Saudi Cultural Missions Theses & Dissertations
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Item Restricted Development of Scalable and Sustainable Processes for Polymer Recycling, Upcycling, and Synthesis(The University of Alabama, 2024) Al Alshaikh, Ali; Bara, JasonThe circular economy is a concept often heard of in the context of the plastic waste crisis. Yet, chlorinated plastics, polyvinyl chloride (PVC) in specific, are often left out of the circularity conversation, despite PVC being the third most produced plastic worldwide. This dissertation discusses the challenges facing chlorinated plastics, but also the unique upcycling opportunities they provide. Inspired by the potential, this dissertation showcases new methods and processes contributing towards the circularity of PVC. Fractionation is a technique often used for lignin separation, but rarely used in plastics. Here, PVC is fractionated using solvent mixtures of incrementing PVC-dissolution performance. Using a weak solvent (acetone) - nonsolvent (methanol) mixture, low molecular weight PVC fraction can be obtained. These fractions show remarkable solubility in solvents previously unconsidered in PVC chemistry. This work illustrates this via homogenous catalytic hydrogenation of dehydrochlorinated PVC. Using this method to modify PVC yielded products with polyethylene-like characteristics, while maintaining PVC properties and solubility, a feat rarely achieved in PVC modification. The methods developed open the door for a wide range of PVC modification paths. This success inspired ways to enhance the yield of soluble low molecular weight chains from bulk PVC. Thus, a method for the depolymerization of PVC was developed. Ozonolysis, while an “ancient” process, was never deployed as an approach for PVC depolymerization, only as an analytical tool. In this work, a new safe and scalable procedure for the ozonolysis of PVC was developed, yielding PVC products that are around a third or fifth the molecular weight of the starting material. The products were readily soluble in weak PVC solvents like acetone, aspiring use in 3D printing and PVC chemistry. While these methods cover a diverse range of concepts, they mainly belong to a single side of the circular economy, the end-of-life management. This dissertation also touches on another side, production, albeit of a different class of monomer. Vinylimidazoles were long produced using hazardous, and in some cases expensive, techniques. The methods reported in this work were considerably “greener,” covering nine out of the 12 principles of green chemistry. In totality, this dissertation diversly approached the end-of-life management of one of the most popular polymers, PVC, and the green production of a class of monomers previously produced using dangerous techniques.16 0Item Restricted Synthesis of lactone-based conjugated polymers for recently emerging n-type organic thermoelectrics and electrochemical transistors(University of Oxford, 2024-02-07) Alsufyani, Maryam; McCulloch, IainConjugated polymers (CPs) have demonstrated remarkable potential as electroactive components for various electronic applications over the past decades. Electron-transporting (n-type) materials, in particular, have been recognized to be essential in recently emerging i) clean energy conversion applications for developing efficient thermoelectric generators and ii) in bioelectronics for metabolite sensing that rely on electron generation or for developing complementary circuits. However, current n-type materials have limited scope and poor performance when compared to their p-type counterparts. This work explores enhancing the performance of n-type materials for organic thermoelectrics (OTEs) and organic electrochemical transistors (OECTs), through strategic chemical design, and structure-property relationship elucidation. The polymer series designed in this work consists of electron deficient lactam and lactone building blocks, with a particular focus on the significance of the lactone unit on the polymer electron affinity (EA). The first two studies are dedicated to exploring and optimizing the thermoelectric performance of a series of six lactone-based n-type polymers. This was achieved through chemical design modulation of acene ring size, and side chain length/polarity, resulting in n-type polymers with a state-of-the-art thermoelectric performance. The third study investigates the implementation of the earlier developed polymers in OECTs, particularly, focusing on the role of superoxide formation from electron transfer during polaron transport. This study demonstrates that turning off the thermodynamic favorability of this reaction prevents superoxide formation, leading to more stable and higher performing devices. The work of this thesis will offer guidance to the field, by demonstrating the advantages that can arise from designing n-type semiconducting polymers with high electron affinity, in the fields of OTEs and OECTs.21 0