Random copolymerization of l‐lactide and ε‐caprolactone by aluminum alkoxide complexes supported by N2O2 bis(phenolate)‐amine ligands

The bowl‐shaped aluminum alkoxide complexes bearing N₂O₂ bis(phenolate)‐amine ligands having different side arms as pyridine ( 1 ), dimethyl amine ( 2 ), and diethyl amine ( 3 ) were shown to be highly efficient and well behaved in the homopolymerization and copolymerization of l ‐lactide (LA) and ε‐caprolactone (ε‐CL) at 100 °C. The rates of copolymerization are similar for Complexes 1 – 3 where nearly full conversions were achieved in 60 h for [LA]:[CL]:[Al] ratio of 50:50:1. The minor adjustment of the side arms of the Catalysts 1 – 3 gave profound differences in the LA/ε‐CL copolymer sequences where tapered, gradient, and highly random structures were obtained in one system, respectively. The chelation of LA to Al metal after ring‐opening process and suitable steric hindrance of the side arms were believed to participate and saturate the aluminum metal centers giving different copolymer structures. The random LA/ε‐CL copolymer structure was confirmed by nuclear magnetic resonance and differential scanning calorimetry analysis. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1635–1644