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京都大学 / 新制・課程博士 / 博士(工学) / 甲第23930号 / 工博第5017号 / 新制||工||1783(附属図書館) / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 大嶋 正裕, 教授 山子 茂, 教授 佐野 紀彰 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

<p>A series of bismaleimide and bisfuran monomers were synthesized and then combined to produce thermally reversible polymers. Reversibility was demonstrated through multiple heating and cooling cycles, and verified using ¹H NMR spectroscopy. Variation of the spacer chemistry in the monomers was found to profoundly influence the physical properties of the resulting polymers. A tripodal maleimide and furan system was then synthesized, but it was found that the incorporation of cross-linking into the polymer network did not significantly alter the mechanical properties of the resulting polymers.</p> <p>Dilute solutions of polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends containing PS- or PMMA-functionalized single-walled carbon nanotubes (SWNT) were spin cast and annealed at 180°C for 12 h. Characterization of the annealed films by scanning Raman spectroscopy confirmed that the migration of the nanotubes in the films could be controlled using the appropriate functionality on the nanotubes, thus the PS-functionalized nanotubes were found to migrate to the PS domains, while the PMMA-functionalized nanotubes migrated to the PMMA domains.</p> <p>SWNTs were then functionalized using linear reversible polymers, resulting in significant solubilization of the nanotubes. Heating of this solution resulted in the collapse of the DA polymer, and precipitation of the dissolved nanotubes, illustrating the reversible nature of the polymers, and their influence on carbon nanotube solubilization.</p> / Doctor of Philosophy (PhD)

Teenage childbearing is considered a societal ill, despite the evidence failing to demonstrate a causative link between teenage childbearing and negative consequences for teens or their children. This thesis argues that the strongly held assertion that teenage childbearing is detrimental to teens and society is rooted in racist eugenics theories and histories of reproductive coercion. Today, social scientists, health care providers, and public health professionals develop and celebrate programs that reduce rates of teen pregnancy, particularly programs that provide Long Acting Reversible Contraceptives (LARCs) to teens in marginalized communities. While these efforts are well-intentioned, they fail to recognize their perpetuation of histories of reproductive coercion of young women of color. This paper recommends ways in which the medical community can be better informed and respect reproductive autonomy in caring for teens from marginalized communities. / Urban Bioethics

Silicones elastomers are widely used all over the world due to their unusual properties when compared to their carbon-based counterparts. Synthetic methods for their synthesis are still quite limited and the traditional silicone products are not able to completely meet the requirement for modern materials. Silicone elastomers with customized structures and with higher levels of sustainability will be the research focus for the development of next generation materials. The element sulfur and its functional groups are growing players in modern polymer and materials science, since sulfur reactions are exceptionally versatile. The incorporation of sulfur reactions into the design and preparation of silicone materials can lead to silicones with unique properties for various research interests. Initial exploration was focused on the creation of general and simple methods for 3D printing silicone elastomers using thiol-ene chemistry. However, silicone inks suitable for 3D printing are still quite limited. Photo-initiated thiol-ene chemistry was proposed to design a rapid cure silicone ink for extrusion 3D printing. Unlike other radical reactions, the relatively oxygen insensitive thiol-ene was able to provide the necessary rapid reaction rate and build up the necessary viscosity for practical printing in less than 2 seconds in the presence of air. Various customized silicone structures with different moduli were obtained with a relative fast printing speed. The use of thiol oxidation reactions in the synthesis of silicone elastomers is also demonstrated in this thesis. Reductive cleavage of the resulting disulfide bridge was successfully performed with the presence of hydrosilane and B(C6F5)3 catalyst. Herein, a synthetic method to reversible silicone elastomers based on the disulfide linkage is described. This method could be extended to cleave the disulfide and polysulfide linkage in used automotive rubber materials. Various kinds of sulfur-cured rubbers were successfully devulcanized to polymeric oil. This simple and efficient method could potentially offer a solution for the huge amount of tire waste produced every year. Finally, a new method for preparing thermoplastic silicone elastomers with ionic linkages is reported. A novel dicarboxylic acid-modified silicone was synthesized though thiol-Michael additions. The resulting ionic crosslinked networks were built though the neutralization between carboxylic and amino silicone. Thermoplastic silicone elastomers with unique viscoelastic behavior can be obtained. In summary, the thesis demonstrates that sulfur chemistry is an exceptional synthetic tool for the silicone chemist. / Thesis / Doctor of Philosophy (PhD)

