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- All Subjects: Polymer Chemistry
- Creators: Ackerman, Laura
Description
The development of sustainable catalysts that exhibit exceptional activity has become a major goal of organometallic chemists. Considering their low cost and environmentally benign nature, the use of base metals in catalysis has recently been explored. This dissertation is focused on the development of manganese catalysts for organic transformations and inorganic polymerizations. Previous advances in Mn-based hydrosilylation and hydroboration catalysis are reviewed in Chapter 1 and set the stage for the experimental work described herein.In Chapter 2, the electronic structure of [(2,6-iPr2PhBDI)Mn(μ-H)]2 is explored. This compound was evaluated by density functional theory calculations, SQUID magnetometry and EPR spectroscopy at low temperature. Single crystal X-ray diffraction data was collected for related compounds that feature bridging X-type ligands. The data revealed how bridging ligands impact the Mayer bond order between the two Mn atoms and explained why [(2,6-iPr2PhBDI)Mn(μ-H)]2 is an active catalyst for organic transformations.
Chapter 3 spotlights the first study to systematically demonstrate commercial aminosilane CVD precursor synthesis by way of SiH4 and amine dehydrocoupling using [(2,6-iPr2PhBDI)Mn(μ-H)]2. In addition, the study provided an efficient and halogen-free preparation of highly cross-linked polycarbosilazanes under ambient conditions. Furthermore, exceptionally pure perhydropolysilazane was directly prepared from ammonia and silane at room temperature through dehydrogenative coupling. These are also the first reported examples of Mn-catalyzed Si–N dehydrocoupling.
This research was then extended to the Mn-catalyzed dehydrogenative coupling of NH3 and diamines to organic silanes. Organic polysilazanes and polycarbosilazanes were synthesized and the structures were characterized by NMR, FT-IR, and MALDI-TOF spectroscopy. The thermal properties and coating applications of the products were evaluated by TGA, DSC, X-ray powder diffraction, SEM and EDX. A turnover frequency (TOF) experiment using 0.01 mol% of [(2,6-iPr2PhBDI)Mn(μ-H)]2 revealed a maximum TOF of 300 s-1, which is the highest activity ever reported for this transformation.
The last chapter highlights the first examples of nitrile dihydroboration mediated by a manganese catalyst. Using 0.5 mol% of [(2,6-iPr2PhBDI)Mn(μ-H)]2, 14 nitriles were reduced with HBPin at 80 ℃ to afford N,N-diborylamines after 24 h. A mechanism was proposed based on the isolation of [(2,6-iPr2PhBDI)Mn(NCHPh)]2 as an intermediate and further substantiated by DFT.
ContributorsNguyen, Thu Thao (Author) / Trovitch, Ryan (Thesis advisor) / Jones, Anne (Committee member) / Ackerman, Laura (Committee member) / Arizona State University (Publisher)
Created2022
Description
Delamination of solar module interfaces often occurs in field-tested solar modules after decades of service due to environmental stressors such as humidity. In the presence of water, the interfaces between the encapsulant and the cell, glass, and backsheet all experience losses of adhesion, exposing the module to accelerated degradation. Understanding the relation between interfacial adhesion and water content inside photovoltaic modules can help mitigate detrimental power losses. Water content measurements via water reflectometry detection combined with 180° peel tests were used to study adhesion of module materials exposed to damp heat and dry heat conditions. The effect of temperature, cumulative water dose, and water content on interfacial adhesion between ethylene vinyl acetate and (1) glass, (2) front of the cell, and (3) backsheet was studied. Temperature and time decreased adhesion at all these interfaces. Water content in the sample during the measurement showed significant decreases in adhesion for the Backsheet/Ethylene vinyl acetate interface. Water dose showed little effect for the Glass/ Ethylene vinyl acetate and Backsheet/ Ethylene vinyl acetate interfaces, but there was significant adhesion loss with water dose at the front cell busbar/encapsulant interface. Initial tensile test results to monitor the effects of the mechanical properties ethylene vinyl acetate and backsheet showed water content increasing the strength of ethylene vinyl acetate during plastic deformation but no change in the strength of the backsheet properties. This mechanical property change is likely inducing variation along the peel interface to possibly convolute the adhesion measurements conducted or to explain the variation seen for the water saturated and dried peel test sample types.
ContributorsTheut, Nicholas (Author) / Bertoni, Mariana (Thesis advisor) / Holman, Zachary (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2020