Ring-Opening Polymerization of epsilon-Caprolactone and Cyclohexene Oxide Initiated by Aluminum beta-Ketoamino Complexes:Steric and Electronic Effect of 3-Position Substituents of the Ligands

摘要

A series of aluminum complexes supported by beta-ketoamino,ligand-bearing,3-position substituents LAlEt2(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 ring-opening polymerization(ROP)of epsilon-caprolactone(epsilon-CL)and cyclohexene oxide(CHO).The 3-position substituents on the beta-ketoamino ligand backbone of the aluminum complexes influenced the catalyst activity remarkably for both ROP of epsilon-CL and CHO.Aluminum beta-ketoamino complexes displayed different catalytic behavior in ROP of epsilon-CL and CHO.The order of the catalytic activity of LAlEt2 was L1AlEt2>L2AlEt2>L3AlEt2>L4AlEt2 for ROP of epsilon-CL,being opposite to the electron-donating ability of the 3-position substituents on the beta-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 epsilon-CL and CHO.