Research On Synthesis Of Lactic Acid Prepolymer By Melt Polycondensation And Its Chain Extension

In this thesis, the synthesis of Polylactic acid and its chain extension, the properties of PLA, the applications of PLA and the modification of PLA were reviewed.We studied the reaction condition of synthesis of lactic acid prepolymer by melt polycondensation in detail. We probed into the effect of reaction time, reaction temperature and catalyst content on the molecular weight of lactic acid prepolymer, and got the optimal reacion condition. The viscosity average molecular weight of lactic acid prepolymer reached 10 344 when degree of vacuum, reaction time, reaction temperature, and Sn(Otc₂) content is 100Pa, 10h, 170℃, 1wt%, respectively.Hydroxyl terminated lactic acid prepolymer was synthesized by melt polycondensation of L-lactic acid added a little of ethylene glycol. We first synthesized telechelic poly(ethylene glycol) (PEG) by reacting PEG with isophorone diisocyanate (IPDI), then prepared PLLA/PEG multiblock copolymers by coupling reactions between PEG telechelic oligomer and hydroxyl terminated lactic acid prepolymer. What's more, We probed into the effect of various reaction conditions on the chain extension reaction. The viscosity average molecular weight of PLLA improved from 9 860 to 42 865 when catalyst content, reaction teperature, and reaction time is 0.2wt%, 150℃, 20min, respectively.Carboxyl terminated lactic acid prepolymer was synthesized by reacting succinic anhydride with L-lactic acid prepolymer prepared by melt polycondensation. Then the copolymers were prepared by chain extension of carboxyl terminated lactic acid prepolymer with DGEBA. What's more, We probed into the effect of various reaction conditions on the chain extension reaction. The viscosity average molecular weight of PLLA improved from 10 740 to 87 900 when TBAB content, reaction teperature, reaction time, and mol ratio of carboxyl terminated L-lactic prepolymer to DGEBA is 1wt%, 150℃, 30min, and 1:1, respectively; while gel content of PLLA/DGEBA copolymer is almost zero.In addition, this thesis studied and synthesized a low molecular of difunctional epoxy resin. Then used this epoxy resin as chain extender to react with carboxyl terminated lactic acid prepolymer successfully. The viscosity average molecular weight of PLLA improved from 10 340 to 33 600 when TBAB content, reaction teperature, reaction time, and mol ratio of carboxyl terminated L-lactic prepolymer to epoxy resin prepared by ourself is 1wt%, 150℃, 30min, and 1:1, respectively.In this thesis, the lactic acid prepolymers and its copolymers were charaterized by FTIR, DSC, SEM, etc.