Donor Atom‐Stabilized Aluminum Alkyls as Cocatalysts for the Ziegler–Natta Polymerization of Propene

Abstract

A number of organoaluminum compounds, stabilized with intramolecular nitrogen-or oxygendonor functions, have been used as cocatalysts for the MgCl 2 /TiCl 4 -catalyzed homopolymerization of propene as well as for the copolymerization of ethene with propene. The polymerization behavior of these aluminum alkyls was examined at different Al/Ti ratios within the range of 2 to 50 and compared with the reference of triethylaluminum (TEA). Especially (2) show the highest activities at very low Al/Ti ratios in the homopolymerization of propene, whereas TEA is almost inactive. The species [8-(N,N-dimethylamino)naphthyl]dimethylaluminum (4) reaches the highest activity of all examined alkyls and is very close to the highest value obtained with TEA. Bulky iso-butyl groups at the aluminum center are responsible for the very poor performance of the nitrogen stabilized cocatalysts [8-(N,N-The properties of the polypropenes synthesized with the stabilized organoaluminum species are similar to those produced with TEA but with a distinctly higher molar mass. In the case of 1, it was possible to increase the molar mass by a factor of three. For the copolymerizations, the compounds [2-(N,N-diethylaminomethyl)phenyl]diethylaluminum (7) and (2-methoxybenzyl)diisobutylaluminum (8) were found to be most suitable, producing polymers with significantly higher activities than TEA. For all copolymers two fractions were obtained, one crystalline fraction with a low and an amorphous part with a high amount of comonomer. In both fractions, 7 and 8 provide a higher comonomer incorporation than TEA.

Monomeric Alkylaluminum Complexes (dpp-BIAN)AlR2 (R = Me, Et, iBu) Supported by the Rigid Chelating Radical-Anionic 1,2-Bis[(2,6-diisopropylphenyl)imino]acenaphthene Ligand (dpp-BIAN)

“…Besides alkyl lithium and Grignard compounds, aluminum alkyls are the most widely used alkylating reagents in organic synthesis . In the past decade the authors representing the Berlin group prepared a number of intramolecularly O- and N-donor-stabilized alkyl aluminum compounds which serve well as reagents for the transfer of alkyl groups to organic molecules 2 and as cocatalysts in the Ziegler−Natta olefin polymerization . In general, aluminum alkyls tend to form dimers.…”

Buffered Aluminum Chloride as a Highly Efficient Cocatalyst for Olefin Dimerization and Polymerization

“…[28] Single-component equivalents of the Lewis base interaction with aluminum in ionic liquids are intramolecular donor-stabilized aluminum cocatalysts. Several of such aluminum compounds stabilized by pending intramolecular nitrogen, [29] phosphorus, [30] oxygen, [31] or sulfur [32] groups have been described and used as cocatalysts. These intramolecular-stabilized aluminum compounds, however, often require large synthetic efforts and still contain reactive AlÀC bonds.…”