Lactide Polymerisation with Complexes of Neutral N-Donors - New Strategies for Robust Catalysts

Ring-opening polymerisation of cyclic esters represents a growing field of research, because the resulting polymers are biodegradable and mostly based on renewable raw materials, which ensures increasing interest in this process within the context of green chemistry. Up to now, neutral N-donor ligands have been overlooked in their potential to stabilise catalytically active systems. This contribution summarises recent developments in this area as well as their applicability in lactide polymerisation with special regard to the reaction conditions. When a use on the industrial scale is targeted, tolerance towards moisture, air, lactide impurities and high temperatures is an important issue to be considered during catalyst design. A multitude of sodium, calcium and zinc complexes with amines, carbenes, guanidines, phosphinimines, pyridines and tris(pyrazolyl) methanes is discussed and their activity in lactide polymerisation is highlighted.