Controlled random copolymerization of <i>rac</i>‐lactide and <i>ɛ</i>‐caprolactone by well‐designed phenoxyimine Al complexes

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 Ph 2 CH 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 ( r LA and r CL ) are 1.09 and 1.05 and the average sequence lengths of the lactidyl unit ( L LA ) and the caproyl unit ( L CL ) 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. 2018 , 56 , 611–617