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Diffusion of Methylaluminoxane (MAO) in Toluene Probed by 1 H NMR Spin‐Lattice Relaxation Time
Author(s) -
Hansen Eddy W.,
Blom Richard,
Kvernberg Per Olav
Publication year - 2001
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/1521-3935(20011001)202:14<2880::aid-macp2880>3.0.co;2-x
Subject(s) - chemistry , activation energy , relaxation (psychology) , toluene , methylaluminoxane , diffusion , spin–lattice relaxation , atmospheric temperature range , rotational diffusion , lattice (music) , analytical chemistry (journal) , thermodynamics , nuclear magnetic resonance , molecule , polymer , organic chemistry , physics , polymerization , metallocene , psychology , social psychology , nuclear quadrupole resonance , acoustics
A critical evaluation of model‐fitted and observed 1 H NMR spin‐lattice relaxation time data ( T 1 ) of methylaluminoxane (MAO) dissolved in toluene suggests that the relaxation time of MAO is predominantly controlled by rotational motions. Within the Al concentration ( C Al ) range (10 –3 M < C Al < 1 M ) and the temperature range (90°C > T > 20°C) studied, the diffusion of MAO contributes with less than 20% (at the maximum concentration investigated) to the overall relaxation rate. For concentrations smaller than 0.5 M , the diffusion has no significant impact on the spin‐lattice relaxation time (< 5%). Nevertheless, the diffusion coefficient of MAO can be estimated from the rotational correlation time, as derived from a spin‐lattice relaxation time model discussed thoroughly in this work. This model gives information on the molecular dimension of MAO ((19.4 ± 0.4) Å), the activation energy of the diffusion process ((11.2 ± 0.7) kJ/mol), and the temperature/concentration dependence of the viscosity of the MAO solution.