Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 29: Polymerphysics I
CPP 29.6: Vortrag
Donnerstag, 28. Februar 2008, 11:00–11:15, C 130
MAO is a polymer! - Analysis of polymeric methylaluminoxane via small angle neutron scattering and neutron spin echo spectroscopy — Aizhen Niu1, •Jörg Stellbrink1, Jürgen Allgaier1, Dieter Richter1, Geoffrey W. Coates2, and Lewis J. Fetters2 — 1IFF, Forschungszentrum Jülich, D-52425 Jülich — 2Cornell University, Ithaca, New York 14853, USA
Since its discovery as a crucial co-catalyst in metallocene and post-metallocene olefin polymerizations methylaluminoxane (MAO) has retained commercial and academic status. In spite of continued interest the MAO structure remains until now ambiguously defined.
Here we present a combined SLS/DLS/SANS study on the structural properties of MAO in toluene solutions (φ/φ*≤0.6). In dilute solution the main structure assayed is a linear polymer chain consisting of [-Al(CH3)-O-] monomer units with a Mw of 20 kg/mol, Rg≈46Å and a negative second virial coefficient A2. The latter fortifies the recognized state of play that toluene is a poor MAO solvent. With increasing concentration SANS data reveal the (reversible) formation of interchain branching due to a change from 3 to 4 in the coordination number of the Al-atoms in the polymer backbone [1].
Moreover, preliminary analysis of neutron spin echo (NSE) experiments reveals a dynamical stiffness of MAO chains. Zimm dynamics typical for polymer solutions in a good solvents are crucially retarded indicating a large internal rotational barrier of MAO chains.
[1] J. Stellbrink et al., Macromolecules, 40, 4972, 2007.