A renewed interest in aliphatic polyesters has resulted in developing materials important in the biomedical and ecological fields. Mainly materials such as PLA and PCL homopolymers have so far been used in most applications. There are many other monomers which can be used. Different molecular structures give a wider range of physical properties as well as the possibility of regulating the degradation rate. By using different types of initiators and catalysts, ring-opening polymerization of lactones and lactides provides macromolecules with advanced molecular architectures. In the future, new...