Abstract: The oligomerization of ethylene catalyzed by P-O ligands, diphenylphosphi nobenzoic acid(DPP)and diphenylphosphinoacetic sodium(DPE), has been investigated. In catalytic system DPP/NiCl₂·6H₂O/NaBH₄ the content of lower olefins(C₄⁼～C₈⁼)increases with increase of DPP/Ni molar ratio and the content of higher olefins decreases markedly. Phosphines P(CH₃)₂Ph, P(OPh)₃, P(C₄H₉)₃, PClPh₂ and PPh₃ added in the catalytic system DPE/NiCl₂·6H₂O/NaBH₄ increase the content of C₄⁼ up ot 77.96%～95 29% from 49.45%(without their addition). Among these phosphines only P(C₄H₉)₃ could increase the selectivity to linear α-olefin. The reaction conditions have been investigated.

Key words: ethylene, catalytic oligomerization, α-olefin, nickel chelate