Synthesis Of Polylactic Acid By Melting Polycondensation

Polylactic acid (PLA), a kind of green environmental material, isbiodegradable and biocompatible. It can be obtained through differentsynthetic methods. In the recent years, Polylactic acid has been widelyused in various fields such as biomedical, packaging and spinningbecause of its biodegradability, biocompatibility and good mechanicalproperties. This thesis aims to synthesize high viscosity averagemolecular weight of PLA materials by direct melt polycondensation ofL-lactic acid. This method is easy to operate, not involving any organicsolvent during the process and more important is that it is convenient toimplement industrialization of continuous production. Polycondensationof L-lactic acid can be performed in a shorter reaction time comparing toring-opening polymerization of L-lactide. The PLLA can meet therequirements of general mechanical processing and be used inbio-pharmaceutical industry. The main works as follows:Firstly, we systematically studied various parameters of titaniumcatalysts in the polymerization by melting polyconfensation. For example,the influence of pre-polymer of lactic acid, the effect of the amount of catalyst, the molar ratio of catalyst, reaction temperature and reactiontime on the polymerization, all of them were investigated in detail. Theresults showed that binary catalysts, comprising of metal compoundsactivated with proton acids, were more effective than single-metal-compound based catalysts in bulk polycondensation, giving poly(l-lacticacid) with viscosity average molecular weight (Mv) of6×104in highyield.Secondly, we synthesized successfully15kinds of Schiff baseligands by the utilization of condensation between aldehydes and imines,and then investigated that their coordination with metal titanium. Theresults showed that only four Ti-Schiff base complexes could be activedin catalytic reaction. All of chemical structures of the compounds we hadobtained were charactered by1H NMR and13C NMR.Finally, we prepared poly(lactic acid) products by the utilization ofthese four Ti-Schiff base complexes in direct polycondensation, from theexperiment, we knew that Ti-Schiff base complex had better effect thanany other single-metal-compound, giving poly(l-lactic acid) withviscosity average molecular weights (Mv) of4×104.