Catalytic Ring-Opening Polymerization of Renewable Macrolactones to High Molecular Weight Polyethylene-like Polymers

The catalytic ring-opening polymerization of macrolactones to polyethylene-like polyesters was investigated using aluminum–salen complexes as the initiators. Contrary to the common understanding that high molecular weights in these reactions can only be achieved by enzymatic ring-opening polymerization due to the absence of ring tension in macrolactones, the aluminum–salen complexes produces poly(pentadecalactone)s with number-average molecular weights (Mn) of over 150 000 g/mol. Moreover, the same catalyst is also active in catalyzing the ROP of small and medium size lactones, which makes these aluminum–salen complexes highly potential catalysts for the cROP of lactones irrespective of ring size. These results show that it is possible to polymerize macrolactones to high molecular weight polyethylene-like polymers using cheap and robust metal-based catalysts. Even the so-called medium-sized lactones (ring size: 9–12) can be polymerized with a reasonably good activity to high molecular weight products, which is truly exceptional. These results complement the common theory of ring-tension-driven cROP.