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Dual Polymerization Pathway for Polyolefin-Polar Block Copolymer Synthesis via MILRad: Mechanism and Scope

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    Article

    Dual Polymerization Pathway for Polyolefin-Polar Block Copolymer Synthesis via MILRad: Mechanism and Scope
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    • Huong Dau
      Huong Dau
      Department of Chemistry, Center of Excellence in Polymer Chemistry (CEPC), University of Houston, 3585 Cullen Boulevard, Houston, Texas 77004, United States
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    • Anthony Keyes
      Anthony Keyes
      Department of Chemistry, Center of Excellence in Polymer Chemistry (CEPC), University of Houston, 3585 Cullen Boulevard, Houston, Texas 77004, United States
      More by Anthony Keyes
    • Hatice E. Basbug Alhan
      Hatice E. Basbug Alhan
      Department of Chemistry, Center of Excellence in Polymer Chemistry (CEPC), University of Houston, 3585 Cullen Boulevard, Houston, Texas 77004, United States
      More by Hatice E. Basbug Alhan
    • Estela Ordonez
      Estela Ordonez
      Department of Chemistry, Center of Excellence in Polymer Chemistry (CEPC), University of Houston, 3585 Cullen Boulevard, Houston, Texas 77004, United States
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    • Enkhjargal Tsogtgerel
      Enkhjargal Tsogtgerel
      Department of Chemistry, Center of Excellence in Polymer Chemistry (CEPC), University of Houston, 3585 Cullen Boulevard, Houston, Texas 77004, United States
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    • Anthony P. Gies
      Anthony P. Gies
      The Dow Chemical Company, Lake Jackson, Texas 77566, United States
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      Orcidhttp://orcid.org/0000-0002-3558-593X
    • Evelyn Auyeung
      Evelyn Auyeung
      The Dow Chemical Company, Lake Jackson, Texas 77566, United States
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    • Zhe Zhou
      Zhe Zhou
      The Dow Chemical Company, Lake Jackson, Texas 77566, United States
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      Orcidhttp://orcid.org/0000-0003-0869-2112
    • Asim Maity
      Asim Maity
      Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
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      Orcidhttp://orcid.org/0000-0002-5923-8596
    • Anuvab Das
      Anuvab Das
      Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
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      Orcidhttp://orcid.org/0000-0002-9344-4414
    • David C. Powers
      David C. Powers
      Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
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    • Dain B. Beezer*
      Dain B. Beezer
      Department of Chemistry, Center of Excellence in Polymer Chemistry (CEPC), University of Houston, 3585 Cullen Boulevard, Houston, Texas 77004, United States
      *Email for D.B.B.: [email protected]
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    • Eva Harth*
      Eva Harth
      Department of Chemistry, Center of Excellence in Polymer Chemistry (CEPC), University of Houston, 3585 Cullen Boulevard, Houston, Texas 77004, United States
      *Email for E.H.: [email protected]
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      Orcidhttp://orcid.org/0000-0001-5553-0365
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    Journal of the American Chemical Society

    Cite this: J. Am. Chem. Soc. 2020, 142, 51, 21469–21483
    Click to copy citationCitation copied!
    https://doi.org/10.1021/jacs.0c10588
    Published December 8, 2020
    Copyright © 2020 American Chemical Society
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    Abstract

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    This work explores the mechanism whereby a cationic diimine Pd(II) complex combines coordination insertion and radical polymerization to form polyolefin–polar block copolymers. The initial requirement involves the insertion of a single acrylate monomer into the Pd(II)–polyolefin intermediates, which generate a stable polymeric chelate through a chain-walking mechanism. This thermodynamically stable chelate was also found to be photochemically inactive, and a unique mechanism was discovered which allows for radical polymerization. Rate-determining opening of the chelate by an ancillary ligand followed by additional chain walking allows the metal to migrate to the α-carbon of the acrylate moiety. Ultimately, the molecular parameters necessary for blue-light-triggered Pd–C bond homolysis from this α-carbon to form a carbon-centered macroradical species were established. This intermediate is understood to initiate free radical polymerization of acrylic monomers, thereby facilitating block copolymer synthesis from a single Pd(II) complex. Key intermediates were isolated and comprehensively characterized through exhaustive analytical methods which detail the mechanism while confirming the structural integrity of the polyolefin–polar blocks. Chain walking combined with blue-light irradiation functions as the mechanistic switch from coordination insertion to radical polymerization. On the basis of these discoveries, robust di- and triblock copolymer syntheses have been demonstrated with olefins (ethylene and 1-hexene) which produce amorphous or crystalline blocks and acrylics (methyl acrylate, ethyl acrylate, n-butyl acrylate, and methyl methacrylate) in broad molecular weight ranges and compositions, yielding AB diblocks and BAB triblocks.

    Copyright © 2020 American Chemical Society

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    Supporting Information

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    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.0c10588.

    • Experimental procedures, characterization of key intermediates, and additional spectroscopic data (PDF)

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    Cited By

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    This article is cited by 48 publications.

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    Cite this: J. Am. Chem. Soc. 2020, 142, 51, 21469–21483
    Click to copy citationCitation copied!
    https://doi.org/10.1021/jacs.0c10588
    Published December 8, 2020
    Copyright © 2020 American Chemical Society
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