Study On The Catalytic Behaviors Of β-diketone Ti,Zr In Ring-Opening Polymerization Of Lactide

As a kind of bio-degradable environment-friendly polymer, Poly(lactic acid) (PLA) has been used widely in many areas such as medical devices, packaging and textile, and the synthesis of PLA has also become an attractive subject. So the ring-opening polymerization (ROP) of lactide using new catalysts is valuable to be studied in academic and industrial fields.In this paper, acetylacetone titanium (Ti(AcAc)₂Cl₂, Cat1),benzoylacetone titanium (Ti(BzAc)₂Cl₂, Cat2),dibenzoylmethane titanium(Ti(BzBz)₂Cl₂ , Cat3) and acetylactone zirconium(Zr(AcAc)₂Cl₂ , Cat4) have been synthesized in a modified way. These complexes were characterized by element analysis and ¹H-NMR. In addition, these complexes were used to catalyze the ROP of lactide in bulk state and in toluene solution, respectively. In order to evaluate these catalytic systems, the influences of reaction parameters, such as catalyst, catalyst amount, monomer concentration, solvent polarity, polymerization time and temperature have been studied in detail.The results showed that the catalytic activity of Zr complexes is higher than that of Ti complexes. In addition, less steric hindrance of ligand coordinated with the metal-active center is favorable for higher polymerization conversions, higher molecular weight and broader molecular weight distribution. In bulk polymerization, conversions of monomer over 95% can be reached easily and a maximum viscosity molecular weight of 6.792 × 10⁴ can be obtained. In bulk state, both polymerization conversions and the molecular weight (MW) of PLA are obviously higher than that in solution polymerization system.