Browsing by Author "Miyake, Garret, committee member"
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Item Embargo Advancements in the chemical recyclability of acrylic polymers through investigation of monomer design(Colorado State University. Libraries, 2024) Gilsdorf, Reid Anthony, author; Chen, Eugene, advisor; Miyake, Garret, committee member; Shores, Matthew, committee member; Herrera-Alonso, Margarita, committee memberDepolymerization is a key avenue of state-of-the-art recycling of polymeric materials. Although many polymers have been investigated for their ability to depolymerize, a subset of polymers has been widely left out of the conversation, polyolefins, or polymers containing C-C bonds in the polymer main-chain. Acrylic polymers are an important class of polyolefins used throughout the world in a variety of applications. One of the key drawbacks of the polymer, however, is their unfavorable depolymerization conditions, requiring high temperatures in expensive reactors. Although much work has been performed on the depolymerization of the most widely used acrylic polymer, poly(methyl methacrylate) (PMMA), there have been few reports on trying to improve upon the recycling methods, such as decreasing depolymerization temperature or gaining control over the depolymerization mechanism. In this work, key mechanistic steps of acrylic polymer depolymerization are investigated to gain fundamental understanding on the limitations faced during depolymerization and try to improve upon them. When poly(α-methylene-γ-butyrolactone) (PMBL) and poly(α-methylene-γ-methyl-γ-butyrolactone) (PMMBL) were investigated, the suppression of side reactions that occurred with PMMA depolymerization were identified, attributed to the pendant lactone tethering radical species together. Employing this tethering effect, the design of new polymers with pendant lactones and lower equilibrium polymerization temperatures (ceiling temperature or TC), was carried out, overall decreasing depolymerization temperatures and improving polymer recyclability. Finally, these new polymers were incorporated into the design of copolymers with PMMA and PMMBL in order to exploit the new polymers' depolymerizability without hindering thermomechanical properties. Overall, this work has shed light onto the importance of polyolefin design in, not just thermomechanical properties, but also polymerization and depolymerization behavior which will benefit the continued development of recyclable-by-design polymers.Item Embargo Advancing the utility of organic superbases in synthetic methodology(Colorado State University. Libraries, 2023) Sujansky, Stephen J., author; Bandar, Jeffrey, advisor; Miyake, Garret, committee member; Sambur, Justin, committee member; Cohen, Robert, committee memberDeprotonation is one of the most fundamental and important modes of molecular activation, making Brønsted bases a critical part of a synthetic chemist's toolbox. An exceptional class of Brønsted bases are organic superbases, which are finding increased use in modern synthetic methods due to their unique properties. This thesis describes the use of these unique properties to advance the synthetic utility of superbases in two ways; 1) improving superbase- catalyzed alkene hydrofunctionalization reactions; and 2) developing air-stable and convenient organic superbase prereagents. Chapter One describes organic superbases in detail to provide background and context for Chapters Two and Three. Within Chapter One, various classes of superbases are presented, as well as their unique properties, syntheses, and example applications. Finally, the limitations and challenges associated with the use of superbases are discussed. Chapter Two describes the Bandar Group's superbase-catalyzed alkene hydrofunctionalization methodology. Within this chapter mechanistic studies as well as computational modeling, done as part of a collaboration with the Paton Group, are presented. These mechanistic studies provided insight into the factors controlling the reaction equilibrium. This insight was then used to logically address the limitations associated with the original conditions reported by the Bandar Group in 2018. The results of this work help to improve reaction efficiency and to expanded substrate scope. This understanding also led to the development of a catalytic anti-Markovnikov aryl alkene hydration method that allows convenient access to β-aryl alcohols. Chapter Three describes the development of air-stable organic superbase precatalysts and prereagents. Superbase salts that decarboxylate were developed as a first strategy method to generate the neutral superbase in solution. This initial salt system then led to the discovery of stable superbase carboxylate salts that react with and open epoxide additives in situ to neutralize the superbase conjugate acid. This ring strain release strategy is shown to be effective at promoting a range of reactions including Michael-type addition, ester amidation, deoxyfluorination, SNAr and Pd-catalyzed cross coupling reactions. These superbase precatalysts and prereagents provide a means to access the unique properties of organic superbases from air-stable and easy-to-handle salts. Overall, Chapters Two and Three represent significant progress in advancing the utility of organic superbases in synthetic methodology. My work in Chapter Two, along with the Bandar's and Paton Group's efforts, meaningfully expanded the scope and usefulness of superbase- catalyzed alcohol addition reactions. Our new mechanistic understanding proved to be fundamental to a range of addition reactions and pushed the boundary of possible nucleophilic addition reactions. My efforts in Chapter Three, along with Garrett's significant contributions, have made organic superbase much more convenient to use, synthesize and store. This greater convenience and potentially lower cost can be expected to improve access to superbase chemistry and serve as the foundation for future discoveries. Additionally, the ability to control the concentration of superbase in solution will have many benefits in expanding substrate scopes and modulating reaction profiles where a strong base is required but is also detrimental to the overall process.Item Embargo Catalyzed chemical synthesis of designer poly(3-hydroxyalkanoate)s: tuning function, microstructure, and architecture of biodegradable polymers(Colorado State University. Libraries, 2022) Westlie, Andrea Hope, author; Chen, Eugene Y.