Browsing by Author "Miyake, Garret, advisor"
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Item Open Access Advancements in organocatalyzed atom transfer radical polymerization by investigation of key mechanistic steps(Colorado State University. Libraries, 2022) Corbin, Daniel Andreas, author; Miyake, Garret, advisor; Finke, Richard, committee member; Rappé, Anthony, committee member; Kipper, Matt, committee memberOrganocatalyzed atom transfer radical polymerization (O-ATRP) is a controlled radical polymerization method employing organic photoredox catalysts to mediate the synthesis of well-defined polymers. The success of this method derives from its reversible-deactivation mechanism, where polymers are activated by reduction of a chain-end C-Br bond to generate a reactive radical for chain growth, followed by deactivation of the polymer by reinstallation of the dormant bromide chain-end group. As a result, the polymer chain can be grown by reaction of the polymer radical with alkene-based monomers, but undesirable termination and side reactions can be suppressed by minimization of the radical concentration through deactivation. In this work, key mechanistic steps of O-ATRP are investigated to understand the fundamental limitations of this method and improve upon them. When N,N-diaryl dihydrophenazines were investigated, side reactions were identified in which alkyl radicals add to the phenazine core, leading to new core-substituted PC derivatives with non-equivalent catalytic properties. Employing these core-substituted PCs in O-ATRP showed these side reactions can be eliminated to improve polymerization control. In addition, the deactivation step of O-ATRP and related intermediates were studied, which revealed new side reactions that can limit polymerization efficiency as well as influences on the rate of deactivation. Finally, methods to exert control over the deactivation process were developed as a means of improving polymerization outcomes in challenging systems. For example, the intermediate responsible for deactivation was isolated and added to a polymerization to increase the rate of deactivation and limit side reactions in O-ATRP. Alternatively, a similar outcome could be achieved through in-situ electrolysis to increase the concentration of the desired intermediate during the polymerization. Ultimately, this work has yielded insight into important mechanistic processes in O-ATRP that will continue to benefit the development of this method.Item Open Access Design and application of strongly reducing photoredox catalysts for small molecule and macromolecular synthesis(Colorado State University. Libraries, 2019) Pearson, Ryan Michael, author; Miyake, Garret, advisor; McNally, Andy, committee member; Szamel, Grzegorz, committee member; Li, Yan Vivian, committee memberThe synthesis and application of new families of strongly reducing organic photoredox catalysts are described in this dissertation. These compounds provide a platform on which catalytically relevant properties including redox potentials and absorption profiles can be tuned, as well as predicted in silico. The critical photophysical and electrochemical characteristics have been established for both dihydrophenazine and phenoxazine catalysts which enable their ability to be used as green alternatives to commonly used transition metal photocatalysts. Specifically, phenoxazines have been utilized to mediate organocatalyzed atom transfer radical polymerization (O-ATRP) for the production of well-defined polymers using visible light. To this end, a catalyst system able to synthesize acrylic polymers with predictable molecular weights and dispersities less than 1.10 has been developed. In addition, dihydrophenazines were shown to mediate trifluoromethylation and atom transfer radical addition reactions, while phenoxazines were able to mediate C-N and C-S cross coupling reactions in the presence of a nickel co-catalyst.Item Open Access Development of N-aryl phenoxazines as strongly reducing organic photoredox catalysts(Colorado State University. Libraries, 2020) McCarthy, Blaine Gould, author; Miyake, Garret, advisor; Bandar, Jeffrey, committee member; Krummel, Amber, committee member; James, Susan, committee memberN-aryl phenoxazines were identified as a new family of organic photoredox catalysts capable of effecting single electron transfer reductions from the photoexcited state. A number of phenoxazines bearing different N-aryl and core substituents were synthesized, characterized, and employed as catalysts. Spectroscopic and electrochemical characterization of these phenoxazines was used to establish structure-property relationships for the design of visible-light absorbing, strongly reducing organic photoredox catalysts. The application of phenoxazines as catalysts for organocatalyzed atom transfer radical polymerization (O-ATRP), a light-driven method for the synthesis of well-defined polymers, revealed the importance of