Synthesis of lactide/ɛ-caprolactone quasi-random copolymer by using rationally designed mononuclear aluminum complexes with modified β-ketiminato ligand

A series of novel aluminum complexes containing bulky aryl-β - ketiminato ligands [ArNCH  C 10 H 7 C 6 H 5 O]Al(CH 3 ) 2 ( 3a , Ar = C 6 F 5 ; 3b , Ar = C 6 H 5 ; 3c , Ar = 2,6- i Pr 2 C 6 H 3 ) have been synthesized in high yields. These complexes were identified by 1 H and 13 C NMR spectroscopy, elemental analysis, and X - ray structural analysis. All the aluminum complexes could efficiently catalyze the ROP of ɛ- caprolactone ( ɛ -CL) and Lactide (LA) in a controlled manner. It was found that the steric effect of the ligand has less effect on the ROP of CL, while the polymerization rate of L -LA was suppressed significantly. More interestingly, this kind of catalysts can promote the random copolymerization of ɛ -CL and L -LA. The transesterification side reaction and the polymer composition could be adjusted by modulating the electronic and steric effects of the ligand. In paticular, compound 3c could produce quasi-random copolymers without transesterification side reactions, as indicated by both the values of the reactivity ratios of the two monomers ( r LA = 1.31; r CL = 0.99) and the similar average lengths of the caproyl and lactidyl sequences ( L CL = 2.34; L LA = 2.44). Finally, a drug-random copolymer conjugates could be easily prepared by using 3c , indicating a potential application of 3c in pharmacutical and biomedical field. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56 , 203–212