In the early 2000s, hydrogen sulfide (H₂S) was added to the family of molecules known as gasotransmitters, a class of endogenously produced and freely diffusing biological signaling molecules. Since this discovery, biologists and chemists have sought to understand the physiological roles of H₂S and to elucidate the potential benefits of exogenous H₂S delivery. As a result, many synthetic small molecule donor compounds have been created to deliver H₂S in response to various biologically relevant stimuli. Furthermore, macromolecular and supramolecular H₂S donor systems have been created to protect donors in the biological milieu, extend release kinetics, or control H₂S release conditions. Thus, H₂S-donating nanostructures with precisely tuned release rates provide invaluable tools for further investigating the biological roles and therapeutic potential of H₂S. This work describes two polymer micelle systems for the controlled delivery of H₂S. The first system is based on H2S-releasing polymer amphiphiles with varying degrees of a plasticizing comonomer incorporated into the core-forming block. The glass transition temperature of the core-forming block varied predictably with incorporation of the plasticizing comonomer. Accordingly, the half-life of H₂S release decreased from 4.2 h to 0.18 h with increasing core-forming block mobility. The second system is based on H₂S releasing polymer amphiphiles with varying degrees of crosslinking in the core-forming block. The crosslinked system was designed to achieve control over H₂S release rate with minimal dilution of donor in the core-forming block. The half-life of H₂S release increased from 117 min to 210 min with increasing crosslink density in the core-forming block, further demonstrating that H₂S release rates can be precisely controlled by tuning micelle core mobility. Beyond control over H₂S release rate, further study of the biological roles of H₂S requires donor systems with precisely triggered release. To this end, this dissertation also discusses efforts to investigate fundamental micelle–unimer relationships. This section includes an evaluation of the impact of core-forming block mobility on micelle–unimer coexistence utilizing a model polymer amphiphile system. Unimer populations correlated with glass transition temperatures of the core-forming block, suggesting the need to consider micelle core mobility when discussing polymer chain phase behavior of amphiphilic block copolymers. Finally, this work discloses new methods for the radical polymerization of poly(olefin sulfones) with control over molecular weight. POSs are a unique class of polymers with great potential for stimuli-responsive depolymerization to generate sulfur dioxide (SO₂), a signaling gas related to H₂S. / Doctor of Philosophy / Hydrogen sulfide (H2S) is commonly known for its pungent odor and toxicity. Despite this negative stigma, H2S has been revealed as a vital signaling molecule in both plants and animals. This discovery has prompted the coordination of biologists and chemists in an effort to better understand the roles of H2S in the body. Driven by this motive, great interest has centered around the development of finely tuned molecules designed to generate H2S in the body, termed H2S donors. A variety of synthetic H2S donors have been reported with various conditions enabling release. Building on this work, the development of polymeric H2S donors with tunable release rates will enable investigation into the complex behavior of H2S in the body. The first half of this dissertation focuses on the design and synthesis of two polymeric H2S donor systems for the controlled release of H2S. These systems take advantage of sequestering the H2S donating species inside a polymeric nanostructure in water called a micelle. Because H2S release requires a triggering molecule to enter the polymeric nanostructure, release rate can be tuned by modifying the mobility of the structure. The first system discussed demonstrates this concept by increasing the flexibility of the micelle core. As expected, H2S release rates increased with increasing flexibility. The second system discussed advances this idea by limiting mobility within the micelle core, rather than increasing flexibility. Accordingly, H2S release rates decreased with decreasing mobility within the micelle core. The latter half of this dissertation broadly explores the development of polymeric signaling gas delivery vehicles with triggered release conditions. We first investigate the impact of polymer chain flexibility on the formation of micelles in water. Polymer chain flexibility significantly impacted the balance between micelles and unassembled polymer chains in solution, suggesting the need to consider this characteristic when designing donor systems for precise release conditions. Lastly, we discuss the development of controlled polymerization techniques for poly(olefin sulfones). We envision that poly(olefin sulfones) will be a useful class of polymers in the design of donor systems relying on triggered depolymerization for release of the signaling gas sulfur dioxide.