several catalyst properties for achieving control over the polymerization. Investigation of the properties and catalytic performance of N-aryl phenoxazines has provided fundamental insight into the reactivity of organic excited state reductants and photophysical properties of organic molecules. The catalysts developed through this work provide sustainable alternatives to more commonly used precious-metal containing photoredox catalysts.Item Open Access Fundamental and applied studies of polymeric photonic crystals: the role of polymer architecture and 3D printing(Colorado State University. Libraries, 2020) Boyle, Bret Michael, author; Miyake, Garret, advisor; McNally, Andrew, committee member; Menoni, Carmen, committee member; Prawel, David, committee memberBlock copolymers (BCP) provide a bottom-up, economical approach to synthesizing polymeric photonic crystals (PC) through the process of self-assembly. Photonic crystals (PC) are defined as periodic, dielectric nanostructures able to reflect certain wavelengths of light within a photonic band gap. The ability to directly tailor the synthesis, conformation, and self- assembly of a BCP to affect the properties of the resulting PC material creates a modular platform for PC materials design. Even though this platform exists for polymeric PC materials, the direct result of modulating the polymer architecture on the dynamics, self-assembly, and application of PC materials remains relatively unexplored. To help close this gap, this dissertation presents the polymer synthesis, characterization, and self-assembly of macromolecules within two unique classes of polymer architecture, dendritic block copolymers (DBCP) and bottlebrush block copolymers (BBCP). DBCPs were shown to possess many characteristics similar to those of bottlebrush polymers such as a rod-like conformation, a reduced capability for chain entanglement, and lower glassy moduli compared to non-rigid, linear polymers. Further, DBCPs possess high free energy parameters, as well as glass transition temperatures below melt extrusion 3D printing operating conditions, and were shown to self- assemble into PCs during the process of 3D printing. DBCP PCs represented the first example of 3D printing structural color. For BBCPs, the backbone composition's effect on the global BBCP conformation and in modulating self-assembly processes was examined. The backbone composition was shown to dramatically shift the wavelength of reflection of the PC material at similar molecular weights as well as improve the fidelity of the nanostructure morphology as the molecular weight increases from 50,000 g/mol to 2 million g/mol. The structure-property relationships illuminated herein have laid the groundwork for new research efforts into engineering BCPs for novel PC applications.Item Embargo Leveraging bio-based monomers, chemical recyclability, and sustainable polymerization techniques for sustainable polymer synthesis(Colorado State University. Libraries, 2024) Bernsten, Simone Noelle, author; Miyake, Garret, advisor; McNally, Andy, committee member; Reynolds, Melissa, committee member; Reisfeld, Brad, committee memberPolymeric materials have become vital to everyday life since their commercialization. Although polymers are integral to many industries and consumers, their synthesis and use brings with them a myriad of environmental concerns. Unsustainability can arise even before polymer synthesis in that many synthetic polymers are made from petroleum-derived monomers which are inherently nonrenewable. Next, many polymers are synthesized using one or more unsustainable components such as precious metals including iridium and ruthenium. Finally, at the end of a polymer's useful life, options for recycling are limited by the inability to make virgin-quality materials that can be used for the same application as the original polymer. The work described in this thesis aims to address each of these issues. The polymerizations of several bio-based monomers are described. The use of organic photoredox catalysis to enable polymerization represents sustainable synthesis of polymers. Polymers exhibiting chemical recyclability are also investigated, wherein end-of-life materials can be depolymerized and used to produce virgin- quality materials. Ultimately, this work represents a diverse array of methodologies for increasing the overall sustainability of polymeric materials.Item Open Access Mechanistically-guided advancement of photoinduced organocatalyzed atom transfer radical polymerization(Colorado State University. Libraries, 2020) Buss, Bonnie Leigh, author; Miyake, Garret, advisor; Bailey, Travis, committee member; Shi, Yian, committee member; Herrera-Alonso, Margarita, committee memberPhotoinduced organocatalyzed atom transfer radical polymerization (O-ATRP) is a promising polymerization methodology which leverages radical reactivity to afford macromolecular products with a high degree of control over polymer molecular