Ethylene polymerization and copolymerization with polar monomers by a neutral nickel catalyst combined with co-catalyst of Ni(COD)2 or Al(i-Bu)3

A neutral nickel (II) catalyst D, {[O-(3-cyclohexyl)(5-Cl)C6H2-ortho-C(H)=N-2,6-C6H3(i-Pr)(2)]Ni(Ph3P)(Ph)} has been synthesized and characterized by H-1-NMR, FTIR and elemental analysis. The results indicate that Al(i-Bu)(3) is an effective cocatalyst for the neutral nickel catalyst. With bis(1,5-cyclooctadiene) nickel(0) [Ni(COD)(2)] or Al(i-Bu)(3) as a cocatalyst, the neutral nickel catalyst D is active for ethylene polymerisation and copolymerisation with polar monomers (tertbutyl 10-undecenoate(BU), methyl 10-undecenoate (MU), allyl alcohol (AA) and 4-penten-1-ol (PO)) under mild conditions. The resulting polymers were characterized by H-1-NMR, FTIR, DSC, and GPC. 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 polymerization parameters which affect both the catalytic activity and properties of the resulting polyethylene were investigated in detail. Under the conditions of 20 mu mol catalyst D and Ni(COD)(2)/D = 3 (molar ratio) in 30 mL toluene solution at 45 degrees C, 12 x 10(5) Pa ethylene for 20 min, the polymerization activity reaches as high as 7.29 x 10(5) gPE center dot(mol-Ni-h)(-1) and M-eta is 7.16 x 10(4) g center dot mol(-1). For ethylene copolymerization with polar monomers, the effect of comonomer concentrations was examined. As high as 0.97 mol% of MU, 1.06 mol% of BU, 1.04 mol% of AA and 1.37 mol% of PO were incorporated into the polymer, respectively, catalyzed by D/Al(i-Bu)(3) system.