| Although commercial multi-site Ziegler-Natta catalyst has very high activities in ethylene and other olefin polymerization, single-site catalyst is gaining increasing interests duo to the well-defined active site and the advantage of control over polymer molecular weight and molecular weight distribution. However the process difficulty of polyolefin is arisen from the narrow molecular weight distribution, which leads to more and more researches focusing on the dinuclear catalyst to produce polyolefins with broad molecular weight distributions. 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 improved. The present research work was concluded as follows: (1) seven dinuclear metallocene catalysts C6H2[(CH2C5H4)2MCl2]2(Catl,M=Ti; Cat2,M=Zr),(C5H5TiCl2)2{[(RC5H3)CH2](p-C6H4)O(C6H4-p)[CH2(C5H3R)]}(Cat3,R=H; Cat4,R=Me),(RC5H4TiCl2)2{[(C5H4)CH2](p-C6H4)S(C6H4-/j)[CH2(C5H4)]}(Cat5,R=H; Cat6,R=Me),(C5H5ZrCl2)2{[(C5H4)CH2](p-C6H4)S(C6H4-p)[CH2(C5H4)]}(Cat7), and four non-metallocene catalysts {[3,5-di-tBu-2-(O)C6H2CHN(Ph)][(Ph)NC(Me)C(H)C(Me)O]} TiCl2(Cat8),{[3,5-di-tBu-2-(O)C6H2CHN(Ph)]2[OC(Me)C(H)(Me)CN(C6H4)-(C6H4)N=C (Me)C(H)C(Me)O]Ti2Cl4}(Cat9),{3,5-di-Br-2-(O)C6H2CHN[2(O)C6H4]}TiCl2(Cal0), {3,5-di-Br-2-(O)C6H2CHN[2(O)C6H4]}[TiCl(C5H5)] (Cat11) have been synthesized and characterized by 1H NMR and elemental analysis. (2) Ethylene polymerization has been conduct with nine catalysts (Catl-Cat9) in the presence of MAO, and the effects of conditions on the polymerization were studied in detail. (3) The relationship between the catalyst activity and the structure of metallocene or nonmetallocene catalysts were discussed. (4) The bulk polymerization of MMA (methyl methacrylate) with non-metallocene catalysts (Cat10, Cat11) was explored.The results show as follows.In the ethylene polymerization by binuclear ansa-metallocene Cat1 and Cat2/MAO, The binuclear zirconium catalysts are more active than the binuclear titanium catalysts. The difference may be attributed to the properties of the metal atoms. The MWD of produced polyethylene are bimodal indicating more than one active species duringpolymerization. The melting points higher than 130℃ and 13C-NMR spectrum indicated that polyethylene formed by Cat1 or Cat2 is highly linear and highly crystalline.In the ethylene polymerization by binuclear metallocene containning hetero-atom Cat3-Cat7/MAO, under the same condition, it was found that the catalytic activity of titanocene Cat3 is lower than that of titanocene Cat5, which might be related to the variation of hetero-atom(from oxygen atom to sulfur atom). The catalytic activity of methyl-substitude titanocene is higher than nonmethylsubstitude titanocene (Cat6>Cat5, Cat4>Cat3), it can explain that the methyl group may stabilize the activity center. On the other hand the MWD of obtained PE is in the same order (Cat6>Cat5, Cat4>Cat3). The catalytic activity of zironocene is much higher than that of titanocene, but the MWD is greatly narrower than titanocene, it could be attributed to the different behaviours of metal atom. The melting points higher than 130℃ indicate that polyethylene formed by Cat3-Cat7 is highly linear and highly crystalline. It is obvious that the introduction of the hetero-atom into bridge not only increases the length of bridge but also shows electron-donating effect on the metal centers, which increases electron density at the metal atom and lowered the stability of the η2-alkene-metal bond resulting in a more weakly coordinated monomer, facilitating insertion into the growing polymer chain.In the ethylene polymerization of heteroligated nonmetallocene of titanium Cat8 and Cat9/MAO, both of the two complexes show moderately activity about 105 gPE / (mol-Ti-h). The catalytic activity of binuclear complex Cat9 is higher than mononuclear complex Cat8, which might be related to the rigid bridge in Cat9 stabilizing the complex. Under the condition of [Cat] =0.4×10-4 mol.l-1, [MAO]/[Cat] =2000, T=25℃, t=0.5hr, P= 1bar, the molecular weight of PE produced by Cat8 reached 3.2×105 and the MWD was 2.95. The molecular weight of PE produced by Cat9 reached 4.6×105 and the MWD was 3.12. The melting points higher than 137℃ indicated polyethylene formed by Cat8 and Cat9 highly linear and highly crystalline.In the MMA polymerization by nonmetallocene titanium complexes Cat10 and Cat11/ A1(i-Bu)3, both complexes could catalyze MMA polymerization in 0-60 ℃. Under the same condition, the catalytic performance Cat11 is better than Cat10 due to the Cpring in Cat11. under the condition of [MMA]/[Cat]=2000, [Al]/[Cat]=20,T= 60℃, t=15hr, the molecular weight of PE produced by Cat10 reached 3.6×105 and the MWD was 2.14. And the molecular weight of PE produced by Cat11 reached 4.3×105 and the MWD was 2.44. FI-IR result shows that syndyotacticity ratio of PMMA produced by Cat10 and Cat11 are about 85% and 86% respectively. |
PDF Full Text Request