Controlled random copolymerization of rac-lactide and ɛ-caprolactone by well-designed phenoxyimine Al complexes

Tong Shi, Wenlong Luo, Shaofeng Liu, Zhibo Li

Index: 10.1002/pola.28932

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Abstract

ABSTRACT The random copolymers poly(LA-ran-CL) have improved properties of degradability, mechanical strength, elasticity, and permeability over the PLA and PCL homopolymers. However, the synthesis of such copolymers is still a great challenge in polymer chemistry. In this contribution, we develop a simple but well-designed phenoxyimine Al complex (4) with bulky Ph2CH groups, which achieves controlled random copolymerization of rac-LA and ɛ-CL in a living manner (Ð = 1.06–1.09). The reactivity ratios of rac-LA and ɛ-CL (rLA and rCL) are 1.09 and 1.05 and the average sequence lengths of the lactidyl unit (LLA) and the caproyl unit (LCL) are in the range of 1.9–2.0 at different stages of conversion. In marked contrast, Al complexes (1–3) having less bulky substituents on the ligands only produce gradient copolymers. Furthermore, this strategy of catalyst design would be readily extended to other catalytic systems including β-ketiminato Al complex (5). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017. Well-designed phenoxyimine Al complex with bulky steric Ph2CH groups could achieve strict random copolymerization of rac-LA and ɛ-CL. The reactivity ratios of rac-LA and ɛ-CL (rLA and rCL) are 1.09 and 1.05 as measured by NLLS method. The average sequence lengths of the lactidyl unit (LLA) and the caproyl unit (LCL) of resulted copolymers are in the range of 1.9–2.0 as indicated by 13C NMR spectroscopy.