Preparation Of Cyclic Esters And Synthesis Of Polyurethanes From PLGA/PEG/PLGA Triblock Copolymers

Biodegradable materials synthesized from renewable resource can replace petrolic plastics and be applied in the field of biomedicine. Increasing the yield of lactide and glycolide, which are the important monomers for the synthesis of biodegdadable biomaterials, is very significant in the view of academic study and technology. Invastigation of polyurethane synthesized from random copolymers from lactide and glycolide will enlarge the applied areas in field of biomedicine.This thesis optimized the technologicial conditions of synthesis of D,L-lactide and glycolide from D,L-lactic acid and glycolic acid, respectively. The preparation process consisted of three stages, i.e., dehydration, prepolymerization and depolymerization. The optimum reaction condition of D,L-lactide investigated and identified in this paper was found that the optimal dehydration temperature under normal pressure, optimal prepolymerization temperature and optimal depolymerization temperature were 140℃, 170℃and 220℃to 240℃, respectively. The yield of D,L-lactide before purification increased to 90% when Zn catalyst was 0.9wt% and added in 3 times. In accordance, the optimal temperatures of three stages of synthesis of glycolide from glycolic acid were 150℃, 190℃and 280℃, respectively. The yield of glycolide could be achieved to above 92% when antimony (III) trioxide was used as catalyst via controlling the height of the stirrer.Recrystallization and purification of D,L-lactide and glycolide were studied and modificated. Ethyl acetate and isopropanol were selected to be used as solvents for the recrystallization of D,L-lactide. When ethyl acetate was solvent, the efficiency of purification at normal temperature is lower, but the efficiency of purification round about 0℃raised to 41%. It was increased to 65% when 2-isopropanol as solvent was cooled rapidly to about 0℃. The solvent of rude glycolide was ethyl acetate. The yield of pure glycolide increased to 75% by reclaiming the mother solution.Furthermore, the synthesis of ABA-type triblock copolymers via ring-opening polymerization of D,L-lactide, glycolide andα,ω-dihydroxyl-polyethylene glycol as initiator was also investigated in this thesis. Biodegradble copolyester-urethanes were...