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The polymerization of dimethylaminoethyl methacrylate (DMAEMA) catalyzed by the 1-cyclopentylindenyl lanthanide (Ⅱ) complex (1-C5H9C9H6)2Yb (THF)2 was investigated.The results indicated that the complex (1-C5H9C9H6)2Yb (THF)2 as a single component catalyst showed high activity.The conversion of the polymerization and the molecular weight of the polymer were affected by temperature, time, amount of catalyst and solvent in the polymerization process.The catalytic activity of (1-C5H9C9H6)2Yb (THF)2 enhanced significantly when a small amount of polar solvent THF was added into the polymerization system in which toluene was selected as the solvent.The optimal temperature of polymerization was about 0 ℃.Other modified substituted indenyl lanthanide (Ⅱ) complexes also showed good catalytic activity.The order of catalytic activity of the complexes was as follows: (1-C5H9C9H6)2Sm(THF)≈(1-C2H5C9H6)2Sm(THF)2＞(1-C5H9C9H6)2Yb(THF)2＞(1-PhCH2C9H6)2Sm(THF)2.The steric regularity of poly (dimethylaminoethyl methacrylate) (PDMAEMA) was characterized by 1H NMR spectra.The polymerization provided syndiotacticity-rich PDMAEMA.The molecular weight and the molecular weight distribution of PDMAEMA were measured by gel permeation chromatography.