An apparatus was set up for in situ UV- Vis determintion of ethylene polymerization under atmospheric pressure. In three different solvents, tetrahydrofuran(THF), chlorobenzene and dimethyl formamide (DMF), and using MAO as cocatalyst,α- diimine/nickel catalytic system was prepared for ethylene polymerization with the UV- Vis testing system. In THF, active peak at 545 nm and inactive peak at 660 nm were observed. In chlorobenzene, active peak at 520 nm, 570 nm, and inactive peak at 660 nm were also observed. The regularities of growth and disappearence of active peaks were investigated. The structure of active species and solvent effect were discussed.
