COPOLYMERIZATION OF ETHYLENE WITH 1-OLEFIN OVER SUPPORTED  ZIEGLER-NATTA AND METALLOCENE CATALYTIC SYSTEMS 

Czaja K., Białek M.

University of Opole, Institute of Chemistry

Linear low-density polyethylene (LLDPE) synthesized by copolymerization of ethylene with 1-olefins is an important class of polymers because of specific properties. It is known that catalytic systems influence the structure of the copolymer and its properties like molecular weight, microstructure, density, melting point, and crystallinity. It is also known that Ziegler-Natta catalysts produce polymers with a wide molecular weight distribution (MWD) and comonomer distribution (CCD) due to multiple active sites. In contrast, homogeneous metallocenes are known as single site catalysts, which can produce very uniform polymers with narrow MWD's and CCD's.

We investigated the copolymerization process of ethylene with 1-olefins from 1-pentene to 1-dodecene over vanadium (VOCl₃, VCl₄) and titanium (TiCl₄) based catalysts supported on a complex of magnesium chloride with tetrahydrofuran MgCl₂(THF)₂ and activated by Et₂AlCl [1-3]. It was shown that vanadium catalysts demonstrate high activity in the copolymerization process and produce copolymers with higher comonomer content than titanium one. Simultaneously, it was found that the above magnesium complex can be used as a support of metallocene catalysts for the polymerization of ethylene. Therefore, it was reasonable to investigate the catalytic properties of the MgCl₂(THF)₂ supported metallocene system into the ethylene copolymerization process with higher 1-olefins [4 ]. 

The subject of this work is the study of the ethylene copolymerization with 1-hexene over zirconocene catalyst, Cp₂ZrCl₂/methylaluminoxane (MAO), supported on MgCl₂(THF)₂. The effect of 1-hexene concentration in the feed on catalyst productivity and comonomer reactivity as well as copolymer microstructure and other properties will be presented and compared with those obtained earlier for titanium and vanadium catalysts supported on the same carrier. After that the effect of the magnesium support modification by the organoaluminium compound (MAO, Me₃Al and Et₂AlCl) on the activity and reactivity of the supported catalyst as well as the properties of the copolymers obtained will be discussed.

[1] M.Białek, K.Czaja: Polimery 2000; 45, 293 and 353

[2] M.Białek, K.Czaja:  Polymer, 2000; 41, 7899

[3] K.Czaja, M.Białek: Polymer, 2001, 42, 2289

[4] M.Białek, K.Czaja et al.: Polymer, in press