| Based on the ethyl-isobutylaluminoxane (EBAO), a series of novel aluminoxanes (modified EBAOs) were synthesized and their cocatalytic performances in the ethylene polymerization were studied.Three substituted boronic acids, i.e. phenylboronic acid, 4-fluorobenzeneboronic acid and n-butylboronic acid, were used to modify EBAO through the cohydrolysis of them and triethylaluminum (TEA) and triisobutylaluminum(TIBA) and water. The modified EBAOs, with different amounts of substituted boron, were marked as PB, FB and BB series respectively. With the reaction of one molar phenylboronic acid and two molar trialkylaluminum, TEA or TIBA, the phenylboronic acid modified tetraalkyl-aluminoxanes, PEAO and PBAO, were prepared respectively. The association of several aluminoxanes was measured by UV-visible spectroscopy. The results show that MAO, tetraethylaluminoxane (EAO21) and tetraisobutylaluminoxane (BAO21) were disassociated when their toluene solutions were diluted. Such variation was confirmed by the method of disassociation of aluminoxane with Lewis base, such as ether.The aluminoxanes mentioned above were used as cocatalysts in the ethylene polymerization catalyzed by Ni(II) complex {(ArN=C(Me)-C(Me)=NAr)NiBr2 (Ar=2,6-C6H3(i-Pr)2)} and Fe(II) complex {(ArN=C(Me)-C5H3N-C(Me)=NAr)FeCl2 (Ar=2,6-C6H3(i-Pr)2)}. The effect of the structure and the amount of aluminoxanes, polymerization temperature and ethylene pressure on the ethylene polymerization was mainly investigated. And the polymerization mechanisms of these two typical catalytic systems were also discussed.As for the Ni(II) catalytic system, the polymerization activity increased as the Al/Ni molar ratios increased or the polymerization temperature lowered, while the molecular weight and its distribution of the resulted polymer were hardly influenced by the changes of those polymerization conditions. The stronger Lewis acidity and the bulkier substitutes of aluminoxanes can result in the higher polymerization activities. For example, the activities of Ni(II)/FB series systems were higher than Ni(II)/EBAO system. But the structures of aluminoxanes do not affect the molecular weight and its distribution of PE obviously.The branching degree of PE prepared by Ni(II) complex increased with the incrementof polymerization temperature and the decrease of ethylene pressure. The resulted polymer was characterized with DSC, GPC and 13C NMR. Concerning with PE produced by Ni(II) complex at 30℃, the methyl branch (mainly including isolated methyl branch, and some other paired branches) was predominant with some short branches ( such as ethyl, propyl, butyl and amyl) and long branches (including isolated long branch and 1,4-paired branches). Among total branches, the percentage of 1,4-paired long branches is close to that of ethyl branch, while the percentage of the isolated long branch is close to that of 1,4-paired methyl branches or 1,6-paired methyl branches. However, the branching of PE prepared by Ni(II)/FB10 was different from other polymers produced by other catalytic systems. For the polyethylene made by that catalytic system, the percentages of 1,4-paired and 1,6-paired methyl branches were higher than other systems and the percentage of 1,4-paired methyl branches was higher than that of 1,6-paired methyl branches, which were quite opposite to other systems. There were several peaks on the DSC spectra of the polymers with different branching degrees. In addition, the branching of PE decreased as the polymerization time extended.As far as the Fe(II) catalytic system, the higher the Al/Fe molar ratios, the stronger Lewis acidities and the higher reactivates of carbon-aluminum bond in the cocatalysts resulted in the higher polymerization activities. For the modified EBAOs systems, it showed that the descending order of polymerization activity was FB, PB and BB. In this paper, the tetraalkylaluminoxanes were firstly used as cocatalysts in the ethylene polymerization catalyzed by the late transition metal complexes. It was found that tetraethylalumionxa...
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