Although homogeneous metallocene catalysts show some specific characteristics, such as single site, extremely high catalytic activity, high ability to incorporate monomers, narrow molecular weight and comonomer distribution, and excellent control of stereoregularity, but they also suffer some drawbacks, a very large amount of MAO requirement, inability to be used in slurry or gas phase processes, and poor control of polymer morphology. Therefore, it is necessary to modify the catalysts for the… 相似文献
A FI (phenoxy-imine) Zr-based catalyst of bis[1-[(2,6-diisopropylphenyl)imino]methyl-3,6-ditertbutyl-2-naphtholato]zirconium(IV) dichloride was prepared by changing the ligand from salicylaldehyde imine ligand which is used for well known FI catalysts to 2-hydroxynaphthalene-1-carbaldehyde imine ligand and used for polymerization of ethylene. Replacement of the phenoxy-group by naphtholato-group does not provide any spatial difficulties in the ortho-position to oxygen, but introduction of the bulky alkyl substitution groups at the ortho position of the naphthoxy-oxygen and on phenyl ring on the N dramatically enhanced the activity of the catalyst, as well as viscosity average molecular weight (Mv) of the obtained polymer. The prepared catalyst could produce a high molecular weight polyethylene under the polymerization conditions used. The optimum activity of the catalyst was obtained at the reaction temperature of 40°C. Activity of the catalyst was continuously increased with increasing MAO concentration and monomer pressure and no optimum activity was observed in the range studied. Crystallinity and melting point of the obtained polymer were between 55–65% and 125–135°C, respectively. A molecular weight distribution of 1.55–2.75 was obtained under the polymerization condition used and the polydispersity was broadened with the time. The activity of the catalyst was not sensitive to the hydrogen concentration. However, higher amount of hydrogen could slightly increase the activity of the catalyst. 相似文献
This study investigated the effects of several organotin silica surface modifiers on the ethylene polymerization performance of (nBuCp)2ZrCl2‐based supported catalysts in which MAO and metallocene were sequentially loaded. Each organotin compound acted as a spacer, increasing the catalyst activity. However, the catalyst activity and of the resulting polyethylenes varied as follows: Activity and fractional Sn+ charge: nBuSn(OH)2Cl > MeSnCl3 > nBuSnCl3 > Reference catalyst; and, : Reference catalyst > nBuSnCl3 > MeSnCl3 > nBuSn(OH)2Cl. The above catalyst activity rating was explained considering the influence of the Lewis acidity, that is, the fractional Sn+ charge of the organotin modifiers on the generation, concentration, and electron density at the active [(nBuCp)2ZrMe]+ cation. All the catalysts showed fairly stable kinetic profiles and produced narrow molecular weight distribution resins; 2.8 ≤ PDI ≤ 3.
The present article reveals important roles of metal alkyl activators in tuning the performance of the Phillips catalyst in ethylene polymerization. The addition of aluminum alkyl aids the activation of the catalyst, while excess addition leads to the loss of the activity. The balance between the activation and deactivation depends on the type of employed aluminum alkyl, and tri‐n‐octylaluminum offers the most efficient catalyst usage by preferentially suppressing the deactivation. The passivation of aluminum trialkyl with a hindered phenol mildens not only the deactivation but also chain transfer reactions, leading to an increment of high molecular weight fractions.
In the current work, we will focus on the influence of support properties on the activity and molecular weights of polyethylene produced with a metallocene supported on silica treated with MAO. It is demonstrated that relatively small changes in the size of the silica particles have a profound effect on the activity of the growing particles, and that not all particles in a given batch of catalyst behave in the same manner. 相似文献
The complex [N‐(2,6‐diisopropylphenyl)‐2‐(2,6‐diisopropylphenylimino)‐propanamidato‐κ2N,O](η1‐benzyl)nickel(lutidine) is immobilized on an acid‐treated montmorillonite. When the montmorillonite is treated with alkylaluminum, the catalyst shows a high activity with high molecular‐weight polyethylene. The catalytic behavior of the polymerization suggests isomerization of the complex on acid sites of the support surface. 相似文献
A series of 2,6-bis（imino）pyridyl iron and cobalt complexes bearing p-substituent [2,6-（ArN=CMe）2C5H3N]- MCl2 （Ar=2,6-Me2C6H3, 2,4,6-Me3C6H2, 2,6-Me2-4-BrC6H2, 2,6-Me2-4-ClC6H2, 2,4-Me2-6-BrC6H2, 2,4-Me2-6- ClC6H2, while M=Fe, Co） have been synthesized and investigated as catalysts for ethylene polymerization in the presence of modified methylaluminoxane as a cocatalyst. The electron effect and positions of the substituent of pyridinebisimine ligands were observed to affect considerably catalyst activity and polymer property. 相似文献
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