A neutral nickel(Ⅱ)catalyst D,{[O-(3-cyclohexyl)(5-Cl)C_6H_2-ortho-C(H)=N-2,6-C_6H_3(i-Pr)_2]Ni(Ph_3P)(Ph)}hasbeen synthesized and characterized by IH-NMR,FTIR and elemental analysis.The results indicate that Al(i-Bu)_3 is aneffective cocatalyst for the neutral nickel catalyst.With bis(1,5-cyclooctadiene)nickel(0)[Ni(COD)_2]or Al(i-Bu)_3 as a co-catalyst,the neutral nickel catalyst D is active for ethylene polymerisation and copolymerisation with polar monomers(tert-butyl 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-NMR,FTIR,DSC,and GPC.From the comparative studies,Ni(COD)_2 ismore active than Al(i-Bu)_3 for ethylene homopolymerization,while Al(i-Bu)_3 is more effective than Ni(COD)_2 for ethylenecopolymerisation with polar monomers.The polymerization parameters which affect both the catalytic activity and propertiesof the resulting polyethylene were investigated in detail.Under the conditions of 20 μmol catalyst D and Ni(COD)_2/D=3(molar ratio) in 30 mL toluene solution at 45℃,12×105 Pa ethylene for 20 min,the polymerization activity reaches ashigh as 7.29×105 gPE.(mol.Ni.h)~(-1) and M_η,is 7.16×104 g.mol~(-1).For ethylene copolymerization with polar monomers,theeffect of comonomer concentrations was examined.As high as 0.97 mol% of MU,1.06 mol% of BU,1.04 mol% of AA and1.37 mol% of PO were incorporated into the polymer,respectively,catalyzed by D/Al(i-Bu)_3 system. A neutral nickel (Ⅱ) catalyst D, {[O- (3-cyclohexyl) (5-Cl) C_6H_2-ortho-C (H) = N-2,6-C_6H_3 (Ph)} has been synthesized and characterized by IH-NMR, FTIR and elemental analysis. The results indicate that Al (i-Bu) _3 is aneffective cocatalyst for the neutral nickel catalyst.With bis (1,5-cyclooctadiene) nickel ) [Ni (COD) _2] or Al (i-Bu) _3 as a co-catalyst, the neutral nickel catalyst D is active for ethylene polymerisation and copolymerisation with polar monomers (tert-butyl 10-undecenoate -undecenoate (MU), allyl alcohol (AA) and 4-penten-1-ol (PO)) under mild conditions. Studies on Ni (COD) _2 ismore active than Al (i-Bu) _3 for ethylene homopolymerization, while Al (i-Bu) _3 is more effective than Ni (COD) _2 for ethylenecopolymerisation with polar monomers. the catalytic activity and properties of the resulting polyethylene were investigated in detail The reaction of 20 μmol of catalyst D and Ni (COD) _2 / D = 3 (molar ratio) in 30 mL of toluene solution at 45 ° C. with 12 × 10 5 Pa of ethylene for 20 min, the polymerization activity reaches 29.2 × 105 gPE (mol.Ni.h) ~ (-1) and M_η, was 7.16 × 104 g · 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.