Rare earth metal initiated ring-opening polymerization of lactones

The progress in the synthesis of organolanthanide complexes supports the ex ploration of these compounds as initiators for ring-opening polymerization (ROP) of lactones. The performance of these initiators in terms of yield, m olecular weight, polydispersity, stereoregularity is affected by the ligand s and by the oxidation state of the respective rare earth metals. Several i nitiators are known to initiate living polymerization of lactones with exce llent polydispersities of the thus obtained polymers. Differences in the pe rformance of the initiators are caused by differences in the initiation mec hanism, chain growth mechanism, or side reactions. ROP of lactones was exte nded to block- and graft copolymerization with polylactones, polylactides, and polyolefins either by simply utilizing living polymer chain ends, by tr ansformation of living polymer chain ends, or by usage of polyinitiators.