Catalytic ring opening polymerization of lactones, carbonates, ethers, morpholine-2,5-diones and anhydrides and catalyst therefor

The invention relates to a method for the catalytic ring opening polymerization of lactones, carbonates, ethers, morpholine-2,5-diones and anhydrides comprising contacting these compounds under polymerizing conditions with at least one metal coordinating compound initiator and at least one co-initiator, wherein the co-initiator replaces at least one ligand of the metal coordinating compound by a replacement ligand, which is less sterically hindering, in order to form a catalytic unit, so that the active part of the catalytic unit formed in this way is capable of approaching easier the compound undergoing catalytic ring opening.