Bismuth(III) Alkoxide Catalysts for Ring-Opening Polymerization of Lactides and ε-Caprolactone

Homoleptic bismuth alkoxide complexes, Bi(OR)3 [R = iPr (1), tBu (2), and CMe2iPr (3)], are used as catalysts in the ring-opening polymerization (ROP) of lactides. In contrast to 1, two bulkier bismuth alkoxides, 2 and 3, show high activity in the ROP of lactides in toluene at 75 degrees C. Notably, BiIII alkoxides 2 and 3 are more active in lactide ROP than SnII octoate activated with n-butanol under identical reaction conditions. Bismuth alkoxides 2 and 3 exhibit a living behavior in the ROP of lactides that is demonstrated both in homopolymerization and in a polymerization resumption experiment. Polymerization of rac-lactide using 2 and 3 yields polylactide with a slight heterotactic bias. In addition, 2 is an efficient initiator for the ROP of E-caprolactone in bulk at 120 degrees C. Variation of the monomer-to-catalyst ratio yielded poly(E-caprolactone) with Mns up to 120 000 g mol1 in corrected gel-permeation chromatography (GPC) data.