Progress of Ring-Opening Polymerization of Cyclic Esters Catalyzed by Iron Compounds

Aliphatic polyesters such as polylactide (PLA) and polycaprolactone (PCL) have attracted much attention due to their prominent features of environmentally friendly materials with good biocompatibility and biodegradability. The commercialized PLA and PCL materials have been commonly prepared at high temperature using tin octanoate as catalysts: however, a higher temperature of polymerization potentially causes broader dispersity or/and lower molecular weight of the resultant polymers; most importantly, residual tin catalysts in the polymer products may be harmful to mammals and/or other living organisms in the ocean. As an abundant metal in the earth, not only is iron an essential element in the human body but also its compounds play important roles in pharmaceutical and polymerization chemistry. Recently, iron-based compounds have been proved to be efficient promoters of ring-opening polymerization of cyclic esters under mild conditions. Herein the progress of iron compounds used for the ring-opening polymerization (ROP) of cyclic esters is reviewed in order to develop practical catalysts for industrial processes in the future.