one end of a silicone chain and found it to be stable to hydrolysis. Once the epoxy group binds nucleoside-functionalized silicone to solid phase, it is expected that the nucleoside-functionalized silicone via a trimethylene spacer linkage might be a starter for preparation of oligonucleotide-functionalized silicones in future work. </p> / Thesis / Master of Science (MSc)

The pursuit of optimizing soft contact lens performance has been extensive, given that approximately over 140 million contact lens wearers globally seek the convenience and visual acuity they offer. However, a persistent challenge is the prevalence of ocular dryness and discomfort experienced by almost half of these wearers, particularly towards the end of the day. The occurrence of these symptoms is primarily attributed to diminished compatibility between the contact lens and the ocular surface leading to contact lens discontinuation. A promising method to improve overall contact lens properties is to incorporate novel monomers with unique functionalities during the initial manufacturing stage. Monomers bearing ionic functional groups have been extensively explored to improve bulk and surface properties of biomaterials. The incorporation of cationic and zwitterionic monomers in the fabrication of hydrogel materials has shown to have anti-fouling and anti-bacterial properties and improved surface wetting. In this work, a series of novel materials using cationic and zwitterionic monomers were prepared and their impact on bulk and surface properties of contact lens materials were assessed. Furthermore, the impact of a novel hydrophilic silicone-based monomer bearing zwitterionic phosphocholine was investigated for water-based extraction, physiochemical and structural stability in candidate contact lens materials. In Chapter 2, a library of eleven positively charged (cationic) and electrically neutral with both positive and negative charges (zwitterionic) functional methacrylate ester monomers was produced through the reaction of 2-(dimethylamino) ethyl methacrylate (DMAEMA) with different alkyl halides. The Menshutkin reaction was carried out with a high level of success, resulting in moderate to high yields of the desired monomers. The monomers were purified and characterized using analytical techniques, including 1H-NMR (proton nuclear magnetic resonance), 13C-NMR (carbon-13 nuclear magnetic resonance), LCMS (liquid chromatography-mass spectrometry), and XRD (X-ray diffraction). Six monomers were chosen based on controlled end group hydrophilicity and chain length to investigate the relationship between chemical structure and overall performance in hydrogel and silicone hydrogel systems. In Chapters 3 and 4, model hydrogel and silicone hydrogel systems via UV free-radical polymerization at increasing input concentrations (10 and 20 wt%) were manufactured using the monomers and HEMA (hydrogel) or HEMA + SIGMA (silicone hydrogel). The novel materials demonstrated an increase in bulk equilibrium water content, reduced contact angle and nonspecific lysozyme and albumin adsorption, while maintaining optical transparency at higher than 90%. In vitro studies demonstrated the ionically charged hydrogel materials did not show any toxicity to human corneal epithelial cells. In Chapter 5, a super hydrophilic silicone-based SIGMAPC monomer was synthesized using the siloxane functional monomer (SIGMA) as the main building block. The introduction of the novel hydrophilic SIGMAPC monomer led to significant improvements in the silicone materials. The hydrogels showed increased water content and reduced water contact angles, indicating their superior hydrophilicity. Moreover, the rate of dehydration was decreased, and the nonspecific deposition of lysozyme and albumin was minimized. Importantly, the optical transparency of the hydrogel silicone remained above 90%. Based on these findings, it can be concluded that the siloxane-based monomer bearing a zwitterionic phosphocholine has great potential for applications in contact lenses, given its desirable properties and biocompatibility. Furthermore, in Chapter 6, 31P-NMR and weight extraction analysis showed model contact lens materials made with SIGMAPC were effectively extracted in aqueous media at elevated temperature. Candidate materials showed good dimensional and optical stability pre- and post-thermal sterilization and over 6-month storage period. / Thesis / Doctor of Philosophy (PhD)

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No description available.

Both the thermal and copper(I) catalyzed azide-alkyne Huisgen cycloadditions were explored as strategies to be used for silicone functionalization and crosslinking. The generality of these reactions was demonstrated (Chapter 2) using 1,3-bis(azidopropyl)tetramethyldisiloxane (BAPTMDS) as a model compound. The ligation of this compound with several alkyne-containing molecules, especially the copper(I) catalyzed process or “click” proved to be easy to perform, high yielding, and gave the 1,4-triazole regioisomer as the sole product. Thermal, metal catalyst-free, azide-alkyne cross-linking (Chapter 3) using a poly(azidopropylmethylsiloxane)-co-dimethylsiloxane as the base polymer and several polysubstituted alkyne molecules as crosslinkers was efficient. The reaction of the base polymer with an ethynyl-terminated disiloxane demonstrates that a silicone elastomer can be synthesized by simple heating and that the resulting material is stable, decomposing only at temperatures higher than 230 °C. Finally, direct bioconjugation of silicones to biotin using propargylamide and BAPTMDS was examined (Chapter 4). The result of the copper(I) catalyzed Huisgen ligation of biotin onto silicones was as efficient as the reactions in the previous chapters, revealing that the “click” process can successfully be applied to a broad range of silicones. / Thesis / Master of Science (MSc)

No description available.