Pairs Of Methylene Aromatic Bridge Dinuclear Metallocene Compound Synthesis And Catalytic Polymerization Of Ethylene

Metallocene catalysts, with the possibility of tailoring the polymer properties such as the molecular weight and the molecular weight distribution as well as stereochemistry, have become the excellent catalysts for the polymerization after the Zieger-Natta catalyst. However, the molecular weight distributions of the polymers produced by metallocene catalysts are so narrow to cause some disadvantages on the process ability. In order to resolve those problems, some combined catalysts have been studied. On other hand, a variety of dinuclar metallocene compounds or multinuclear metallocenes, have been prepared to examine their catalytic properties. There are two mechanically linked metallocene units, since dinuclear complexes could be potentially useful as a new polymerization catalyst ascribed by the cooperative electronic and chemical interaction between two centers. It was found that the melting point, the crystal degree, the molecular weight and the molecular weight distribution of the polymer produced by dinuclear metallocene catalyst have been changed.Ten aromatophoredimethylene bridged dinuclear metallocene catalysts were synthesized in this work, including six phenylenedimethylene bridged dinuclear complexes, two 4,4'-biphenylenedimethylene bridged dinuclear complexes and two thiophenedimethylene bridged dinuclear complexes. They were all well characterized by element analysts, MS and ¹H NMR.Above the new dinuclear metallocene complexes were used as catalysts for ethylene polymerization in the presence of methylaluminoxane(MAO) respectively. The effects of experimental parameters on the polymerization, variation in the molar ratio of MAO/Cat., time , temperature and catalyst concentration, were studied in detail. The results show as follows.1. Every catalytic system can catalyze the polymerization of ethylene efficiently. The catalytic performances can be affected at a certain extent by varying polymerization conditions.In the polymerizations of Cat.1, Cat.3 and Cat.3/MAO, the catalytic activities of these catalysts and the molecular weights of the polymers reached 3.776×10⁵gPE.mol^-1.Cat^-1.hr^-1, 5.626 ×10⁵: 4.464×10⁵gPE.mol^-1.Cat^-1.hr^-1, 6.904×10⁵;4.128×10⁵gPE.mol^-1.Cat^-1.hr^-1, 7.018× 10⁵ respectively.In the polymerizations of Cat.4, Cat.5 and Cat.6/MAO, the catalytic activities of these catalysts and the molecular weights of the polymers reached 4.128 × 10⁵gPE.mol^-1.Cat^-1.hr^-1, 3.659X105;8.178X105gPE.mol"1.Cat"1.hr"1, 3.423X105;3.636X10s^E.mol"1.Cat"1.hr'1, 4.112X105 respectively.In the polymerizations of Cat.7 and Cat.8/MAO, the catalytic activities of these catalysts and the molecular weights of the polymers reached 4.346 X 105gPE.mol"1.Caf'.hr'1, 2.166X 105;9.609 X 105gPE.nK)Yl.Ca.t¹.ia'1, 3.257 X105 respectively.In the polymerizations of Cat.9 and Cat.lO/MAO, the catalytic activities of these catalysts and the molecular weights of the polymers reached9.917X 105gPE.mor1.Caf1.hr"1, 6.429 X105;14.154 X lOsgPE.ttsA^l.Czil.hi1, 1.203 X106 respectively.2. Although exiting isomer in the phenylenedimethylene bridged homobinuclear titanocene complexes, the activities of them do not show remarkable difference.3. The molecular weight distributions of polymers produced by the dinuclear metallocene catalysts(3.18-6.23) are much broader than that obtained by using single nuclear metallocene catalyst(Cp2TiCl2,2.15;Cp2ZrCl2,2.02) and show only a single peak. More than one kind of active species exists in the dinuclear catalytic system due to the cooperative electronic and chemical interaction. Each of active species contributes to a narrow distribution and the distribution peaks overlap at a certain extent, so the molecular weight distributions of polyethylene produced by the dinuclear metallocene catalyst are broader .4. The binuclear zirconium catalysts are more active than the binuclear titanium catalysts. The difference may be attributed to the properties of them.5. The thiophenedimethylene and biphenylenedimethylene bridged binuclear metallocene catalysts are more active than the phenylenedimethylene bridged dinuclear metallocene catalysts, In general, the activity increases with increasing of electron density at the metal atom, because increasing of electron density lowers the stability of the r\ -alkene-metal bond resulting in a more weakly coordinated monomer, facilitating insertion into the growing polymer chain. Alternatively, or, in addition, a higher electron density at the metal atom may weaken the metal-carbon o-bond of the growing polymer chain, which could also facilitate insertion of the monomer and hence lead to an increased rate of polymerization. In the thiophenedimethylene bridged binuclear metallocene catalysts, hyperconjugative effect of thiophene ring is better than that of phenylene, so they are more active than the phenylenedimethyl bridged dinuclear metallocene catalysts. S. K. Noh et al reported that binuclear catalysts with more [CH2] units in the spacing group representhigher activities. In other words, a longer bridging distance helps to increase the catalytic activity.6. The melting points of polyethylene produced by aromatophoredimethylene bridged dinuclear metallocenes are 129¹34°C, which means that the polymers are highly linear and highly crystalline.