Doctor of Philosophy (Ph.D.), Bowling Green State University, 2024, Photochemical Sciences

R-alkoxysilanes are the monomer workhorses of silicon-based sol-gel chemistry and are used as the building blocks for materials from silicas to silicones. However, since their inception, the sol-gel and siloxanes communities have struggled with uncontrolled hydrolysis, premature condensation, and overall polymerization and functionalization control. This dissertation focuses on the development of new silicon sol-gel chemistry methodologies which utilize photocaged R-alkoxysilanes and siloxane polymers to aid in synthetic control towards distinct silicon-based materials. We started our investigation with the synthesis and characterization of 2-nitrobenzyloxy photocage systems from ethyl and phenyl derivatives of Rx-(alkoxy)silanes, with x=0-3 and y=1-4, end group photocaged polydimethylsiloxanes, as well as photocaged polyhedral oligomeric silicon-based cage systems. Furthermore, we have also developed Rx-(alkoxy)silanes, with x=0-3 and y=1-4 that contain the 3-dimethylaminobenzyloxy photocage as a more stable alternative to the 2-nitrobenzyloxy based compounds. We have explored the photochemical responses for photo removal including kinetics, efficiency, stability, and tin catalyzed coupling of products to induce polymerization and surface functionalization. We have found that sufficient removal of the photocage groups was achieved, giving a new avenue to generate silicon-based materials. For this dissertation, Chapter 1 describes the background photochemical and silicon-based chemistries needed to understand these processes and their challenges. Chapter 2 details the extensive work on Rx-(alkoxy)silanes containing 2-nitrobenzyloxy groups and their performance in photochemical processes. Chapter 3 defines the work on 2-nitrobenzyloxy polymeric/oligomeric versions of silicon-based materials. Chapter 4 gives an overview of our preliminary work on 3-dimethylaminobenzyloxy photocaged Rx-(alkoxy)silanes. Finally, Chapter 5 gives conclusions and connections for this resea (open full item for complete abstract)

Committee: Joseph Furgal Ph.D. (Committee Chair); Ellen Gorsevski Ph.D. (Other); Jayaraman Sivaguru Ph.D. (Committee Member); Alexander Tarnovsky Ph.D. (Committee Member) Subjects: Chemistry; Organic Chemistry

MS, University of Cincinnati, 2019, Engineering and Applied Science: Materials Science

This research is focused on investigating the effect of ex-situ addition of Graphene (GR) on rheological, structural, mechanical and electrochemical properties of Polyimide/Poly (dimethyl siloxane) (PI/PDMS) copolymer. The composite is thereby characterized for electrochemical energy storage applications. Graphene-based polymers are widely being researched as high-performance electrode materials for supercapacitor and battery applications due to their unique properties such as high current density, high thermal conductivity and excellent mechanical behavior. PI/PDMS is a copolymer that combines the high thermal stability and chemical resistance of PI with excellent flexibility and hydrophobicity of PDMS. Herein, the performance of this flexible thin film nanocomposite as an electrode material with optimum graphene loading is evaluated and reported.

Committee: Jude Iroh Ph.D. (Committee Chair); Je-Hyeong Bahk Ph.D. (Committee Member); Woo Kyun Kim Ph.D. (Committee Member) Subjects: Engineering

Doctor of Philosophy, University of Akron, 2017, Polymer Engineering

Alkyd Resins are a class of seed-oil based polyesters used in the coatings industry for solventborne architectural and wood coatings, but are inferior in performance to petroleum-based resins. Solventborne coatings contain large quantities of volatile organic compounds (VOCs), which contribute to hazardous emissions. Another major drawback is the slow autoxidative crosslinking mechanism, which is catalyzed by toxic cobalt driers. This work targets the three major drawbacks of alkyds to develop high performance and high solids alkyds with improved drying times. In the first part, triethoxysilane modified alkyds were prepared as an additive to medium linseed oil alkyd. The alkoxysilane forms covalent bonds with oxidized metal substrates, improving coating's adhesion. The low surface energy of silicon shifted the contact angle from hydrophilic to hydrophobic surface wetting, leading to improved coating properties in comparison to an alkyd control. The corrosion resistance was examined with electrochemical impedance spectroscopy, unexpectedly showing an increase in barrier performance when immersed in a 3.5 wt.% NaCl solution. Solid-state 29Si NMR spectroscopy detected a structural change in coatings immersed in salt solution, forming more crosslinked siloxane networks. In the second part, a fluorinated linseed oil alkyd (FLOA) with a fluorinated repeat unit in the polyester backbone was prepared for anti- graffiti coatings. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) showed the formation of fluorinated domains and a partial migration of fluorine to the coatings surface, thus preserving the coating's adhesion to the substrate. FLOA coatings increased hydrophobicity, coating performance, corrosion resistance, and ultimately graffiti resistance. In the final two sections, visible light-curable alkyds and uralkyds were studied for coatings and adhesives. The use of photoinitiators and a photosensitizer was able to reduce the drying time (open full item for complete abstract)

