Polylactides (PLAs) are among the most important synthetic biodegradable polymers investigated for biomedical and pharmaceutical applications such as controlled drug delivery, resorbable sutures, medical implants, and scaffolds for tissue engineering. [1] On the basis of annually renewable resources such as corn and sugar beets, PLAs are also promising degradable substitutes for petrochemical-based polyolefins. [2] The physical, mechanical, and degradation properties of PLAs are intimately dependent on the chain stereochemistry. For instance, isotactic poly(l-LA) (LA ΒΌ lactide), a highly crystalline material with a T m % 170 8C, has excellent mechanical properties and degrades rather slowly, whereas atactic poly(d,l-LA) is amorphous and subject to a relatively fast degradation. Stereocontrol, therefore, is crucial in the synthesis of polylactides. Most catalysts, including stannous octoate, zinc lactate, and aluminum alkoxides, do not bias towards different enantiomers in the ring-opening polymerization of d,l-lactide, thereby furnishing PLAs with randomly distributed stereocenters. [3] Recently it was reported that a few single-site lactide-polymerization catalysts did show stereoselectivity. For example, [(bdi)ZnOiPr] (bdi ΒΌ bdiiminate) polymerized d,l-LA in such a way as to afford a heterotactic PLA, and chiral tris(pyrazolyl)borate magnesium complexes preferentially polymerized meso-LA in the presence of a mixture of meso-LA and d,l-LA (diastereoselectivity). [4] It has long been a challenge to prepare PLAs with long isotactic sequences out of d,l-LA through isospecific polymerization (Scheme 1), since these stereoblock copolylactides are expected to be hard and strong as highly crystalline poly-(l-LA)s but with varying degrees of crystallinity and degradation rates, depending on the average length of the isotactic blocks. So far, examples of isospecific lactide polymerization are limited to Schiff base aluminum alkoxide catalysts in CH 2 Cl 2 or in toluene, [5] in which the binaphthyl Schiff base ligands impose the best stereochemical as well as molecularweight control. However, the synthesis of the binaphthyl Schiff base ligand is time-consuming. Besides, solution polymerization with these catalysts is not a practically viable process. The following requirements must be satisfied for a catalyst to be industrially attractive: 1) The starting organic ligands should be commercially available and inexpensive.