Browsing by Subject "Sustainable polymers"

Now showing 1 - 5 of 5
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    Modeling Homo- and Heterogeneous Catalysis with Applications Ranging from Hydrocarbon Activation to the Synthesis of Sustainable Polymers
    (2020-08) Mandal, Mukunda
    The diverse chemical properties of compounds containing metal atoms are inherently highly tunable. In terms of size, they may be small molecular complexes consisting of only 1 or 2 metal atoms or, at the other extreme of scale, they may be crystalline solids with clusters of metal ions periodically dispersed in the structure of a metal–organic framework (MOF). In both cases, relevant chemistries can be tailored to fit specific needs, especially with respect to catalytic reactivity. For a molecular catalyst, the combination of metal atom and its ancillary ligand can be chosen carefully to optimize selectivity and activity, while in three-dimensional MOFs, the metal clusters (called nodes) and connecting organic molecules (called linkers) can be ‘mixed and matched’ to best suit a particular application. Because of the inherent complexity of these systems, experimental characterization of structure/activity relations can often be challenging. Starting from a set of reactants, obtaining a mechanistic picture of the steps leading to the product formation is also demanding since isolation of an intermediate does not necessarily guarantee involvement of the species in the ‘productive’ pathway of the mechanism. Theory and computation can be immensely helpful in these instances to gain molecular-level understanding of the reaction mechanism(s). One can explore multiple pathways that yield the product and then evaluate the feasibility of each pathway by comparing computed energetics. Mechanistic knowledge can then be exploited to establish a structure/property relation, thereby fostering the design of subsequent generations of the catalytic species, ideally having improved performance, and helping to further refine the overall model. This dissertation demonstrates the use of computational methodologies, primarily quantum mechanical density functional theory, to explore the electronic structures of various metal-organic systems and the roles they play in carrying out targeted catalytic processes. In particular, computational modeling efforts are presented that illuminate (i) mechanisms of sustainable polymer production and principles for designing new catalysts (Chapter 2), (ii) site-selective C–H bond functionalization having relevance in drug discovery and chemical biology (Chapter 3) (iii) C–H activation reactions in light hydrocarbons using bio-mimetic copper-complexes having the potential to address challenges in fuel liquefaction (Chapter 4), and (iv) MOF-based single-site heterogeneous catalysts capable of oxidation reactions having industrial relevance (Chapter 5).
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    Renewable Monomers and Polymers from Biomass-derived Acids and Furans
    (2021-02) Xu, Shu
    Biomass-derived acids and furans are great building blocks of renewable plastics. This thesis focuses on the synthesis of novel biomass-based reactive monomers and polymers as well as the study of degradation of polymeric materials. Chapter 2 covers the synthesis of a reactive lactone monomer from levulinic acid. Polymerization of this lactone produced a semicrystalline polyketoester with high melting temperatures. The hydrolytic degradation of this polyketoester was also studied. Under aqueous basic conditions or Brønsted acidic conditions, different degradation products were observed. Chapter 3 details the Diels-Alder reaction between furans and itaconic anhydride. The highly efficient Diels-Alder reaction between furfuryl alcohol and itaconic anhydride into a single diastereomeric adduct. This adduct was demonstrated to be a good building block for production of several aromatic compounds that are potentially reactive monomers and a metathesis polymer. Chapter 4 describes the production of alpha-methyleneglutarimides as reactive monomers for radical polymerizations. The synthesis of this monomer started from an itaconic acid derivative. We reported the thermal properties of these polymers as well as the attempt to depolymerization through mere heat. Chapter 5 is about an ongoing project targeting dimethylnaphthalenes from biomass. Poly(ethylene naphthalate) (PEN) is a poly(ethylene terephthalate) (PET) substitute with better mechanical properties, and dimethylnaphthalene is a precursor for producing PEN. Our attempt towards the synthesis of dimethylnaphthalene from biomass-derived feedstock is discussed in this chapter.