This dissertation describes a general synthetic platform for segmented polymers that have main-chain reversible linkages based on cyclopentadiene-maleimide Diels-Alder chemistry. Research in the area of thermally reversible (self-healing) polymers has been an ever-expanding area of interest in the current scientific literature. However most of the emphasis has been on systems containing furan-maleimide linkages. While inexpensive and synthetically accessible, furan chemistry is mostly limited to crosslinked and hyperbranched architectures due to its relatively weak binding with maleimides at suitable propagation temperatures. Following a general review of the literature in this area (Chapter 1) the first stage of our research (Chapter 2) entails the synthesis of 2-substituted hydroquinones, which are needed as monomers in the later stages. The novelty of our hydroquinone synthesis stems from the use of allylic and other alkenyl ethers as the source of the ring substituent, and from the utilization of catalytic hydroboration to improve atom-efficiency. We showed that hydroquinones with widely varying functionality can be prepared efficiently by our method; these findings were published in the journal Tetrahedron in 2018. The second stage (Chapter 3) involves the use of the new hydroquinones in step-growth syntheses of hydroquinone-terminated telechelic and chain-extension of these telomers via Diels-Alder chemistry to form segmented polymers having thermally reversible linkages. The novelty of our approach rests with the use of cyclopentadiene-maleimide chemistry for the linkages, while the overall physical properties such as the glass transition temperature were established by using well-defined aromatic polymers — poly(ether ether ketones) or PEEK and poly(aryl ether sulfones) or PAES — as segments. This approach represents an important departure from earlier work in our group in which reversible linkages were present in every repeat unit of a step-growth Diels-Alder polymer that showed thermal reversibility in solution but not in the bulk, owing to glass transition temperatures that were too high. Using scratch-healing and mechanical (tensile) tests, we show that our new segmented polymers exhibit self-healing characteristics that are competitive with or superior to previously reported systems based on different Diels-Alder chemistry. The third stage (Chapter 4) aims to explore new application areas for some of the more novel functionalized hydroquinones reported in Chapter 2. First we developed an efficient synthesis of a PAES derivative bearing 5-phenoxypentyl groups on the hydroquinone moiety. Then we showed that the 5-phenoxy group can be cleanly cleaved, post-polymerization, to afford a PAES having 5-bromopentyl substituents. The promise of our method rests with the potential of the pendant electrophiles to undergo reactions with nucleophilic reagents to post-modify these polymers further. As proof of concept, we showed that substitution of the pendant bromides with furfuryloxy groups enabled thermally reversible crosslinking with a bis-maleimide reagent to form a polymeric material that demonstrates partial scratch healing. Finally we are exploring the synthesis of new ion-containing polymers by substituting the pendant bromides with tertiary amines. / PHD / This dissertation describes a new synthetic approach to polymeric materials that can heal themselves (for example, repair small cracks that may have formed due to stress or aging) simply by heating the damaged area. Our approach uses a thermally reversible chemical reaction (called the Diels-Alder reaction) to connect several shorter polymer segments into longer chains. Upon heating, the segments can come apart, diffuse into and through the damaged area, and then rejoin. The first chapter is a review of background in the published literature as well as previous not-yet-published work in our laboratory. The second chapter describes the creation of new building-block molecules (monomers) that will help control the temperature range necessary to induce self-healing after incorporation into the polymer segments. The third chapter details the process of forming the segments, the incorporation of self-healing functionalities on the ends of the segments, the joining of the segments into longer polymeric chains, and the testing of all of the physical properties of these new materials, including their self-healing capabilities. The fourth chapter represents a preliminary study of a new method of preparing ion-containing polymers. The latter materials have potential use in various membrane technologies including fuel cell devices for the harnessing of renewable energy.

Biological development and progression are managed by a diverse macromolecular group called proteins. Protein structure results from a complex folding process that leads to a final active form. This protein state is susceptible to changes in the surrounding environment and an incorrect structure can be produced. Changes in the protein conformation can lead to the formation of protein aggregates. Adsorption of proteins onto surfaces is utilized in many research analyses, but is capable of irreversibly changing the protein structure and causing aggregation. Albumin is a plasma protein that adsorbs on many different surfaces because the structure easily rearranges. The structure of albumin once adsorbed has been shown to deteriorate; however, outcomes of both stabilization and aggregation have been found. A dynamic laser light scattering instrument will be utilized to measure the differences in size and determine the amount of aggregation. Our lab has developed a z-axis translating laser light scattering device (ZATLLS) that has been