Browsing by Author "Chen, Eugene, advisor"
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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 Open Access Catalytic biomass conversion and upgrading into platform chemicals and liquid fuels(Colorado State University. Libraries, 2014) Liu, Dajiang, author; James, Susan, advisor; Chen, Eugene, advisor; Williams, John, committee member; Marchese, Anthony, committee member; Fisk, Nick, committee memberThe development of novel, efficient catalytic processes for plant biomass conversion and upgrading into versatile platform chemicals as well as oxygenated biodiesel and premium hydrocarbon kerosene/jet fuels is described in this dissertation. The chief motivation of using annually renewable biomass as the source of chemical building blocks and transportation fuels is to reduce societal dependence on depleting fossil fuels. Towards this goal, 5-hydroxymethylfurfural (HMF), the dehydration product from C6 (poly)sugars, has been intensively investigated as it has been identified as a versatile C6 intermediate or platform for value-added chemicals and biofuels. This work has developed several highly efficient and cost-effective catalyst systems for C6 (poly)sugars conversion to HMF under mild conditions, including ubiquitous and inexpensive aluminum alkyl or alkoxy compounds, recyclable polymeric ionic liquid (PIL)-supported metal (Cr, Al) catalysts, and thiazolium chloride, a recyclable Vitamine B1 analog. An integrated, semi-continuous process for the HMF production from fructose has also been developed, affording the high-purity HMF as needle crystals. Towards HMF upgrading into higher-energy-density fuel intermediates, developing new strategies of C-C bond formation or chain extension is of particular interest. In this context, this study has discovered that N-heterocyclic carbenes (NHCs) are highly effective organic catalysts for HMF self-condensation to 5,5'-dihydroxymethylfuroin (DHMF), a new C12 biorefining building block. This new upgrading process has 100% atom economy, can be carried out under solvent-free conditions, and produces the C12 DHMF with quantitative selectivity and yield, the hallmarks of a "green" process. More significantly, the C12 DHMF has been transformed catalytically into oxygenated biodiesels, high-quality alkane jet fuels, and sustainable polymers, thereby establishing DHMF as a new C12 biomass platform chemical.Item Open Access Polymerization catalysis for the precision synthesis of chiral and sustainable polymers(Colorado State University. Libraries, 2011) Miyake, Garret M., author; Chen, Eugene, advisor; Bailey, Travis, committee member; Prieto, Amy, committee member; Strauss, Steven, committee member; Wang, David, committee memberPolymerization catalysis for the precision synthesis of chiral and sustainable polymers is described in this dissertation. The central theme of chiral polymers has revolved around the employment of newly synthesized enantiomeric zirconocenium ester enolate catalysts. These catalysts have been utilized in the asymmetric coordination polymerization of prochiral functionalized vinyl monomers towards optically-active, solution stable, one-handed helical polymers. These enantiomeric catalysts have also been used in the successful kinetic resolution polymerization of a racemic methacrylamide monomer. The stereospecific polymerization of chiral oxazolidinone functionalized alkenes has been performed, producing highly isotactic polymers that assume helical or random-coil secondary conformations, dictated by the proximity of the chiral oxazolidinone to the main-chain of the polymer. Investigating applications of helical polymers, two pseudo-enantiomeric helical poly(phenyl acetylene)s bearing chiral organocatalyst side-groups have been synthesized and the effects of the helix-sense and helicity on the enantioselectivity of these catalysts was subsequently examined. Towards sustainable polymers, renewable butyrolactone-based vinylidene monomers are of particular interest in exploring the prospects of substituting the petroleum-based methacrylate monomers for specialty chemicals production. The polymerization of such monomers by group III and IV transition metal catalysts has been investigated resulting in the synthesis of sustainable polymers with controlled molecular weights. These butyrolactone-based monomers have also been successfully polymerized in a rapid and living fashion, using ambiphilic silicon propagating species.