Catalytic behavior of silyl-amide complexes for lactide polymerization

A series of silyl-amide complexes (=M{N(SiMe3)2}2) were examined as the catalysts for the ring-opening polymerization (ROP) of L-lactide. The catalytic activity of the silyl-amide complexes for zinc was compared with that of the silyl-amide complexes of tin in order to clarify the structural effects on the catalytic behavior. In the tin complexes, the addition of 1-dodecanol made the polymerization rate of L-lactide faster and suppressed the initiation with the N(SiMe3)2 ligands. The 1H NMR analysis revealed that the rates of ligand exchange for the N(SiMe3)2 and 1-dodecanol are different between the zinc and tin complexes. Based on this finding, melt polymerizations of L-lactide was conducted with the zinc catalyst to synthesize high-molecular-weight poly(L-lactide). The M n of the obtained polymer was found to become higher than 60,000 Da, which is required for the industrial application of polylactide, in a short reaction time. Open image in new window