used to measure the sedimentation velocity of several different materials in solution. In this case, bovine serum albumin (BSA) will be adsorbed onto polystyrene particles and the particle settling velocity determined. The settling solution viscosity and density will also be ascertained, so Stoke's law can infer the average aggregate size of each experiment. BSA-coated polystyrene particles displayed a more controlled settling behavior compared to non-coated polystyrene particles. Although the BSA-coated particles had a smaller sedimentation velocity, a larger aggregate size was found due to the greater solution viscosity. Therefore, the ZATLLS instrument can be employed to measure sedimentation velocities of multiple interactions and the aggregation level inferred. Although most albumin molecules are remarkably similar, there are subtle differences in amino acid residues, length, and charge. Sedimentation velocities for human serum albumin (HSA) coated polystyrene particles and BSA-coated polystyrene particles only had a small difference. However an almost 50% higher solution viscosity was measured in BSA experiment solutions, and resulted in the slower settling of the larger aggregates compared to HSA-coated particles. Viscosity calibration curves for each albumin species were used to determine the amount of protein desorbed from the particles during the settling process. The larger solution viscosity for BSA-coated particle experiments led to a much larger degree of desorption. HSA was shown to be the more stable albumin species when adsorbed onto polystyrene particles. Temperature denaturing was performed to aid in the determination of the stability of BSA. Reversible and irreversible conformational changes in BSA were produced at 46ºC and 76ºC respectively. The solutions were cooled to room temperature before adsorption ontopolystyrene particles and the sedimentation velocities measured. A 50% difference in average viscosity between the reversibly and irreversibly changed BSA was found. This caused the larger aggregates formed in the 76ºC BSA experiments to have an almost equivalent sedimentation velocity to those in the reversibly denatured BSA experiments. Average aggregate size for reversibly denatured BSA was well within the ranges found for non-denatured BSA. In conclusion, irreversibly denatured BSA formed larger aggregates and was more likely to desorb from the polystyrene particles than reversibly changed BSA. / Master of Science

[EN] This thesis addresses the treatment of perturbed problems with splitting methods. After motivating these problems in Chapter 1, we give a thorough introduction in Chapter 2, which includes the objectives, several basic techniques and already existing methods. In Chapter 3, we consider the numerical integration of non-autonomous separable parabolic equations using high order splitting methods with complex coefficients (methods with real coefficients of order greater than two necessarily have negative coefficients). We propose to consider a class of methods that allows us to evaluate all time dependent operators at real values of the time, leading to schemes which are stable and simple to implement. If the system can be considered as the perturbation of an exactly solvable problem and the flow of the dominant part is advanced using real coefficients, it is possible to build highly efficient methods for these problems. We show the performance of this class of methods for several numerical examples and present some new improved schemes. In Chapter 4, we propose splitting methods for the computation of the exponential of perturbed matrices which can be written as the sum A = D+epsilon*B of a sparse and efficiently exponentiable matrix D with sparse exponential exp(D) and a dense matrix epsilon*B which is of small norm in comparison with D. The predominant algorithm is based on scaling the large matrix A by a small number 2^(-s) , which is then exponentiated by efficient Padé or Taylor methods and finally squared in order to obtain an approximation for the full exponential. In this setting, the main portion of the computational cost arises from dense-matrix multiplications and we present a modified squaring which takes advantage of the smallness of the perturbation matrix B in order to reduce the number of squarings necessary. Theoretical results on local error and error propagation for splitting methods are complemented with numerical experiments and show a clear improvement over existing methods when medium precision is sought. In Chapter 5, we consider the numerical integration of the perturbed Hill's equation. Parametric resonances can appear and this property is of great interest in many different physical applications. Usually, the Hill's equations originate from a Hamiltonian function and the fundamental matrix solution is a symplectic matrix. This is a very important property to be preserved by the numerical integrators. In this chapter we present new sixth-and eighth-order symplectic exponential integrators that are tailored to the Hill's equation. The methods are based on an efficient symplectic approximation to the exponential of high dimensional coupled autonomous harmonic oscillators and yield accurate results for oscillatory problems at a low computational cost. Several numerical examples illustrate the performance of the new methods. Conclusions and pointers to further research are detailed in Chapter 6. / [ES] Esta tesis aborda el tratamiento de problemas perturbados con métodos de escisión (splitting). Tras motivar el origen de este tipo de problemas en el capítulo 1, introducimos los objetivos, varias técnicas básicas y métodos existentes en capítulo 2. En el capítulo 3 consideramos la