weights and molecular weight distributions, paired with the added benefit of spatial and temporal control over polymerization. This process, a metal-free approach, relies on photoexcitation of an organic photoredox catalyst which stringently mediates the radical activation and deactivation steps of an oxidative quenching catalytic cycle. To successfully operate this cycle, and thus control the polymerization, the rate of deactivation must be faster than both the rates of radical activation and monomer propagation. Central to the initial development of O-ATRP has been the design and study of strongly reducing organic photocatalysts, particularly in the context of methacrylate monomer polymerizations. However, as a burgeoning methodology, the full scope of O-ATRP has not yet been established. In this dissertation, efforts in addressing three key challenges in O-ATRP, including reaction scalability, complex architecture synthesis, and polymerization of challenging monomers, through manipulation of features of the oxidative quenching mechanistic cycle is presented. To address these challenges diverse approaches were employed, including adaptation to continuous-flow reactors, implementation of multifunctional initiating systems, and rational design of a new family of organic photocatalysts, ultimately facilitating progression of O-ATRP to a scalable and efficient approach in the well-defined synthesis of industrially-relevant materials.Item Open Access N,N-Diaryl Dihydrophenazine photoredox catalysis for organocatalyzed atom transfer radical polymerization(Colorado State University. Libraries, 2019) Ryan, Matthew David, author; Miyake, Garret, advisor; Chen, Eugene, committee member; Kota, Arun, committee member; Snow, Christopher, committee memberThe synthesis, application, and mechanistic investigation of the 5,10-diaryldihydrophenazine catalyst family as applied to organocatalyzed atom transfer radical polymerization is presented in this dissertation. The N,N-Diaryl Dihydrophenazine catalyst family, which will be referred to in this dissertation as the phenazines, are an appealing class of molecules due to their strongly reducing excited states, accessed through modular syntheses enabling a wide range of photophysical and electrochemical properties. This class of molecules represented the first example of organic catalysts capable of operating a controlled, visible light driven, organocatalyzed atom transfer radical polymerization for the precision syntheses of (meth)acrylic polymers. Phenazine catalysts were shown to polymerize (meth)acrylic monomers to polymers of very low dispersities (< 1.10) in a process with quantitative initiator efficiency; both features crucial to produce precision polymeric materials poised for myriad applications. Supported by computational efforts, mechanistic understanding and structure-property-catalyst activity relationships were identified and harnessed to design optimal polymerization conditions, which have laid the groundwork for new research efforts into highly reducing, visible light absorbing, organic photocatalysts.Item Open Access Oxidative quenching organic photocatalyst design, synthesis and application in dual nickel/photoredox-catalysis(Colorado State University. Libraries, 2023) Chrisman, Cameron Hayes, author; Miyake, Garret, advisor; Paton, Robert, committee member; Zadrozny, Joseph, committee member; Kipper, Matthew, committee memberThe work described in this dissertation focuses on the development of a new class of organic photocatalysts and the application of oxidative quenching photocatalysts in dual nickel/photoredox-catalysis. The design of new organic photocatalysts is crucial for eliminating the need to use rare/expensive ruthenium and iridium that have dominated the field of photoredox catalysis. Additionally, the majority of the catalysts describe here-in operate through an oxidative quenching mechanism that remains underexplored in the field of dual nickel/photoredox catalysis. The first detailed mechanistic study on oxidative quenching in this field is reported and applied in a broad range of couplings.Item Open Access Sustainable polymer synthesis through the design of organic photoredox catalysts and development of poly(norbornane trithiolanes)(Colorado State University. Libraries, 2023) Price, Mariel Jene, author; Miyake, Garret, advisor; Paton, Robert, committee member; Zadrozny, Joseph, committee member; Herrera-Alonso, Margarita, committee memberThere are many avenues through which the sustainability synthesis, use, and disposal of polymeric materials can be approached. One of the two approaches explored in this work is the sustainable design and use of polymerization catalysts. Proper employment of catalysis can greatly decrease the energy input required to synthesize polymers and intentional design of those catalysts can enable their use in small quantities without compromising their effectiveness or the sustainability with which