THE STUDY OF SUPPORTED ZIEGLER-NATTA CATALYSTS FOR POLYPROPYLENE
高活性载体Ziegler-Natta催化剂的研究

The purpose of this paper is to study the synthesis chemistry of supported Ziegler-Natta catalysts for polypropylene. Four kinds of catalysts were made, the first one (catalyst-A) from MgCl2-A solution containing MgCl2, EH (2-ethylhexanol) and PA (phthalic anhydride) dissolved in decane; the second one (catalyst-B) from MgCl2-B solution containing MgCl2, EH and TBT (tetrabutoxy titanium); the third one (catalyst-C) from MgCl2-C solution containing MgCl2, EH, PA and TBT; the fourth one (catalyst-D) from MgCl2-D solution containing MgCl2 and EH. The activity of catalysts varied in the order; B>C>A>D. Both activity and stereospecificity of catalyst-D are very low. Catalyst-A and Catalyst-B have the same structures characterized by X-ray diffraction. A mechanistic scheme for the variety of reactions that occur during the preparation of the final catalyst is proposed by analysis of IR spectra. The catalyst-B has about 60% more activity and 2% less stereospeci -ficity as catalyst-A. The presence of BuO-group which has a less hindrance for monomer inserting has been identified as an improver of catalyst activity. The role of phthalic anhydride has been discussed in detail. Some "mono-esters" generated from the reaction between PA and ROH improved catalyst properties. When PA was added during the preparation of catalysts, the finished catalyst produces polypropylene not only in high activity, but also in much better stereospecificity.