Dual Polymerization Pathway for Polyolefin-Polar Block Copolymer Synthesis via MILRad: Mechanism and Scope. Academic Article uri icon

abstract

  • 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 -carbon of the acrylate moiety. Ultimately, the molecular parameters necessary for blue-light-triggered Pd-C bond homolysis from this -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.

published proceedings

  • J Am Chem Soc

author list (cited authors)

  • Dau, H., Keyes, A., Basbug Alhan, H. E., Ordonez, E., Tsogtgerel, E., Gies, A. P., ... Harth, E

publication date

  • January 1, 2020 11:11 AM