-X., advisor; Miyake, Garret, committee member; Levinger, Nancy, committee member; Herrera-Alonso, Margarita, committee memberThis dissertation describes the development of a chemocatalytic route towards biodegradable poly(hydroxyalkanoate)s (PHAs) based on the ring-opening polymerization of eight-membered cyclic diolide, 8DL, by discrete yttrium complexes. This chemocatalytic platform has transformed the brittle, poly(3-hydroxybutyrate) (P3HB) to high performance, "designer" PHAs through the use of molecular catalysts and the development of a precision polymerization methodology. There continues to be a pressing need for biodegradable polymers in applications where material recovery is unlikely or impossible or where environmental leakage of the plastic waste is highly likely. PHAs are truly biodegradable polyesters that can degrade in ambient conditions such as aerobic soil and marine environments and these polyesters are laden with tunability enabled by their chirality, composition, and architecture. A major challenge in implementing PHAs is to achieve truly tunable thermomechanical properties for any application, coupled with desirable processing conditions at scale. A critical literature review overviews the decades-long history of various chemocatalytic routes towards PHAs with either controlled tacticity or composition. To demonstrate the scope of our chemocatalytic platform, extensive study of homo- and copolymerization of three 8DLR (R = Me, Et, Bu) has been performed. Judicious choice of catalyst to match the steric bulk of the monomer results in high activity and high stereoselectivity ROP of these uncommon PHA homopolymers and allows for highly precise random copolymers of rac-8DLMe with targeted compositions ranging from 5 ~ 40 % incorporation of 8DLR (R = Et, Bu). Moving from aliphatic to aromatic substituents allowed for the synthesis of unnatural and previously unknown PHA with a glass transition (Tg) above room temperature (RT). Aliphatic-aromatic copolymers with designed architecture as random or block copolymers could be synthesized as well. And finally, recently we have designed and synthesized discrete PHA triblock copolymers towards achieving thermoplastic elastomer materials. Overall, this work has used fundamental investigation into a stereoselective, coordination-insertion polymerization mechanism and the resulting structure-property relationships to design higher-performance PHAs that are, in some cases, competitive with commodity polyolefins. This work serves as a platform for further development of PHAs using this chemocatalytic route towards new topologies, compositions, and functions.Item Open Access The development of new synthetic methods and techniques using strong Brønsted bases(Colorado State University. Libraries, 2024) Hoteling, Garrett A., author; Bandar, Jeffrey, advisor; Miyake, Garret, committee member; Menoni, Carmen, committee member; Peebles, Christie, committee memberBrønsted bases are indispensable tools in synthetic chemistry and, as such, deprotonation serves as a ubiquitous mode of molecular activation. By pushing the boundaries of what is possible within the acid-base reaction paradigm, unique synthetic methods and techniques can be developed. The work described in this thesis focuses on gaining a fundamental understanding of strong-base chemistry in efforts towards the development of new base-promoted synthetic methods. Herein, Brønsted bases have been investigated in two ways; 1) the design and application of benchtop-stable precatalyst salts for valuable organic superbases; and 2) the implementation of base-promoted halogen-transfer to develop benzylic oxidative coupling reactions with alkyl (hetero)arenes. This dissertation consists of five chapters. Chapters One and Three provide background and motivation for the work disclosed in this dissertation. Chapters Two, Four and Five represent project areas I have developed with Chapter Two adapted from published work and Chapters Four and Five as drafts of unpublished work. Below is a list of the chapters including a summary of the content for each. Chapter One describes the importance of organic superbases and their relevance to the synthetic community and the Bandar Group as a whole. Presented here will be the various classes of superbases and their unique properties that distinguish them from other classes of bases. Additionally, applications and known limitations to use of these bases will be discussed here. Chapter Two describes work along with Dr. Stephen J. Sujansky on the development of benchtop-stable organic superbase salts and the method for their facile in situ activation. Here, air-sensitive organic superbases form salts when mixed with carboxylic acids that are indefinitely stable on the benchtop. When combined with an epoxide additive, the carboxylate will react to open the epoxide and generate an alkoxide that can neutralize the superbase conjugate acid. This strategy is effective at promoting catalytic Michael-type additions and polymerizations as well as stoichiometric substitution and Pd-catalyzed cross-coupling reactions. This strain-release mechanism not only provides an accessible precatalyst for air-sensitive superbases but provides a new opportunity for controlling base concentration in situ. Chapter Two describes the development of the Bandar Group’s base-promoted halogen transfer research program. The history and importance of this mechanistic platform will be discussed as well as previous reports in the area by our group. In this chapter, the mechanism of base-promoted halogen-transfer is described, which enables the exchange of weakly acidic C–H bonds for C–X bonds that can be subsequently substituted with a pronucleophile in situ. This section will also provide the necessary background and motivation for Chapters Four and Five. Chapter Four describes the development of a new method for the synthesis of benzylic amines from alkyl (hetero)arenes. The development, optimization, and scope investigation of this reaction are described herein. The results of this work represent the first general approach for benzylic C–H amination, functioning on a broad scope of alkyl (hetero)arenes and amine coupling partners. Chapter Five describes the use of base-promoted halogen-transfer to enable alkyl (hetero)arene desaturation. With ethyl- and longer alkyl-substituted arenes, after benzylic halogenation, elimination takes place in the presence of excess base, a process that is competitive iv with the substitution protocol described in Chapter Two. Here, this reactivity has been exploited to develop a general desaturation technique for alkyl (hetero)arenes. Under desaturation conditions, an amine pronucleophile can be added, at which point β-addition followed by subsequent desaturation affords the β -aryl enamine, which is a diversifiable functional handle. This chapter describes the development of desaturation, cascade enamine formation, and the modification of enamine products.