Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 12, Issue 35, Pages 8969-8978Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200600660
Keywords
aluminum; chain transfer; lanthanides; polymerization; yttrium
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Aminopyridinato-ligand-stabilized organoyttrium cations are accessible in very good yield through alkane elimination from trialkyl yttrium complexes with sterically demanding aminopyridines, followed by abstraction of one of the two alkyl functions using ammonium borates. At 80 degrees C and in the presence of small amounts of aluminum alkyl compounds, very high ethylene polymerization activities are observed if very bulky aminopyridinato ligands are used. During these polymerizations a reversible polyethylene chain transfer is observed between the organoyttrium cations and aluminum alkyls. The chain-transfer catalyst system described here is able to produce relatively long-chain (up to 4000 gmol(-1)) Al-terminated polyethylene with a molecular-weight distribution < 1.1. In the synthesis of higher molecular PE a slight increase in polydispersity with increasing chain length (15600 gmol(-1), -1.4) is observed owing to reduced reversibility caused by higher viscosity and precipitation of polymer chains (temperature of 80-100 degrees C).
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