| Polylactide (PLA) have attracted increasing interest in biomedical field due to their biodegradable and biocompatible. An efficient way to synthesize PLA is the ring-opening polymerization of lactide (LA) catalyzed by metal complexes. By careful selection of ligands and metal, reactions can be generated to form a desired polymer structure.Highly active catalyst needs not only the strong coordination ability between metal atom in catalyst and carbonyl oxygen atom in lactide but also to increase the electron density of oxygen atoms in O-M bond of catalyst; It is necessary to consider the impact of long term heat on the decomposition of metal complexes during catalytic polymerization reaction. Therefore, in order to increase the stability of complexes, nitrogen atoms with additional electrons can be considered to be introduced into metal complex and coordinate with metal atom; Taking into account the presence of side reactions such as intermolecular ester exchange reaction and intramolecular ester exchange reaction during the ring-opening polymerization of lactide, ligand with large steric hindrance can be considered to coordinate with metal atom. This type of metal complexes can reduce the incidence of side reactions, thereby decrease the polydispersity index (PDI) of polymer. Based on the above design ideas of highly active catalysts, a new titanium Schiff-base complex (Ti-Salen) was synthesized using 3, 5-Di-tert-Dutylsalicylaldehyde, ethylenediamine and tetraethyl titanate as raw materials. And then the Ti-Salen was used to catalyze bulk ring-opening polymerization of D, L-lactide. The effects of molar ratio of monomer and catalyst, the polymerization temperature and polymerization time on polymerization were studied in detail using number-average molecular weights (Mn) and polydispersity index (PDI) as evaluation indexes. The structure, thermal property, degradation behavior in vitro and biocompatibility of PDLLA obtained by ring-opening polymerization of D,L-LA using Ti-Salen as catalyst were studied. The main works and conclusions are included as follows:①The Schiff-base ligand (Salen) was synthesized by condensation reaction between salicylaldehyde which have two electron-contributing groups (t-Bu) and ethylenediamine. And then Ti-Salen was obtained by transesterification among Salen, tetraethyl titanate and equimolar of water. IR and NMR analysis showed that the N atoms of ligands had coordinated to metal Ti atoms successfully and the O atoms of ligands had formed covalent bond with metal Ti atoms. XRD, EA, X-ray single crystal and SEM analysis showed that the Ti-Salen is layered solid, crystal system of Ti-Salen is a monoclinic structure with C2/c space group, constitute a symmetric space structure with the approximate diamond plane formed by two Ti and two O linked with covalent bond as the center. The results of TG/DSC showed that the decomposition temperature of Ti-salen is 360℃, indicated this metal complex has good thermal stability.②The Ti-salen was used to catalyze ring-opening polymerization of D, L-lactide. The polymerization result showed that in the conditions of monomer and catalyst was 2600, polymerization time was 16h, polymerization temperature was 160℃, the monomer conversion of PDLLA reached its maximum value. The result of polymerization experiment also showed that the PDIs of PDLLA were all in the range of 1.09 ~ 1.24, this indicated this Schiff-base complex has relatively high catalytic activity and controllability of molecular weights in catalyzing ring-opening polymerization of D, L-lactide.③The physical and chemical properties of SP and TP obtained by ring-opening polymerization of D,L-LA using Sn(Oct)2 and Ti-Salen as catalyst respectively (The Mn of the two materials are similar and The PDI of SP is higher than that of TP) were investigated, including hydrophilicity and biodegradation.The surface hydrophilicity evaluation was based on static water contact angle and water adsorption ratio, while the actual degradation experimentation in vitro was used to estimate the biodegradation behavior. The results as follows:1) The static water contact angle of SP and TP based materials was in the sequence of SPTP. The results revealed the hydrophilic of TP is worse than SP.2) The result of degradation experiments showed the two materials had similar degradation regular pattern, but the degradation rate of TP was slower than that of SP.④The biocompatibility of SP and TP based materials with rats osteoblasts was estimated (cell morphology (SEM observation) and proliferation (MTT assay)). The results showed that the biocompatibility of TP is worse than that of SP.
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