| Introducing suitable functional groups into polyolefins to improve their properties, therefore, to widen their applications, have attracted scientists for several decades. A few approaches have been invented, but the incorporation of functional groups into the polyolefin chains by catalytic copolymerization under mild conditions is the optimal choice. Apparently, the key is to develop new catalyst.Late transitional metal catalysts, especially Grubbs type neutral nickel catalysts, surged in the middle 1990s sparked huge interests from academia and industry because of their good functional group tolerance. But the neutral nickel catalysts reported by Grubbs group were too expensive to apply in commercial. Accordingly, we focus on studying new practical neutral nickel catalysts and their performance for ethylene homopolymerization and copolymerization with polar monomers to obtain functionalization polyethylenes.Three new neutral nickel catalysts of 4a{[O-(3-CycIohexyl)(5-CH3)C6H2-ortho-C(H)=N-2,6-C6H3Pr]2Ni(Ph3P)(Ph)}, 4b{[O-(3-Cyclohexyl)(5-Cl)C6H2-ortho-C(H)=N-2,6-C6H3(i-Pr)2] Ni(Ph3P)(Ph)}, and 4c{[O-(3- Cyclopentenyl)(5-CH3)C6H2-ortho-C(H)=N-2,6-C6H3Pr]2Ni(Ph3P) (Ph)}, as well as their ligands and intermediates, have been synthesized and characterized by 'HNMR, FUR and elemental analysis. The single crystal of complex 4a was obtained, and its composition and molecular coordination geometry were determined by single crystal X-Ray diffraction and data analysis. In addition, a typical Grubbs type neutral nickel 4d{tO-(5-NO2)C6H3-ortho-C(H)=N-2,6-C6H3(i-Pr)2]Ni(Ph3P)(Ph)} and the cocatalyst Ni(COD)2 were prepared.New facile and economic synthetic methods for ligand synthesis were proposed, o-cyclohexyl-p-methylphenol (la) (yielded:69.5%) and o-cyclohexyl-p-chlorophenol (Ib) (yielded:53.6%) were prepared by a single step of Friedel-Crafts alkylation of para-substituted ophenol with cyclohexyl chloride. o-Cyclopentenyl-p-methylphenol(lc) (yielded:54.0%) was prepared by alkylation of p-cresol and Clasion rearrangement. Thereby, three new ligands (3a, 3b and 3c) were prepared.It is found that both Al(i-Bu)3 and Al(Et)3 are effective cocatalyst for the neutral nickel catalyst. But they are different from traditional cocatalyst of Ni(COD)2. For the 4a~d/Al(i-Bu)3 system, there is an obvious induction period. From the comparative studies, Ni(COD)2 is more active than Al(i-Bu)3 for ethylene homopolymerization, while Al(i-Bu)3 is more effective than Ni(COD)2 for ethylene copolymerisation with polar monomers. The tendency of polymeric chain transfer to aluminium atom is serious, especially at high aluminium ratio, leading to a rapid decrease in polymer molecular weight.The activity for ethylene polymerization decreases in the order: 4d>4b>4a>4c. The activity of 4d is highest, but decreases sharply when polar species are added. 4a and 4b exhibit good tolerance toward polar groups. The tolerance of the neutral nickel catalyst toward polar substance decreases in the order: diethyl ether > tetrahydrofuran > ethyl acetate > water >ethanol. Among4a~d, 4b, bearing a bulky cyclohexyl 3-position of the salicyaldiminato ring and an electron-withdrawing chlorine atom at the 5-position, is the best one, which exhibits high activity both in ethylene homopolymerization and in copolymerization with polar monomers under mild conditions. Under the conditions of 20 u mol catalyst 4b and Ni(COD)2/4b =3(mol.r.) in 30ml toluene solution at 45癈, 12xl05Pa ethylene for 20 min, the polymerization activity reaches as high as 7.29x105gPE.(mol.Ni.hy' and M, is 7.16xl04g.rnor'.Increasing reaction temperature leads to molecular weight of resulting polymer decrease and branching extend increase. For 4a~d/Al(i-Bu)j system, the suitable temperature is 55~65癈, while for 4a~d/Ni(COD)2 system, the suitable temperature is 45-55 . Higher catalytic activity and molecular weight of polyethylene with lower branches and higher melting point at higher ethylene pressure are achieved.Seven oxygen containing and nitrogen c...
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