| In this dissertation, the preparation processes of PLA by ring-opening polymerization of lactide and the degradation of PLA obtained were studied.During the studying of ring-opening polymerization of lactide to prepare PLA, using lactide made in lab as raw material, the method of recrystallizing and purifying lactide, the technologic conditions of synthesizing high relative molecular weight PLA, and the stability of catalyst were investigated. The results showed that, melting point of high yield lactide made in the lab reached 127℃after three times of recrystallization, and the yield of lactide reached 57.2%. Using the toluene solution of Sn(Oct)2 (0.05mol Sn(Oct)2/1L toluene) as a catalyst, the better technologic conditions were: using 3g lactide as raw material, 1/1000 mole ration of catalyst Sn(Oct)2 to lactide, vacuity 0.098MPa, polymeric temperature 130℃and polymeric time 7h as polymerization conditions, the relative molecular weight of the synthesized PLA could reached 1,017,000. The function of the catalyst didn't change obviously for 7 days after preparation.Using PLA synthesized by the technologic conditions described above as raw material, the degradation processes of PLA pellicles in the PBS fluid were investigated. Taking the mass and the relative molecular weight of PLA as assessing standard, the tendency of decomposing PLA were found through experiments of accelerating time test and real time test. The result showed that, during the degradation of PLA, the mass of PLA reduced almost at the constant rate, while the relative molecular weight reduced fast in the early time and then became slowly.Finally IR, NMR and TGA were used to characterizing the products. |
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