The effect of electron donors in Ziegler-Natta catalysts supported on recrystallized MgC12

• Juan Chirinos Universidad del Zulia-Venezuela
• Minerva Hidalgo Universidad del Zulia-Venezuela
• Tamara Rajmankina Universidad del Zulia-Venezuela
• Alvaro Parada Universidad del Zulia-Venezuela

Palabras clave: polypropylene, Ziegler-Na ta catalyst, support, electron donors, polymerization

Resumen

The Ziegler-Natta catalysts based on TiCl4 supported on MgCl2 which was recristallized by evaporation, were prepared. Ethyl benzoate (EB) and dioctyl phtalate (DOP) were used as internal Lewis bases. In the reactions of propylene polymerization, AlEt3 was used as cocatalyst and DOP as an external base forming pair, internal/external base, with the catalysts that contained EB. The percentage of supported titanium determined colorimetrically was in the 7-15% range. depending on the type of base present and its concentration. In comparison with the reference catalysis, the base modified cataIysts showed better activities, as well as an increase in the isotactic index obtained by extraction with boiling n-hepthane; the highest values of the isotactic index were obtained in the cases where DOP was used as an external base, although the activity was notably reduced. The viscosimetrlc molecular weights for the polymers obtained with the modified catalysts were lower than those obtained for the unmodified catalysts. The morphology of the catalysts and polymers, studied by Scanning Electronic Microscope (S.E,M.), was affected by the presence of the bases; a reply effect was observed.