Schiff Base - Transition Metal (d) / Mixed Metal Catalyst (df) And Ring-opening Polymerization Of Lactide,

Polylactide, with the characteristic properties of high mechanical strength, flexibility, chemical inertness, degradability and easy processability besides the biocompatibility, could be well used in the fields of biomedical polymer materials and medicines, while the molecular design of needed polymerization catalysts, which endows the properties for the obtained polymers from the sizes of molucular weights, the distributions of molecular weights and the microstuctures, has continuously been a big challenge to the polymerization.This thesis designed and synthetised a series of achiral or chiral Salen type Schiff-base compounds from the condensation reactions from aldehydes and diamines, and from which by the further coordination reaction with late transition metal ions (Cu2+or Ni2+) and/or rare earth metal ions (Ce3+, Nd3+. Sm3+, Eu3+, Tb3+, Ho3+ or Tm3+) obtained four series of distinctive catalysts:achiral single-site catalysts,chiral single-site catalysts,achiral double-sites catalysts and chiral double-sites catalysts. The structures of all the catalysts were characterized by the infrared spectra (FT-IR), the nuclear magnetic resonance spectra (NMR), the ultraviolet visible absorption spectra (UV-Visible absorption) and the X-ray diffraction analyses (XRD). From the bulk solvent-free melt ring-opening polymerization of L-lactide or racemic D,L-lactide catalyzed by the above mentioned catalysts, the resulting polymers were characterized by the FT-IR, NMR ('H NMR or 13C NMR) or TGA (thermogravimetric analysis), and their molecular weights (Mw or Mn) and molecular weight distributions (PDI) were determined by gel permeation chromatography (GPC) with polystyrene as standard. The correlation of the molecular structures versus the catalytic activities showed that the designed catalysts could as expected efficiently catalyze the ring-opening polymerization of lactide, with moderate molecular weights and narrow molecular weight distributions in the controllable mode.Firstly, ten achiral single-site catalysts from the late transition metal (Cu2+ or Ni2+) complexes based on different Salen-type Schiff-base ligands were obtained, and their ring-opening polymerization behaviors of L-lactide or racemic D,L-lactide were checked in detail. The catalytic results showed that structural characters of the catalysts, such as the conjugation effect, the push-pull electronic effect, the steric effect or the type of active centers, were the important and influential factors contributing to the catalytic activities.Secondly, four chiral singer-site catalyst from the late transition metal (Cu2+ or Ni2+) complexes based on different chiral Salen-type Schiff-base ligands were obtained, and their ring-opening polymerization behaviors of L-lactide or racemic D,L-lactide were studied. The results showed that efficient and controllable ring-opening polymerizations of lactide were gotten.Thirdly, with the the late trasition metal achiral complex as the precursor, eight double-sites catalysts were obtained from the involvement of rare earth ions (Ce3+, Nd3+, Sm3+, Eu3+, Tb3+, Ho3+ or Tm3+), and their molecular structures were characterized by the EA (element analyses), FT-IR and XRD. The behaviors of their catalytic polymerization on L-lactide showed that the presence of the second active center was apt to the improvement of the efficiency and the controllability from the ring-opening polymerization of L-lactide.Fourthly, from the reaction of the designed late trasition metal chiral complex with the Ln(NO3)3 (Ln3+= Ce3+, Nd3+, Sm3+, Eu3+, Tb3+, Ho3+ or Tm3+), seven double-sites chiral catalysts were obtained and used for the ring-opening polymerizations of L-lactide. The results showed that the polymerization difference was attributed to the different types of selected rare earth ions.In addition, from the viewpoint of the polymerization process, the series of factors, such as temperature, the ratio of monomer versus catalyst or reaction time were studied, respectively, and the optimized polymerization condition was founded on the design of the orthogonal test for the selected four catalysts (B1,B2,C1,C4).