Organo-catalyzed/initiated ring opening co-polymerization of cyclic anhydrides and epoxides: an emerging story

Polyesters are omnipresent in our everyday lives and their synthesis via eco-friendly methods is becoming a major challenge today. The co-polymerization of cyclic anhydrides and epoxides was first reported by Fischer in 1960 involving a tertiary amine as an initiator. Since then, metal complexes have been used as catalysts in this process, Inoue being a major contributor in this area until Coates' breakthrough using a zinc-based catalyst leading to high molecular weight polymers. Such a pathway to polyesters is the most promising method for accessing a large array of polyesters given the large pool of commercially available or easily synthesizable epoxides and cyclic anhydrides. To date, the use of metal-free organo-catalysts/initiators in this co-polymerization remains to be explored; this area is still in its infancy but interesting developments have been reported over the past five years. In this review, we provide a complete overview of such organo-catalyzed/initiated processes since 2015.