Synthesis And Catalytic Properties Of β-Diketiminate Aluminium Complexes

Poly(ε-caprolactone) (PCL) has been applied widely in biomedical and pharmaceutical industry such as long-term drug delivery systems, scaffolds in tissue engineering and suture, mainly due to their special mechanical properties, biocompatibility and controlled biodegradability. PCL with high molecular weight is mainly synthesized by ring-opening polymerizations initiated by metal complexes. Although many catalysts have been investigated, the catalytic systems which have high activity and can control molecular weight well are still rare. Therefore researchers endeavor to explore novel catalysts which possess the characteristics of good biocompatibility, high catalytic activity and stereoselectivity.The steric and electronic effect ofβ-diketiminates can be regulated through changing the N-substitute groups. They can coordinate with most of the main group, transition and rare-earth metal, which can be employed in intramolecular hydroamination, olefin polymerization and ring-opening polymerization of cyclic eaters.With the view of designing and synthesizing new catalysts for ROP ofε-caprolactone, four N-aliphatic-β-diketiminate aluminium complexes were prepared by the treatment of trimethyl aluminium respectively with nacnacBnH(Bn=CH2Ph), R,R-nacnacCH(Me)PhH, rac-nacnacCH(Me)PhH and S, S-nacnacCH(i-Pr)PhH. They were characterized by 1H NMR,13C NMR, EI-MS and X-ray analyses.The obtained four aluminium complexes all can initiate the ROP ofε-CL, among which R,R-nacnacCH(Me)PhAlMe2 shows the highest activity with high number-average molecular weight and narrow distribution for its resulting ROP products. The kinetic experiments show that the molecular mass of the resultant polymer increase linearly with the conversion of monomer, indicating a living polymerization feature. In the optimized conditions (toluene,110℃), PCL with Mn=5.9×104 and Mw/Mn=1.17 was synthesized.