Study On Synthesis And Catalysis For Olefin Polymerization Of Supported Titanocene Catalysts

In recent years, the polyolefins become the most widely used and the largestdemanded polymer products in the synthetic resin field because of their uniqueadvantages. It is well known that the catalyst plays the key role in the rapiddevelopment of polyolefin industry. With the growing demand for high-performancepolyolefin products, more and more researchers have been developinghigh-performance catalysts for olefin polymerization. Nowadays, the significantbreakthroughs have been made in both heterogeneous catalytic systems andhomogeneous catalytic systems. Metallocene catalysts have been becoming excellentand homogeneous catalyst systems for olefin polymerization, due to their uniquecatalytic advantages such as high catalytic activity, good copolymerization, single activesite and the possibility of tailoring the polymer properties. However, the polyolefinsobtained with single-site metallocene catalysts have narrow molecular weightdistribution and therefore causes some difficulties in the industrial processing.Comparable to mononuclear catalysts, binuclear or multinuclear metallocene catalystshave been developed to produce polymers with broad, bimodal or multimodal molecularweight distributions, therefore improving processing properties of the obtainedpolyolefins. Moreover, researchers are trying to immobilize the soluble metallocenecompounds at the appropriate carrier to produce the supported metallocene catalysts,which take advantage of the characteristics of heterogeneous catalyst and homogeneouscatalyst in order to achieve the desired performance.In this dissertation, we have mainly done two aspects of the work as followed:(1) Three new triphenolate ligands have been synthesized, and were further used toimmobilize metallocene to produce the supported metallocene catalyst. Reaction of4,4′-biphenyl-(Me4CpTiCl3)2with different ligand lithium produced the multinuclearsupported titanocene catalysts (CPTi1–CPTi3) with three dimensional space. Thesupported titanocene catalysts are detailly characterized by the techniques of elemental analysis, NMR spectra,13C CP/MAS NMR, SEM and BET. Activated with Al(iBu)3andPh3CB(C6F5)4or MAO, these supported catalysts were used for the ethylenepolymerization and the ethylene/n-hexene copolymerization reactions. The obtainedpolyolefins are characterized by DSC, GPC and13C NMR. The results indicated thatthese supported titanocene catalysts exhibit reasonable catalytic activity for the ethylenepolymerization when activated with Al(iBu)3and Ph3CB(C6F5)4, and the polyethyleneshave broad molecular weight distribution. The polymerization time can last for twohours. It was shown that the catalytic activity increases with increasing Al/Ti moleratios with a maximum activity at Al/Ti=200. The influence of polymerizationtemperature on activity has been evaluated and maximum activity was obtained at60oC.(2) Two new cyclopentadienyl titanium aryloxide complexes such as the1-phenyl-2,3,4,5-Me4CpTi(O-2,6-iPr2-4-nBu-C6H2)Cl2complex (Ti1) and[4,4′-biphenyl-(2,3,4,5-Me4Cp)2][Ti(O-2,6-iPr2-4-nBu-C6H2)Cl2]2(Ti2) have beensynthesized and characterized by elemental analysis, NMR spectra, and single crystalX-ray diffraction analysis. Upon activation with Al(iBu)3and Ph3CB(C6F5)4, twotitanium aryloxide complexes were evaluated in the ethylene polymerization in toluene.The obtained polyethylenes are characterized by DSC and GPC. The results show thatcomplexes Ti1and Ti2both exhibit reasonable catalytic activity for the ethylenepolymerization. The polyethylenes have moderate molecular weight and meltingtemperature. Studies related to the influence of the [Al]/Ti molar ratio on the catalyticperformance have shown that two catalyst precursors presented highest activities atAl/Ti=200. The influence of polymerization temperature on activity has beenevaluated and the highest activity was obtained at60oC.