Lanthanide Thiolate Complexes: Novel Initiators for Ring‐opening Polymerization of ε‐Caprolactone

The ring‐opening polymerization (ROP) of ε ‐caprolactone ( ε ‐CL) using lanthanide thiolate complexes [(CH 3 C 5 H 4 ) 2 Sm(μ‐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 ε ‐CL. The poly( ε ‐caprolactone) (PCL) with molecular weight M n up to 1.97×10 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 °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 ε ‐CL polymerization has been proposed based on the results of the end group analysis of the ε ‐CL oligomer.