A series of aluminum complexes supported by β-ketoamino, ligand-bearing, 3-position substituentsLAlEt2 (L=CH3C(O)C(Cl)=C(CH3)NAr (L1), L=CH3C(O)C(H)=C(CH3)NAr (L2), L=CH3C(O)C(Ph)=C(CH3)NAr (L3), and L=CH3C(O)C(Me)=C(CH3)NAr (L4), Ar=2,6-iPr2C6H3) were synthesized in situ and employed in the ringopening polymerization (ROP) of ε-caprolactone (ε-CL) and cyclohexene oxide (CHO). The 3-position substituents on the β-ketoamino ligand backbone of the aluminum complexes influenced the catalyst activity remarkably for both ROP of ε-CL and CHO. Aluminum β-ketoamino complexes displayed different catalytic behavior in ROP of ε-CL and CHO. The order of the catalytic activity of LAlEt2 was L1AlEt2>L2AlEt2>L3AlEt2>L4AlEt2 for ROP of ε-CL, being opposite to the electron-donating ability of the 3-position substituents on the β-ketoamino ligand, while
the order of the catalytic activity for ROP of CHO was L1AlEt2>L3AlEt2>L4AlEt2>L2AlEt2. The effects of reaction temperature and time on the ROP were also investigated for both ε-CL and CHO.