Metal-catalyzed immortal ring-opening polymerization of lactones, lactides and cyclic carbonates.

This Perspective article summarizes efforts paid in our group to develop efficient metal-based catalysts for the immortal ring-opening polymerization (iROP) of cyclic esters in the presence of large amounts of alcohols (ROH) as chain transfer agents. The catalyst systems reviewed include discrete organometallic complexes based on rare earths, magnesium, calcium and more specifically zinc, as well as simple systems employing metal triflate salts, notably Al(OTf)(3), for the (stereo)controlled iROP of lactide (LA), beta-butyrolactone (BBL) and trimethylenecarbonate (TMC). Special emphasis is given to systems that allow the use of minute amounts of metal catalysts and large loadings of both monomer and alcohol for the rapid and productive formation of functional polyesters (H-Pol-OR) with controlled molecular features.