Committee: Mark Soucek Ph.D. (Advisor); Kevin Cavicchi Ph.D. (Committee Chair); Toshi Miyoshi Ph.D. (Committee Member); Thein Kyu Ph.D. (Committee Member); Wesdemiotis Chrys Ph.D. (Committee Member) Subjects: Chemistry; Polymer Chemistry; Polymers

MS, University of Cincinnati, 2003, Engineering : Materials Science

Inorganic-organic hybrid materials can provide excellent combined properties. And when the length scale of the component phase approaches nanometers, the expected global properties will be more strongly affected by interfacial interactions rather than bulk phase properties. Polyhedral oligomeric silsesquioxane (POSS) is an entirely new inorganic component that has defined structure and functional groups; thus POSS opens the possibility of preparing nanocomposites with controlled morphology and tailored interfaces. POSS systems can be developed to elucidate the effect of the structure and interfacial bonding on polymer microstructure and the resulting effects on macroscopic properties. The first section of this thesis reports the use of monovinyl POSS as a building block to make controlled-structure materials. Four POSS cages with vinyl groups were linked to a central siloxane core using a hydrosilylation reaction. The hydrosilylation reaction was monitored using fourier-transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H-NMR). The resulting structure was confirmed by mass spectroscopy (MALDI-MS). In the second section, POSS was incorporated into poly(dimethylsiloxane) (PDMS) physically and chemically to investigate the effect of polymer-filler bonding. For physically blended composites, single POSS molecules and the molecules with up to four connected POSS (tetraPOSS) were used. The goal was to investigate the size effect on the reinforcement. In the chemically-bonding system, vinyl terminated PDMS was used; therefore, some POSS molecules were attached to the network through the hydrosilylation reaction. Both tensile tests and dynamic mechanical analysis showed that simply blending these POSS-based fillers into silanol-terminated PDMS had little effect on its mechanical properties, but bonding them to the PDMS provided considerable reinforcement. Based on these results, it seems that the reinforcement results not from direct bonding, bu (open full item for complete abstract)

Committee: Dr. Dale W. Schaefer (Advisor) Subjects:

Doctor of Philosophy, Case Western Reserve University, 1994, Chemistry

Long chain trichlorosilyl terminated surfactants have been used to modify surfaces of different substrates such as Si, Ge, and ZnSe by forming self-assembled monolayers on these surfaces. Four different kinds of studies of these systems are described in this thesis: (i) The kinetics for the formation of an alkylsiloxane monolayer film is monitored by FTIR-ATR and a Langmuirian model has been used to fit the FTIR-ATR results. The Langmuirian model indicates that the rate of film formation is proportional to the unoccupied sites available for the surfactant molecules. (ii) Surfaces coated with monolayers containing ω-carboxylic acid groups have been developed. The ionization of carboxylic acid groups bound to the surface is studied by in situ FTIR-ATR. The results indicate that the extent of ionization of the surface and near-surface carboxylic acid groups at a given pH differs from that in bulk-phase liquid and the carboxylic acid groups become less acidic when packed on the surface. A model based on the neutral oligomer of the acid groups is used to fit the in situ FTIR-ATR results. (iii) A series of fluoroketone and fluoroalcohol modified surfaces have been created. The wetting properties of these monolayer coated surfaces are characterized by contact angle measurements and ex situ FTIR-ATR. The relative reduction rates of the carbonyl groups in ho mogeneous solution are compared to those of the self-assembled monolayers. (iv) Self-assembled monolayers have shown potential as coatings for biomaterials for implants. Previous studies suggested that surfaces with different compositions modulate the conformation of fibronectin and thus affect the differentiation response of fibroblasts and neuronal cells in a cell type-specific pattern.32-34 Using aqueous FTIR-ATR we have directly evaluated that the conformation of adsorbed fibronectin depends on the composition of the self-assembled monolayer coating. Our results clearly demonstrate a surface dependent conformational (open full item for complete abstract)