they are made and used. Herein, the development of a new class of metal-free photoredox catalysts (made from abundant elements) which can use visible wavelengths of light (a readily available, replenishable, and mild source of energy) to control the polymerization acrylate monomers is reported. Through this work we provide insight into how catalyst structure can be tuned to achieve desired properties and what properties might render certain catalysts more effective at lower loadings. The second approach explored herein towards improving the sustainability of polymer synthesis, use, and disposal is related to the recyclability of the polymeric materials. In addition to sustainable synthesis through catalysis, one way to improve the sustainability of polymeric materials is to increase their viable economic lifetime. Polymeric materials that are readily recyclable prevent the loss of materials through disposal. In the work reported herein methods for the synthesis and polymerization of sulfur-containing monomers to generate polymeric materials with intrinsic recyclability are investigated, approaches for efficient depolymerization of such polymers improved, and the scope of these materials expanded.Item Embargo The design and synthesis of super reducing organic photocatalysts through mechanistic understanding with application towards unactivated arene activation(Colorado State University. Libraries, 2024) Green, Alexander Richard, author; Miyake, Garret, advisor; Paton, Robert, committee member; Bailey, Travis, committee member; Reisfeld, Brad, committee memberThe work described in this dissertation focuses on the understanding of an organic photocatalyst system through a degradation and mechanistic study, leading to development of a new class of organic photocatalyst and improved application. The design of new organic photocatalysts is crucial for eliminating the need to use rare and expensive ruthenium and iridium that have dominated the field of photoredox catalysis for the past decade. Additionally, most of the catalysts describe here-in operate through a unique two electron, one proton activation mechanism to generate a closed shell species which enables direct quenching towards unactivated arenes such as benzene, without the use of a stoichiometric amount of reductant such as solvated electrons coming from pyrophoric metals. The progress described within this dissertation provides a deeper understanding of tunable organic reductants and their function.Item Open Access Towards elucidating photochemical reaction pathways in nickel catalyzed cross coupling and organocatalyzed Birch reduction(Colorado State University. Libraries, 2021) Kudisch, Max, author; Miyake, Garret, advisor; Finke, Richard, committee member; Chung, Jean, committee member; Reisfeld, Brad, committee memberCarbon-nitrogen (C─N) bond forming reactions to couple aryl halides with amines are essential for the discovery and production of medicinal compounds. The state-of-the-art method uses a precious metal palladium catalyst at high temperatures which poses sustainability concerns. Recently, a method was reported in which an iridium photocatalyst (PC) works in tandem with a nickel catalyst under blue light irradiation to achieve C─N bond formation at room temperature. Herein, it was discovered that the iridium PC could be omitted if 365 nm light is used, constituting a precious metal-free approach. This discovery suggests that a nickel-centered excited state can mediate C─N bond formation, raising the possibility of an energy transfer type pathway in dual catalytic systems. The nickel complexes formed were identified for the first time and mechanistic evidence was found that is consistent with energy transfer with both [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) and a phenoxazine PC. A series of [NiBr2(amine)n] complexes were isolated, characterized, and detected in C─N coupling reaction mixtures. A theoretical framework for predicting energy transfer rate constant ratios based on Förster theory and UV-visible spectroscopy was developed. The phenoxazine PC was both predicted and found to exhibit faster energy transfer and enhanced reaction performance when compared with [Ru(bpy)3]2+. In addition, a light-driven, organocatalyzed system for Birch reduction was developed. Historically, Birch reduction to reduce an arene to a 1,4-cyclohexadiene has been limited by the required use of alkali metals which are pyrophoric and can be explosive. Under violet light, a benzo[ghi]perylene imide PC was found to reduce challenging arenes such as benzene, constituting the first visible light driven approach capable of this reactivity. Mechanistic studies were performed that are consistent with a catalytic cycle involving addition of OH─ to the PC to form an adduct, [PC─OH]─. Photolysis of the adduct forms OH• and the PC radical anion which subsequently undergoes photoionization, ejecting a solvated electron that reduces the substrate.