Abstract: A new rare earth catalyst system was found.It is composed of(β-CH₃-allyl)₂LnCl₅Mg·2TMED(Ln)-R₃Al(Al)(Ln=Nd、Ce and La,T的ED:N,N,N′,N′-tetramethyl-ethylendiamine;R=Me-,Et-,i-Bu- and Oct-)for stereocontrol of isoprene polymerization. The catalyst was capable of carying stereoregularity of polyisoprene(PIP)in the wider range by changing the polymerization temperature,polymerization time,Al/Ln molar ratio, and solvent and giving lower molectilar weight polymers. The contents of cis-1, 4-,trans-1,4-,and 3,4-unit in PIPs ranged from 19% to 79%,17% to 78% and 0 to 3.5%,respectively.

Key words: isoprene polymerization, π-allyl rare earth catalyst, stereocontrol