Committee: Chaim Sukenik (Advisor) Subjects: Chemistry, Organic

Doctor of Philosophy, Case Western Reserve University, 1990, Chemistry

Long chain trichlorosilyl terminated surfactants containing ω-functional groups have been used to form siloxy-anchored self-assembled monolayers on various substrates including glass, Si, Ti, Ge and ZnSe. The functional groups used are Br, SCN, CN, SCOCH3 and CnF2n + 1CO (n = 1-3). The conditions for the formation of these monolayers have been determined and they have been characterized by contact angle measurements, attenuated total reflection IR spectroscopy and X-ray photoelectron spectroscopy. The stability of these monolayers under different environments has been assessed. In situ chemical transformations of these monolayers have led to the generation of a new set of monolayers with different functional groups at the surface. Among these new monolayers are many that are not accessible by direct surfactant deposition. A variety of successful SN2 displacement reactions have been achieved at the surface of a well packed monolayer. Different starting surfaces and different reaction pathways have been used to arrive at the same surfaces as a crosscheck of the composition and integrity of these functionalized monolayers. Amine containing surfaces have been generated by in situ chemical transformations. This was achieved by transforming the Br terminated surface to the azide followed by its reduction or by the reduction of a directly deposited nitrile surface. A series of sulfur containing surfaces have been generated either by direct deposition or by in situ chemical transformations. The sulfur containing surfaces are -SH, -SCN, -SCOCH3, -S-S-, -S- -(SO2)- and -SO3H. This work has demonstrated the feasibility of carrying out surface transformations using bidentate nucleophiles (S-2 and S2-2) to generate functional groups bridging neighboring alkyl chains of the monolayer. In a different study, using monolayers formed from fluoroketone surfactants, two issues have been addressed. The influence of polar groups 2 to 4 carbon atoms deep from the surface, on the wettin (open full item for complete abstract)

Committee: Chaim Sukenik (Advisor) Subjects: Chemistry, Organic

Doctor of Philosophy, Case Western Reserve University, 1994, Macromolecular Science

Polydiarylsiloxanes are highly crystalline, high melting polymers with excellent high temperature properties. The polymers of greatest interest in this investigation have been those containing phenyl and p-tolyl substituents on the siloxane backbone. We have prepared a series of polymers with various combinations of these substituents, as well as the end members of the series, polydiphenylsiloxane and polydi(p-tolyl)siloxane. The polymers are prepared with controlled molecular weights and distribution by ring-opening anionic polymerization of the cyclic trimers in solution. The crystal ightarrow liquid crystal transition temperatures Tlc, for polydiphenylsiloxane and polydi(p-tolyl)siloxane are very high (265°C and 300°C, respectively) and the polymers are only soluble in a few solvents at temperatures above 150°C. However, the liquid crystal transition temperatures are reduced for the mixed poly(phenyl/p-tolyl)siloxanes and the polymers become soluble at lower temperatures. The replacement of a single phenyl group by a methyl group in the repeat hexaphenyl triad sequence of polydiphenylsiloxane is sufficient to destroy both the crystalline and liquid crystalline character of the polymer. The solution properties of three different types of poly(phenyl/p-tolyl)siloxanes have been investigated in order to characterize the chain stiffness properties. The Mark-Houwink-Sakurada exponents, "a", for these polymers are between 0.75 and 0.86. The values of these exponents are below the values expected for a rigid chain (a > 1.0) but are at the upper end or above the values expected for a flexible random coil polymer in a good solvent. The values indicated that the configuration of these polymers in solution is most likely that of a random coil, but with a relatively large persistence length. In addition to the phenyl and p-tolyl siloxane polymers, other diarylsiloxane polymers have been synthesized and characterized. The crystal ightarrow liquid crystal transition temperat (open full item for complete abstract)

Committee: Alexander Jamieson (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2005, Polymer Science

The objective of this research was the syntheses of three types of novel networks by the polymerization of cyclic siloxanes and to study the networks' properties. Earlier work by Kurian and Kennedy in the area of designed membranes led to the synthesis of a novel series of amphiphilic networks for potential biological/medical applications. These networks were prepared by the use of di-vinyl telechelic polydimethylsiloxane, di-allyl telechelic poly(ethylene glycol), and a cyclic crosslinker/reinforcing agent, pentamethylcyclopentasiloxane (D5H). The networks' ability to simultaneously combine a series of demanding requirements for implantation, including biocompatibility, and the exclusion of large defensive proteins while allowing rapid diffusion of smaller proteins/molecules, were investigated in this work. Recently we designed, synthesized and characterized a novel family of siloxane-based polymers, termed cyclolinear polysiloxanes (CLPSs). CLPSs are polymers that contain cyclic siloxane units covalently connected to form linear chains. The cyclic units we designed and used to prepare polymers are diacetoxy-diethyltetramethylcyclotetrasiloxane and diacetoxy-triethylpentamethylcyclopentasiloxane. These novel monomers were catalytically condensed with water to form CLPSs with vinyl termi, and were co-condensed with di-hydroxyl telechelic PDMS to form extended CLPSs (eCLPSs) with PDMS spacers between the cyclic units. Divinyl CLPSs were crosslinked by hydrosilation, and the oxygen permeabilities and mechanical/ thermal properties of the networks were investigated. Based upon insight gained in this work, we developed a new polymerization/curing strategy for PDMS. This strategy involved synthesizing PDMS by ring opening polymerization of a cyclic siloxane (D4) while simultaneously copolymerizing it with our novel eCLPS. Thus, the cyclic units in the eCLPS function as crosslinking agents for the siloxane network. The properties of these siloxane networks were controlled (open full item for complete abstract)

Committee: Joseph Kennedy (Advisor) Subjects: Chemistry, Polymer