The In-Situ Copolymerization Of Ethylene By Tandem Catalytic System Of Single Non-Metallocene Catalyst With Two Different Co-Catalysts

A novel tandem catalytic system was investigated in this thesis to prepare branched polyethylene using single catalyst precursor activated with different two co-catalysts.This thesis was composed of three parts: (1) the oligomerization of ethylene was investigated by theβ-diketonate complex with AlEt₂Cl, AlEt₃ and Al(i-Bu)₃ as co-catalyst respectively; (2) the copolymerization of ethylene andα-olefins was also studied byβ-diketonate complex with MAO, AlEt₃ and Al(i-Bu)₃ as co-catalyst respectively; (3) the in-situ copolymerization of ethylene was carried out by singleβ-diketonate zirconium complex with different two co-catalysts. The main conclusions are as follows.The oligomerization of ethylene byβ-diketonate complex with different co-catalysts was investigated. The results revealed that the co-catalyst and the structure ofβ-diketonate complex had important influence on the activity and the distribution of the oligomers. Analysis by GC/MS showed that the oligomers obtained byβ-diketonate zirconium complex/AlEt₂Cl were mainlyα-olefins, while the oligomers obtained byβ-diketonate titanium complex were mainly alkane. The copolymerization of ethylene andα-olefins was carried out byβ-diketonate complex with MAO, AlEt₃ and Al(i-Bu)₃ respectively. ¹³C-NMR spectrum revealed that the copolymer was branched polyethylene.The in-situ copolymerizatin of ethylene was investigated by theβ-diketonate zirconium complex as single catalyst precursor, AlEt₂Cl as co-catalyst for oligomerization and MAO, AlEt₃, Al(i-Bu)₃ as co-catalyst for copolymerization of ethylene respectively. ¹³C-NMR spectra revealed that the resultant copolymers were branched polyethylene, and the melting temperature and crystallinity of the copolymers obtained decreased becaused of the branched structure in the polyethylene chain. Therefore, the branched polyethylene can be obtained by the novel approach using singleβ-diketonate zirconium complex activated with different two co-catalysts. It was proved that such novel tandem catalysis can also produce the two active species of oligomerization and copolymerization, and then synthesize the branched polyethylene by the in-situ copolymerization.The performance ofβ-diketonate zirconium complex/AlEt₂Cl/MAO was evaluated with the change of the ratio of two co-catalysts, n(Al)/n(Zr), the concentration ofβ-diketonate zirconium complex, polymerization temperature. The optimum values in polymerization were n(Al)/n(Zr)=100, T=60oC. At the same time, the effect of polymerization conditions on the tandem catalysis ofβ-diketonate zirconium complex/AlEt₂Cl/AlEt₃ andβ-diketonate zirconium complex/AlEt₂Cl/ Al(i-Bu)₃ were also investigated respectively.