Efficient synthesis of polylactide and copolymers under industrial conditions by multinuclear β-ketoimide zinc complexes

Polylactic acid (PLA), as a representative degradable aliphatic polyester, has the advantages of biodegradability, biocompatibility, good thermal and mechanical properties. The industrial production of high molecular weight PLA is from the the ring opening polymerization (ROP) of L-lactide (L-LA) catalyzed by Sn(II)2-ethyl-hexanoate (Sn(Oct)2) under melt and bulk conditions. Although huge efforts have been paid to develop organometallics with low toxicity and many highly active catalyst under laboratory mild conditions were found, very few candidates can compete with Sn(Oct)2 under industrially relevant conditions. Here, we reported novel multinuclear β-ketoiminate zinc complexes, as efficient catalysts for the L-LA polymerization under industrially relevant conditions, with a turnover frequency as high as 5880 h-1. The catalysts exhibited good stability and activity and compete well with Sn(Oct)2 under industrial conditions, affording colorless PLLA with high crystallinity. Preliminary copolymerization experiments suggested that the zinc catalyst can also catalyze the random copolymerization of L-LA with ε-caprolactone and dioxanone under melt and bulk conditions.