Ring-opening homo- and co-polymerization of lactides and ε-caprolactone by salalen aluminum complexes

Aluminum complexes of non-chiral-salalen ligands were investigated in the catalysis of ring-openingpolymerization (ROP) of lactide and ε-caprolactone and in their copolymerization. The aluminum-salalencomplexes were found to polymerize all varieties of lactide, namely: L-, D-, rac- and meso-lactide, andshowed moderate productivities. rac-LA gave rise to isotactic polylactides (with Pm up to 72%), whilemeso-LA gave rise to heterotactic polylactides (with a Pm of 79%). An experiment was designed for distinguishingbetween chain-end control and enantiomorphic-site control combined with polymerylexchange for the isotactic stereoblock microstructure observed for the PLA produced from rac-LA; itgave strong evidence for polymeryl exchange between propagating species. Finally, this class of catalystspromoted the copolymerization of ε-caprolactone and lactides. In particular, compound 2b allowed controlledrandom copolymerization of ε-caprolactone and L-lactide