Lanthanide thiolate complexes:: Novel initiators for ring-opening polymerization of ε-caprolactone

The ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) using lanthanide thiolate complexes [(CH3C5H4)(2)Sm(mu-SPh)(THF)](2) (1) and Sm(SPh)(3)(HMPA)(3) (2) as initiators has been investigated for the first time. Both of 1 and 2 were found to be highly efficient initiators for the ROP of epsilon-CL. The poly(epsilon-caprolactone) (PCL) with molecular weight M-n up to 1.97 X 10(5) and relatively narrow molecular weight distributions (1.20 < M-w/M-n < 2.00) have been obtained in high yield in the temperature range of 35-65 degrees C. According to the polymer yield, 2 showed much higher activity than 1. However, the number-average molecular weight of PCL obtained with 2 was much lower than with 1. The possible polymerization mechanism of the epsilon-CL polymerization has been proposed based on the results of the end group analysis of the epsilon-CL oligomer.