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

Abstract

AbstractA number of organoaluminum compounds, stabilized with intramolecular nitrogen‐ or oxygen‐donor functions, have been used as cocatalysts for the MgCl2/TiCl4‐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 the alkyls [2‐(N,N‐dimethylaminomethyl)phenyl]dimethylaluminum (1) and [2‐(N,N‐dimethylaminomethyl)phenyl]diethylaluminum (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‐dimethylamino)naphthyl]diisobutylaluminum (5) and [2‐(N,N‐dimethylaminomethyl)phenyl]diisobutylaluminum (3). 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.