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Reversible Chain Transfer between Organoyttrium Cations and Aluminum: Synthesis of Aluminum‐Terminated Polyethylene with Extremely Narrow Molecular‐Weight Distribution
Author(s) -
Kretschmer Winfried P.,
Meetsma Auke,
Hessen Bart,
Schmalz Thomas,
Qayyum Sadaf,
Kempe Rhett
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200600660
Subject(s) - alkyl , chain transfer , polyethylene , polymer chemistry , chemistry , dispersity , polymerization , ethylene , molar mass distribution , polymer , yttrium , alkoxide , catalysis , organic chemistry , radical polymerization , oxide
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 °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 g mol −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 (15 600 g mol −1 , ∼1.4) is observed owing to reduced reversibility caused by higher viscosity and precipitation of polymer chains (temperature of 80–100 °C).