In the past few decades

biodegradable polymers

especially aliphatic polyesters have been drawn much attention due to their potential applications in both biomedical materials and eco-materials. Some of aliphatic polyesters have been commercially available because of their excellent biocompatibility and biodegradability. As far as aliphatic polyesters are concerned

it is significant to develop the living polymerization methods to yield polyesters with defined chemical structure and exact molecular weight

for controlling their biodegradation rate

hydrophilicity

glass transition temperature and crystallinity. The first two sections of this review aim at reporting on the evolution of the initiators/catalytic systems

including traditional anionic and cationic ring-opening polymerization of lactones and lactides. In addition

the greener ways of controlled polymerization are addressed in detail

such as the use of enzyme as catalysts

ion liquid and supercritical CO2 as polymerization medium. In the last section

several strategies are discussed to obtain functional (co) polyesters of various architectures by preparing novel cyclic monomers.