L-polylactic Acid Polymer Material And Its Degradation Characteristics

For the shortcomings of poly-lactic acid (PLLA) especially used as biomedical materials, such as low number-average molecular weights (Mn), and toxic catalyst residue, this thesis is focused on the development of new catalysts with lower toxicity, better biocompatibility and higher catalytic activity for the formation of PLLA with higher number-average molecular weights and shorter PDIs (PDI= Mw/Mn).Firstly, based on the selected Salen-type Schiff-base ligand H2L, its self-assembly of with Zn(OAc)2·2H2O?Ln(OAc)3-6H2O (Ln= La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu) is expected to obtain the series of hetero-binuclear complexes [Zn(L)(?-OAc)Ln(?2-OAc)2] (Ln= La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu), respectively. Besides the characterization of EA, FT-IR,1H NMR and ESI-MS for these complexes, their thermal stabilities need to be checked.Secondly, with the purified L-lactide as the starting material, the series of hetero-binuclear complexes [Zn(L)(?1-OAc)Ln(?2-OAc)2] (Ln= La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu) are used as the catalyst, and their detailed catalytic behaviors to obtain PLLAs are explored.Finally, based on the preliminary degradable study of the obtained PLLAs in the same agenet or different agents, the relationships with the micro-structural charcters of PLLAs and the suitable agents are also anticipated.The primary conclusions from the job above were shown as follows,(1) Firstly, through the self-assembly of H2L with Zn(OAc)2-2H2O? Ln(OAc)3-6H2O (Ln= La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu), the series of complexes [Zn(L)(?1-OAc)Ln(?2-OAc)2] (Ln= La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu) were successfully obtained in good yields, respectively. The characterization results of EA, FT-IR,1H NMR and ESI-MS showed their similar hetero-binuclear structure. On the other hand, their thermal stabilities showed that they could be stable on the temperature of 200?.(2) Using each of the series of hetero-binuclear complexes [Zn(L)(?1-OAc)Ln(?2-OAc)2] (Ln= La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu) as the catalyst, it could effectively catalyzed the ring-opening polymerization of L-lactide on the condition of solvent-free melt. In addtion to the good controllable character (PDI<1.10), the L-lactides were almost completely consumed, and the Mn values could be up to 105 g/mol. Moreover, for the catalyst, the optimized polymerization procedure, such as the molar ratio 4000:1 of monomer to catalyst, the polymerization time of 4 h) and the polymerization temperature of 130 ? was exhibited. Furthermore, the effects of introduction of co-catalyst (BnOH or i-PrOH) and the lanthanide contraction on the detailed catalytic behaviors were also be explored.(3) The degradable abilities of the obtained PLLAs were showed to be relative to both the micro-structures of PLLAs and their surround agents, and the acidity of agents were showed to be helpfue for the degradity.