Ring-opening homo- and co-polymerization of lactides and -caprolactone by salalen aluminum complexesElectronic supplementary information (ESI) available: The COSY NMR spectrum of complex 2b; tables with a tetrad distributions analysis; a table with details of some polymerization experiments; copolymerization data for the determination of the reactivity ratios. See DOI: 10.1039/c4dt02616k

Aluminum complexes of non-chiral-salalen ligands were investigated in the catalysis of ring-opening polymerization (ROP) of lactide and -caprolactone and in their copolymerization. The aluminum-salalen complexes were found to polymerize all varieties of lactide, namely: l -, d -, rac - and meso -lactide, and showed moderate productivities. rac -LA gave rise to isotactic polylactides (with P m up to 72%), while meso -LA gave rise to heterotactic polylactides (with a P m of 79%). An experiment was designed for distinguishing between chain-end control and enantiomorphic-site control combined with polymeryl exchange for the isotactic stereoblock microstructure observed for the PLA produced from rac -LA; it gave strong evidence for polymeryl exchange between propagating species. Finally, this class of catalysts promoted the copolymerization of -caprolactone and lactides. In particular, compound 2b allowed controlled random copolymerization of -caprolactone and l -lactide. Salalen aluminum complexes gave isotactic polylactides from rac -LA, heterotactic polylactides from meso -LA and random copolymers of LA/CL. An experiment was designed to prove polymeryl exchange events.