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@ARTICLE{Lhmann:817897,
      author       = {Lühmann, Nicole and Niu, Aizhen and Allgaier, J. and
                      Stellbrink, Jörg and Zorn, Reiner and Linnolahti, Mikko and
                      Willbold, Sabine and König, Bernd and Grillo, Isabelle and
                      Richter, Dieter and Fetters, Lewis J.},
      title        = {{T}he {I}nitiation {M}echanism of {B}utadiene
                      {P}olymerization in {A}liphatic {H}ydrocarbons: {A} {F}ull
                      {M}echanistic {A}pproach},
      journal      = {Macromolecules},
      volume       = {49},
      number       = {15},
      issn         = {1520-5835},
      address      = {Washington, DC},
      publisher    = {Soc.},
      reportid     = {FZJ-2016-04495},
      pages        = {5397 - 5406},
      year         = {2016},
      abstract     = {An in situ 1H NMR study has been carried out to examine the
                      anionic initiation mechanism of 1,3-butadiene and
                      tert-butyllithium (t-BuLi) using n-heptane as solvent.
                      Additionally, mixtures of model compounds have been
                      investigated ex situ to simulate very early stages of
                      polymerization. The analysis of the NMR spectra in
                      combination with density functional theory (DFT)
                      calculations proves the coexistence of cross-aggregates of
                      t-BuLi and initiated chains and their crucial role for the
                      initiation mechanism. From the low concentrations of these
                      species showing a characteristic maximum at t ≈ 50 min and
                      the increase of the overall initiation rate constant with
                      ongoing initiation, we propose a double-stage autocatalytic
                      mechanism for this process. We first assume a fairly small
                      reactivity of butadiene and t-BuLi, which exists under these
                      reaction conditions as a tetrameric aggregate. However,
                      after the reaction of the first t-BuLi unit with a monomer
                      molecule, the reactivity of the remaining three t-BuLi units
                      in the aggregate is increased considerably. The crucial
                      second step of the autocatalytic mechanism is based on the
                      unimer exchange between partially or fully initiated t-BuLi
                      aggregates and the residual unreacted t-BuLi tetramers. As a
                      result, the initiation rate constantly increases and leads
                      to a sigmoidal consumption of initiator molecules during the
                      polymerization. In addition, the time-dependent
                      cross-aggregate concentrations are used as a benchmark for a
                      full mechanistic approach compiling all literature
                      assumptions. Numerical modeling allows a semiquantitative
                      description of the data.},
      cin          = {ICS-1 / Neutronenstreuung ; JCNS-1 / ZEA-3 / ICS-6},
      ddc          = {540},
      cid          = {I:(DE-Juel1)ICS-1-20110106 / I:(DE-Juel1)JCNS-1-20110106 /
                      I:(DE-Juel1)ZEA-3-20090406 / I:(DE-Juel1)ICS-6-20110106},
      pnm          = {551 - Functional Macromolecules and Complexes (POF3-551) /
                      6G4 - Jülich Centre for Neutron Research (JCNS) (POF3-623)
                      / 6215 - Soft Matter, Health and Life Sciences (POF3-621)},
      pid          = {G:(DE-HGF)POF3-551 / G:(DE-HGF)POF3-6G4 /
                      G:(DE-HGF)POF3-6215},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000381320300011},
      doi          = {10.1021/acs.macromol.6b01115},
      url          = {https://juser.fz-juelich.de/record/817897},
}