Study On Synthesis Of Poly(L-Lactic Acid)

The main purpose of this thesis is to study the preparation of poly(l-lactic acid) through indirect polymerization (Lactide Ring-opeing Polymerization), including the preparation of 1-lactide, the purification of 1-lactide, and the polymerization of 1-lactide, etc.First, making L-Lactide with the method of decompression is introduced, during the process of which, a research has been conducted in the dehydration time, the influence of catalysts and the respective quantity used on the molecular mass of the intermediate 1-lactic acid oligomer, and the influence of the molecular mass of 1-lactic acid oligomer on producing 1-lactide through cracking. The result show that the molecular mass of the 1-lactic acid oligomer can be as high as 2100 within 2.5-hour dehydration, with SnCl₂ as catalyst and the quantity of catalyst be 0.5%. Thus, the gross production rate of 1-lactide can be 93.6%.Then, this thesis delves into the purification of 1-lactide. In studying the purification of 1-lactide through recrystallization, this thesis analyzes the influence of different crystallization time, different density and the times of recrystallization on the purity and yield of the recrystallized products. Others, this thesis also studies the influence of alternating the solution's concentration of different recrystallization times on the recrystallization, and puts forward the method of the mother liquid processing to improving the yield. As is proved by experiments, the polymerization standard can be attained through three times recrystallization with ethanol of the density as the solvent changed from 70% to 45%, and with the mother liquor be processed, the yield could rise at 62.7% through this method.Last, this thesis analyzes the influence of the vacuum, the reaction temperature, the reaction time and the quantity of catalyst (Sn(Oct)₂) used on the molecular mass of polymers produced during the process of polymerization of the purified 1-lactide. The result of experiments shows that the viscosity average molecular mass of poly(l-lactic acid) is...