Iron(III) and zinc(II) calixarene complexes: Synthesis, structural studies, and use as procatalysts for ε-caprolactone polymerization

Economic pressure, environmental issues and ever increasing demand are driving the shift from oil-based polymers to those available from renewable resources. Ring opening polymerisation of cyclic esters is currently a topical field with metal complex-induced coordination/insertion type polymerisation leading the way. Such a polymerisation method offers a wide range of advantages from control over the polymer structure to kinetic enhancement; however industrially available catalysts based on tin suffer from inherent toxicity and as a result a policy change from the Food and Drug Administration (FDA) is not unrealistic. This review underlines the efforts made in the past five years or so, and shows how low toxicity metals are attracting increasing attention in the field of e-caprolactone polymerisation.