Polymerization of l‐Lactide Catalyzed by Metal Acetylacetonate Complexes

Ring‐opening polymerizations (ROPs) of l ‐lactide (LA) were performed at 120°C, 140°C, 150°C, and 180°C in bulk catalyzed by acetylacetonate (acac) complexes of manganese(II), nickel(II), copper(II), zirconium(IV), dibutyltin(IV), and vanadyl(V). These experiments revealed that only the acac complexes of Zr and Bu 2 Sn were reactive enough to enable quantitative polymerization within a few hours. Further ROPs with Bu 2 Sn(acac) 2 and Zr(acac) 4 showed that Bu 2 Sn(acac) 2 had a slightly lower reactivity than the Zr complex. The ROPs catalyzed with Zr(acac) 4 yielded number average molecular weights ( M n ) up to 70,000 g mol −1 . The matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectra indicated an exclusive formation of cycles in the mass range of up to m/z 13,000 for Zr(acac) 4 and up to m/z 18,000 for Bu 2 Sn(acac) 2 . Unusually high melting temperatures (187°C–192°C) were also achieved along with high crystallinities. Furthermore, four lactide/glycolide copolymerizations catalyzed by Zr(acac) 4 were performed, and the topology and the extent of transesterification were characterized by MALDI‐TOF mass spectrometry and 13 C NMR spectroscopy.