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    Supporting Data for Ductile Gas Barrier Poly(ester-amide)s Derived from Glycolide
    (2022-06-21) Jang, Yoon-Jung; Sangroniz, Leire; Hillmyer, Marc; hillmyer@umn.edu; Hillmyer, Marc
    The development of promising sustainable gas barrier materials, such as polyglycolide, poly(L-lactide), and poly(ethylene 2,5-furandicarboxylate) is an important alternative strategy to traditional plastics used for packaging where low gas permeability is beneficial. However, high degrees of crystallinity in these materials can lead to undesirably low material toughness. We report poly(ester-amide)s derived from glycolide and diamines exhibiting both high toughness and desirable gas barrier properties. These sustainable poly(ester-amide)s were synthesized from glycolide-derived diamidodiols and diacids. To understand structure-property relationships of poly(ester-amide)s, polymers with different numbers of methylene groups were compared with respect to thermal, mechanical, and gas barrier properties. As the number of methylene groups between ester groups increased, the melting temperature decreased and oxygen permeability increased in the even numbered methylene group series. We also found that they are readily degradable under neutral, acidic, and basic hydrolytic conditions. These high performance poly(ester-amide)s are promising sustainable alternatives to conventional gas barrier materials.
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    Supporting data for Primary data for Poly(4-ketovalerolactone) from Levulinic acid, Synthesis and Hydrolytic Degradation
    (2020-06-10) Xu, Shu; Wang, Yuanxian; Hoye, Thomas R; hoye@umn.edu; Hoye, Thomas R
    These files contain primary data along with associated output from instrumentation supporting all results reported in Xu et. al. Primary data for Poly(4-ketovalerolactone) from Levulinic acid, Synthesis and Hydrolytic Degradation. In Xu et al. we found: We report here the synthesis of poly(4-ketovalerolactone) (PKVL) via ring-opening transesterification polymerization (ROTEP) of the monomer 4-ketovalerolactone (KVL, two steps from levulinic acid). The polymerization of KVL proceeds to high equilibrium monomer conversion (up to 96% in the melt) to give the semicrystalline polyketoester PKVL with low dispersity. PKVL displays glass transition temperatures of 7 °C and two melting temperatures at 132 and 148 °C. This polyester can be chemically recycled through hydrolytic degradation. Under aqueous neutral or acidic conditions, the dominating pathway for polyester hydrolysis is through backbiting from the chain end. Under basic conditions, mid-chain cleavage, accelerated by the ketone carbonyl group in the backbone, promotes the hydrolysis of nearby backbone ester bonds. The final hydrolysis product is 5-hydroxylevulinic acid, the ring opened hydrolysis product of KVL. PKVL was also observed to degrade under the action of a Brønsted acid to a bis-spirocyclic dilactone natural product altaicadispirolactone, which is a dimer of KVL. This constitutes a rare example of a one-step synthesis of a secondary metabolite in which a polymer was the starting material and the sole source of matter. Analogous ROTEP of the isomeric 4-membered lactone 4-acetyl--propiolactone (APL) was also explored, although this chemistry was not as well-behaved as the KVL to PKVL polymerization.
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    Synthetic Biology Approach to New Sustainable Materials
    (2018-03) McClintock, Maria
    Rapid industrialization and an abundance of cheap petroleum fueled the production and development of a great variety of synthetic polymers in the twentieth century. Over the past 60 years, these materials have become a part of the fabric of modern life. They are pervasive; from the polyurethanes in our cars and furniture, to the polypropylene in a state of the art medical implant, we rely on synthetic polymers every day of our lives, to accomplish tasks both trivial and critical. However, production of these chemicals from petroleum feedstocks is unsustainable and damaging to the environment. One potential option for more sustainable production is to use microbial fermentation to generate industrial chemicals. Microbial fermentation offers the opportunity to produce chemicals from biomass, making the compounds produced renewable feedstocks. Furthermore, the conditions used for, and byproducts produced from, microbial fermentation are benign. However, many microbial monomers face challenges in terms of economic viability and utility. With this in mind, my PhD research has focused on developing engineering systems for production of novel and viable monomers, as well as implementation of biological monomers for material applications. Using metabolic engineering, I have implemented the first heterologous pathway for production of dipicolinic acid, an aromatic di-acid that could be used as a biological replacement for isophthalic acid, a major component of the performance polymers Nomex® and polybenzimidazole, as well as a useful additive in many other polymers. By working with collaborators, I have used ancestral reconstruction to improve the production of anhydromevalonolactone, a monomer that can serve as a sustainable alternative to poly(acrylate). Finally, I have worked to establish a new platform for developing zwitterionic materials. In this project, we were able to engineer E. coli to produce N-acetyl-serine, a compound that can be dehydrated to form an acrylate monomer with a protected amine. I then polymerized this monomer with styrene and developed zwitterionic coatings that show improved resistance to cell adhesion. Overall, my work has contributed to the development of new metabolic pathways and material applications of biologically-derived monomers.