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SILYL KETENES AS BUILDING BLOCKS FOR SMALL MOLECULES AND POLYMERS

Xiang, Yuanhui
http://rave.ohiolink.edu/etdc/view?acc_num=case1561113802285453

Abstract Details

2019, Doctor of Philosophy, Case Western Reserve University, Chemistry.
Chemical composition dictates properties and applications of all organic compounds, from small molecules to polymers. In the field of synthetic organic chemistry, researchers have been inspired by Nature to prepare target small molecules with tailored chemical composition to access cytotoxic properties, for example. In the field of polymer chemistry, recent work has addressed the development of a new polymerization method to control the molecular weight and dispersity of the polymer, as well as defined sequence. However, much less energy and effort have focused on new polymer backbone development. Ketenes, of the general form RR’C=C=O, have been underestimated as building blocks for the preparation of tailored small molecules and polymers, mainly due to their propensity to undergo self-dimerization through C=C and C=O double bonds. However, the orthogonal reactivity of the C=C and C=O double bonds grants a fascinating potential to build molecules and materials. Indeed, the tendency of self-dimerization can be overcome through the use of silyl ketenes, stable due to hyperconjugation provided by the -silicon effect. Of particular interest is the use of silyl ketenes as monomers for chain growth polymerizations. Appropriate control of C=C/C=O polymerization can lead to three polymer backbone compositions: 1) propagation through C=C double bond generated a poly -diketone, these unique chemical structures may provide the material with the ability of heavy metal chelation, as well as enolization to yield rigid rod polyacetylene derivatives; 2) propagation through C=O double bond yields polyketeneacetal, a degradable polymer with alkene group amenable for modification; and 3) the alternating polymerization of C=C/C=O provides a polyester, another degradable polymer with alkene groups for further modification. Here I represent the use of silyl ketenes as building blocks for the preparation of novel small molecules and polymers. First, the reaction of triisopropylsilyl ketenes with nucleophiles are explored at a fundamental level for a better understanding of silyl ketene reactivity, then a multi-functional polymer backbone was synthesized through anionic polymerization. Attempts to control the chemical composition of the polymer by tuning the silyl group led to the discovery of a well-defined trimer generated from tert-butyldiphenylsilyl (TBDPS) ketene which can undergo thermal rearrangement to yield a highly functionalized 2-pyranone derivative. This result reveals the acidity of the -H of silyl ketenes and the preferred propagation through C=C bond. Then, the polymerization of TBDPS ketene initiated with thiolates was evaluated and observed to yield oligomers via polymerization of C=C; end group analysis demonstrates an attachment of benzyl thiolate and H on the polymer backbone and thus the formation of linear oligomers. Cyclic compounds were also isolated during this process, which can be attributed to intrachain backbiting, a side reaction that was prevented with higher monomer concentration, as well as using a bulkier initiator.
Emily Pentzer (Advisor)
335 p.
Chemistry; Organic Chemistry; Polymer Chemistry

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Citations

  • Xiang, Y. (2019). SILYL KETENES AS BUILDING BLOCKS FOR SMALL MOLECULES AND POLYMERS [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1561113802285453

    APA Style (7th edition)

  • Xiang, Yuanhui. SILYL KETENES AS BUILDING BLOCKS FOR SMALL MOLECULES AND POLYMERS. 2019. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1561113802285453.

    MLA Style (8th edition)

  • Xiang, Yuanhui. "SILYL KETENES AS BUILDING BLOCKS FOR SMALL MOLECULES AND POLYMERS." Doctoral dissertation, Case Western Reserve University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1561113802285453

    Chicago Manual of Style (17th edition)

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© 2019, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.