Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item Versatile Strategies for Multifunctional Polyolefins(2023) Fischbach, Danyon Miles; Sita, Lawrence R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polyolefins have quickly become one of the world’s most utilized products since their discovery in the 1950s. With 350 million tons produced each year, it is clear that the use of polyolefins is not subsiding in the near future. Instead, it is imperative to develop novel materials that are more efficient than their current counterparts. As the function of a plastic is derived from its properties, creating polyolefins with designable and targetable attributes is a major priority. The Sita group has played a huge role in the development of ‘precision’ polyolefins. The techniques employed allow for the scalable synthesis of a plethora of polyolefins. To do this, input variables such as the monomer, tacticity, molar mass, and molar mass distribution are controlled in an organized manner to affect output properties such as crystallinity, elasticity, and tensile strength. The ability to create diverse plastics is necessary for the functions asked of them, however, the missing element in almost all polyolefin synthesis is chemical functionality. The inert nature of polyolefins leads to limited reactivity, therefore, reducing possible chemical reactions, such as recycling. The goal of this work is to increase the scope of functional polyolefins so that new materials with improved properties can be produced. The first step in adding functionality is choosing the proper functional group. A drawback to many polyolefin functionalities currently under study is that they have a very limited scope. Functional groups are designed and used individually, requiring different compounds for each target functionality. To overcome this obstacle, aryl functional groups were targeted in this report. Phenyl functionalities are known for undergoing a range of chemical transformations leading to a wide variety of possible materials. Described in this report, aryl-functionalized polyolefins were synthesized using three different techniques. Each method has been shown to later undergo post-synthetic transformations to yield new functional groups that can either be used as contact points for macromolecular building blocks or as chromophores for optical observation. The single use or combination of these techniques has led to polyolefin-based materials that may in fact lower the barrier for the next-generation of functional polyolefins.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.