Heterobimetallic Catalysts for Ethylene Homo- and Co-Polymerization

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dc.contributor.advisorDo, Loi H.
dc.contributor.committeeMemberDaugulis, Olafs
dc.contributor.committeeMemberGilbertson, Scott R.
dc.contributor.committeeMemberTeets, Thomas S.
dc.contributor.committeeMemberRobertson, Megan L.
dc.creatorCai, Zhongzheng 1990-
dc.date.accessioned2019-05-23T14:11:14Z
dc.date.createdAugust 2018
dc.date.issued2018-08
dc.date.submittedAugust 2018
dc.date.updated2019-05-23T14:11:15Z
dc.description.abstractPolyethylene (PE) is one of the most important plastics in the world. The incorporation of polar functional groups into PE, even in low concentrations, can dramatically improve its material properties. The discovery that late transition metal Ni and Pd complexes can promote the coordination-insertion copolymerization of ethylene and polar olefins was a major scientific breakthrough. Unfortunately, their catalytic activities are significantly reduced in the presence of polar monomers compared to in the presence of non-polar monomers. It is believed that the formation of metal-monomer chelated complexes prevents efficient copolymerization. As a new strategy to avoid coordination inhibition by polar monomers, we first designed a new class of mononuclear nickel complexes that have pedant polyethylene glycol (PEG) chains that can bind alkali metal ions. Solution titration studies by UV-vis absorption spectroscopy demonstrated that optimal metal binding is achieved by selecting the appropriate PEG chain length to match the size of the alkali ions. Upon the addition of the alkali salts, the resulting heterobimetallic nickel-alkali metal catalysts were found to be more active in ethylene polymerization, compared to their parent nickel catalysts. They also produced polymers with higher molecular weight and higher branching compared to in the absence of the alkali ions. To test our strategy on other molecular systems, we also designed cationic palladium phosphine-phosphonate complexes with secondary metal-binding PEG chains. Solution studies by 1H NMR spectroscopy showed that a 1:1 binding stoichiometry between Pd and alkali ions can be achieved. The structure of the palladium-sodium species was confirmed by X-ray crystallography. Our heterobimetallic complexes exhibit significant enhancement in catalytic activity and thermal stability compared to their parent monometallic catalysts. For the copolymerization of ethylene and acrylates, our heterobimetallic complexes also showed higher activity and produced copolymer with higher molecular weight. Mechanistic studies conducted by low-temperature NMR spectroscopy revealed that the addition of alkali ions can accelerate ethylene insertion by the palladium acrylate intermediate.
dc.description.departmentChemistry, Department of
dc.format.digitalOriginborn digital
dc.format.mimetypeapplication/pdf
dc.identifier.urihttps://hdl.handle.net/10657/3985
dc.language.isoeng
dc.rightsThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).
dc.subjectBridging Ligands
dc.subjectCatalyst Design
dc.subjectCopolymers
dc.subjectHomogeneous catalysis
dc.subjectPolymerization
dc.titleHeterobimetallic Catalysts for Ethylene Homo- and Co-Polymerization
dc.type.dcmiText
dc.type.genreThesis
local.embargo.lift2020-08-01
local.embargo.terms2020-08-01
thesis.degree.collegeCollege of Natural Sciences and Mathematics
thesis.degree.departmentChemistry, Department of
thesis.degree.disciplineChemistry
thesis.degree.grantorUniversity of Houston
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy

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