Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item DESIGN AND SYNTHESIS OF POLYOLEFIN MATERIALS FOR NANOSTRUCTURED SELF-ASSEMBLY: BUILDING BLOCKS, COPOLYMERS, AND POLYMER CONJUGATES(2022) Wentz, Charlotte Maria; Sita, Lawrence R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polyolefin based materials are essential to today’s society in both simplistic commodity plastics to complex nanostructured materials and optoelectronic devices. In order to better understand these materials and make new impactful innovations, there is a barrier of fabrication, scalability, versatility, and programmability. The answer to the world’s plastic waste problem lies not in removing our use of polymers but relies in better understanding their properties, utilizing them as building blocks in advanced materials, and creating a long-lasting advanced material. Towards the goal of overcoming limitations in fabrication and scalability the work herein presents on utilizing a toolbox of living polymerization techniques such as living chain transfer polymerization (LCCTP) where new functionalities, stereochemical microstructures, optical properties, and physical properties of the polyolefin can be designed and systematically controlled. The polyolefins made through these techniques are scalable and versatile with end-group functionalization creating a seemingly endless choice of polymer building blocks and polymer materials. In line with creating new technologies that are programable the polyolefin building blocks made herein are utilized in multiple conjugates to create and understand methods and mechanisms of solid-state nanostructured self-assembly and access rare nonclassical phases that are highly desirable for their properties and uses in a plethora of applications. The conjugates investigated involve either a sugar-based head group covalently bond to a polymer tail to access rare and misunderstood Frank Kasper phase order-order transitions, or a perylene chromophore core covalently bond on both sides of the core in a linear fashion to polymer domains to create highly florescent or optically active materials that are useful in organic technologies such as solar cells, light emitting diodes, or nanotechnology. These perylene based conjugates can self-assemble into unique columnar phases and single gyroid phase. These results with conjugates provide methods for reliable and programmable access to rich phase behavior through the design of the polyolefin domains.Item Development of Next Generation Living Coordinative Chain Transfer Polymerization and New Polyolefin Materials Obtained Therefrom(2021) Wallace, Mark Alexander; Sita, Lawrence R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The living polymerization of ethene, propene, higher carbon-number linear and branched chain α-olefins, and α,ω-nonconjugated dienes has provided the basis for the development of modern technological advances and achievements. The use of polyolefin materials is ubiquitous through the many plastic products produced on an over 300-million-metric-ton global scale annually. The sheer range and scope of these products is further underscored by the fact that such diversity is achieved from a very limited number of industrially relevant olefin monomer feedstocks. As such, continued advancement of polyolefin materials has been achieved through the design and validation of new polymerization methods and transition-metal catalysts that allow for the controlled production of polyolefins with tailored architectural features and physical properties. Furthermore, these methods and materials must generate the desired products in a fashion that is both cost effective and amenable to large scale production.Towards this goal, the work herein presents the design, validation, and implementation of ‘next generation’ living coordinative chain transfer polymerization (LCCTP) through five new polymerization methods for the synthesis of polyolefin materials with new functionalities, stereochemical configurations, optical activities, and with tailored molecular weight distribution profile and dispersity. These new methods include the design of a novel homochiral group 4 cyclopentadienyl, caproamidinate (CPAM) hafnium pre-initiator that exhibits unprecedented configurational stability. Most importantly, these new LCCTP methods allow for the generation of different classes of polyolefin materials in a controlled and scalable manner. Discussions concerning the design and application of these new methods, the materials they produce, and the future of these new advances will be presented.Item ELECTRONIC MODIFICATION WITHIN THE WELL-ESTABLISHED CPAM FRAMEWORK AS A MEANS TOWARD INCREASED REACTIVITY(2017) Thompson, Richard; Sita, Lawrence R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Early transition metals (group IV-VI) supported by the pentamethylcyclopentadienyl-amidinate mixed ligand set (CPAM) have been found to enable a number of important chemical transformations including (living) coordinative polymerization of alpha-olefins, fixation of dinitrogen and group transfer chemistry involving oxo, imido and sulfido ligands to unsaturated organic substrates, including carbon dioxide. A great deal of the allure and success associated with these complexes is their modularity, particularly as it concerns the amidinate component which is tunable at both the N-bound substituents as well as the distal position. Accordingly, a great deal of work has established that by reducing the sterics in all three positions engendered higher reactivity. There exists, however, a practical “steric wall” such that the size of substituents can only be contracted so much. Tuning of the electronic character of these well-established systems could prove to be a novel and potent method for affecting reactivity of these complexes within an already well understood steric environment.