Ring-opening polymerization of D. L-lactide (D.L-LA) have been successfully carried out by using rare earth isopropoxides as catalyst for the first time.The effects of different rare earth isopropoxides different solvents LA/Ln molar ratio time and polymerization temperature on the polymerization reaction were investigated. It was found that the catalytic activity of different rare earth isopropoxides is as follows: La> M>Nd>Dy>Y
and the optium conditions of the ring-opening polymerization of D. L--LA were:[LA]:1.95mol/l
[Ln(OiPr)3]:6.5×10-3mol/l
90℃
toluene. A kinetic study has shown that the polymerization is first order in both monomer and catalyst. The apparent activation energy of the polyme-rization of D.L-LA with La(OiPr)3 is 67.7KJ/mol.