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@ARTICLE{Stellbrink:58101,
      author       = {Stellbrink, J. and Niu, A. and Allgaier, J. and Richter, D.
                      and Koenig, B. W. and Hartmann, R. and Coates, G. W. and
                      Fetters, L. J.},
      title        = {{A}nalysis of {P}olymeric {M}ethylaluminoxane ({MAO}) via
                      {S}mall {A}ngle {N}eutron {S}cattering},
      journal      = {Macromolecules},
      volume       = {40},
      issn         = {0024-9297},
      address      = {Washington, DC},
      publisher    = {Soc.},
      reportid     = {PreJuSER-58101},
      pages        = {4972 - 4981},
      year         = {2007},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {Since its discovery as a crucial cocatalyst in metallocene
                      and post-metallocene olefin polymerizations
                      methylaluminoxane (MAO) has retained commercial and academic
                      status. In spite of continued interest the MAO structure
                      remains ambiguously defined. Because of limited alkane
                      solubility toluene emerged as the MAO solvent of necessity.
                      With time these toluene solutions can develop a gel
                      fraction. The MAO structures proposed include linear, ring,
                      ladder, and cyclic with the latter involving fused four and
                      six membered rings along with cage and drumlike
                      architectures. The linear and ring structures have aluminum
                      and oxygen valences of three and two respectively while the
                      other structures require Al/O co-ordination numbers of four
                      and three. MAO structural information has been gathered from
                      colligative property measurements, various NMR formats and
                      quantum chemical calculations. We have used small-angle
                      neutron scattering (SANS)fortified with static and dynamic
                      light scattering (SLS/DLS)as the primary analysis tool for
                      dilute MAO solutions (phi/phi* <= 0.6). The main structure
                      assayed is a linear polymer chain consisting of
                      [-Al(CH3)-O-] monomer units with an M-w of 20 kg/mol and a
                      negative second virial coefficient. The latter fortifies the
                      recognized state of play that toluene is a poor MAO solvent.
                      About 0.8 wt $\%$ of MAO was captured as large-scale
                      three-dimensional aggregates. Elemental analysis results
                      show that in these large-scale aggregates the ratio of O/Al
                      is significantly larger than for the smaller polymer chains.
                      Additionally the large-scale aggregates contain only a small
                      fraction of CH3 units. Those structures may be the precursor
                      aggregates to the previously observed macroscopic gel
                      fraction reported to form over time at room temperature. The
                      solutions studied in this work did not show gel formation
                      over an 8-month period at similar to 0 degrees C.},
      keywords     = {J (WoSType)},
      cin          = {IFF-5 / INB-2},
      ddc          = {540},
      cid          = {I:(DE-Juel1)VDB785 / I:(DE-Juel1)VDB805},
      pnm          = {Kondensierte Materie / Großgeräte für die Forschung mit
                      Photonen, Neutronen und Ionen (PNI)},
      pid          = {G:(DE-Juel1)FUEK414 / G:(DE-Juel1)FUEK415},
      shelfmark    = {Polymer Science},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000247678300035},
      doi          = {10.1021/ma062940v},
      url          = {https://juser.fz-juelich.de/record/58101},
}