Multinuclear catalysts for the ring-opening polymerisation of cyclic esters

The global production of polymers continues to increase annually, with plastics utilised in an ever-widening field of application. The majority of plastics are still derived from fossil fuels and are not biodegradable, giving rise to the well documented environmental problems associated with plastic. To utilise more sustainable resources, and create polymers which degrade more readily in the environment, attention has recently shifted to materials, such as poly(lactic acid) (PLA), that can be derived from renewable monomer feedstocks. The ring-opening polymerisation (ROP) of cyclic esters is the most widely studied route to sustainable polymers and is often catalysed using metal complexes. Many of the reported catalysts are monometallic species but more recently the potential for beneficial cooperative effects between multiple metal centres has led to increased activity in the study of multinuclear catalysts. Here we explore the most recent developments in the application of multinuclear catalysts to the ROP of cyclic esters examining the relationships between structure and activity, organised by the metallic elements involved.