integración numérica de ecuaciones no autónomas separables y parabólicas usando métodos de splitting de orden mayor que dos usando coeficientes complejos (métodos con coeficientes reales de orden mayor de dos necesariamente tienen coeficientes negativos). Proponemos una clase de métodos que permite evaluar todos los operadores con dependencia temporal en valores reales del tiempo lo cual genera esquemas estables y fáciles de implementar. Si el sistema se puede considerar como una perturbación de un problema resoluble de forma exacta y si el flujo de la parte dominante se avanza usando coeficientes reales, es posible construir métodos altamente eficientes para este tipo de problemas. Demostramos la eficiencia de estos métodos en varios ejemplos numéricos. En el capítulo 4 proponemos métodos de splitting para el cálculo de la exponencial de matrices perturbadas que se pueden escribir como suma A = D + epsilon*B de una matriz dispersa y eficientemente exponenciable con exponencial dispersa exp(D) y una matriz densa epsilon*B de noma pequeña. El algoritmo predominante se basa en escalar la matriz grande con un número pequeño 2^(-s) para poder exponenciar el resultado con métodos eficientes de Padé o Taylor y finalmente obtener la aproximación a la exponencial elevando al cuadrado repetidamente. En este contexto, el coste computacional proviene de las multiplicaciones de matrices densas y presentamos una cuadratura modificada aprovechando la estructura perturbada para reducir el número de productos. Resultados teóricos sobre errores locales y propagación de error para métodos de splitting son complementados con experimentos numéricos y muestran una clara mejora sobre métodos existentes a precisión media. En el capítulo 5, consideramos la integración numérica de la ecuación de Hill perturbada. Resonancias paramétricas pueden aparecer y esta propiedad es de gran interés en muchas aplicaciones físicas. Habitualmente, las ecuaciones de Hill provienen de una función hamiltoniana y la solución fundamental es una matriz simpléctica, una propiedad muy importante que preservar con los integradores numéricos. Presentamos nuevos integradores simplécticos exponenciales de orden seis y ocho tallados a la ecuación de Hills. Estos métodos se basan en una aproximación simpléctica eficiente a la exponencial de osciladores armónicos acoplados de dimensión alta y dan lugar a resultados precisos para problemas oscilatorios a un coste computacional bajo y varios ejemplos numéricos ilustran su rendimiento. Conclusiones e indicadores para futuros estudios se detallan en el capítulo 6. / [CA] La present tesi està enfocada al tractament de problemes perturbats utilitzant, entre altres, mètodes d'escisió (splitting). Comencem motivant l'oritge d'aquest tipus de problems al capítol 1, i a continuació introduïm el objectius, diferents tècniques bàsiques i alguns mètodes existents al capítol 2. Al capítol 3, consideram la integració numèrica d'equacions no autònomes separables i parabòliques utilitzant mètodes d'splitting d'ordre major que dos utilitzant coeficients complexos (mètodes amb coeficients reials d'ordre major que dos necesariament tenen coeficients negatius). Proposem una clase de mètodes que permeten evaluar tots els operadors amb dependència temporal explícita amb valors reials del temps. Esta forma de procedir genera esquemes estables i fàcils d'implementar. Si el sistema es pot considerar com una perturbació d'un problema exactament resoluble, i la part dominant s'avança utilitzant coeficients reials, es posible construir mètodes altament eficients per aquest tipus de problemes Demostrem la eficiència d'estos mètodes per a diferents exemples numèrics. Al capítol 4, proposem mètodes d'splitting per al càcul de la exponencial de matrius pertorbades que es poden escriure com suma A = D + epsilon*B (una matriu que es pot exponenciar fàcilment i eficientemente, com es el cas d'algunes matrius disperses exp(D), i una matriu densa epsilon*B de norma menuda). L'algorisme predominant es basa en escalar la matriu gran amb un nombre menut 2^(-s) per a poder exponenciar el resultat amb mètodes eficients de Padé o Taylor i finalment obtindre la aproximació a la exponencial elevant al quadrat repetidament. En este context, el cost computacional prové de les multiplicacions de matrius denses i presentem una quadratura modificada aprofitant la estructura de matriu pertorbada per reduir el nombre de productes. Resultats teòrics sobre errors locals i propagació d'error per a mètodes d'splitting son analitzats i corroborats amb experiments numèrics, mostrant una clara millora respecte a mètodes existens quan es busca una precisió moderada. Al capítol 5, considerem la integració numèrica de l'ecuació de Hill pertorbada. En este tipus d'equacions poden apareixer resonàncies paramètriques i esta propietat es de gran interés en moltes aplicacions físiques. Habitualment, les equacions de Hill provenen d'una función hamiltoniana i la solució fonamental es una matriu simplèctica, siguent esta una propietat molt important a preservar pels integradors numèrics. Presentams nous integradors simplèctics exponencials d'orden sis i huit construits especialmente per resoldre l'ecuació de Hill. Estos mètodes es basen en una aproxmiació simplèctica eficient a la exponencial d'osciladors harmònics acoplats de dimensió alta i donen lloc a resultats precisos per a problemas oscilatoris a un cost computacional baix. La eficiencia dels mètodes s'il.lustra en diferents exemples numèrics. Conclusions i indicadors per a futurs estudis es detallen al capítol 6. / Seydaoglu, M. (2016). Splitting methods for autonomous and non-autonomous perturbed equations [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/71358