高活性载体Ziegler-Natta催化剂的研究

<正> 用反应法(MgCl_2/ROH/TiCl_4)合成MgCl_2载体Ziegler-Natta催化剂已被聚烯焊工业越来越广泛的接受。这不仅是因为这种催化剂体系具有高活性,用于α-烯烃聚合能得到高等规度的聚合物;而且比用研磨法制备催化剂易于控制操作条件,合成这种催化剂的关键步骤是醇溶解MgCl_2,再在低温下与TiCl_4反应。放出HCl和形成Ti(OR)Cl_3的同时,MgCl_2再次从溶液中沉淀出来而得到很好的载体。过去,曾从不同

THE STUDY OF SUPPORTED ZIEGLER-NATTA CATALYSTS FOR POLYPROPYLENE

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.