Study On Synthesis And Degradation Of Poly (D,L) Lactic Acid

(D, L) lactic acid was used to prepare poly (D, L) lactic (PDLLA) and the degradation of PDLLA was studied in this paper.The key of indirect method to synthesize PDLLA is the preparation of intermediate (D, L) lactide (DLLA). The affections on the yield of DLLA caused by catalyst, temperature and time etc. were studied. By using ethylene glycol as diluent, the distillate temperature of DLLA was lowed and the carbonization phenomenon could be avoided, which caused the yield of DLLA increasing from 36.8% to 51.3%. The molecular weight of PDLLA prepared by this method could reach 184,000. DLLA and PDLLA was characterized and analyzed by DSC, XRD and IR.The key of direct method to synthesize PDLLA is the exclusion of H2O from reaction system. Comparing with the indirect method, the molecular weight of PDLLA prepared by direct method was lower. In order to optimize technology parameters, the affections on PDLLA molecular weight caused by catalyst, temperature, time etc. were studied.The hydrolytic degradation and thermal degradation of PDLLA were investigated. The hydrolytic degradation research results showed that the PDLLA molecular weight was first degraded, then the weight loss happened in normal saline, and the water soluble crystallizable oligomers were formed during the process of degradation. The thermal degradation research results showed that the thermal degradation of PDLLA is a random breaking process, the molecular weight was degraded at range of 100癈~250癈, only above 250癈, the weight loss was found.