Bismuth-Triflate-Catalyzed Polymerizations of ε-Caprolactone

epsilon CL was polymerized using the triflates of lanthanum, samarium, magnesium, aluminum, scandium, and bismuth as catalysts. Bismuth triflate proved to be extraordinarily reactive, and catalyzed polymerizations of eCL even at 20 degrees C. Adding DTBMP reduced the polymerization rate only slightly. Furthermore, no evidence of a cationic mechanism was found by end-group analyses. Polymerization at 20 degrees C either in bulk or in solution only yielded polyesters of low or medium molecular weights ((M) over bar (n) up to 30 000 Da). Yet addition of alcohols allowed for a proper control of molecular weight and end-groups. Additionally, low catalyst concentrations and low temperature resulted in narrow molecular weight distributions and polylactones almost free of cyclic compounds.