Study On The Molecular Wcight And Structual Control Of Polylactide Acid By Melt Polycondensation

Polylactic acid (PLA) is a kind of natural cyclation polyesters which bears wonderful biologic compatibility and biodegradable properties. It has been the research focus of macromolecule chemistry.The study on the conventional produce of PLA by a ring-opening polymerization has shown that:this methtod is expensive and complicated for it includes many time-consuming and funds-consuming processes. As having carboxyl and hydroxide, lactic acid accords with the main qualification of the direct condensation polymerization. It can control the molecular weight and structure of polylactic acid. Study on the synthesis of polylactic acid by low-cost technology to realize its widely used.First of all, using optically active L-lactic acid as material, the melt condensation polymerization condition for the polylactic acid had been discussed such as catalyst, the reaction time, the reaction temperature and remain pressure. The results showed that the ladder temperature and remain pressure controlling greatly improved the molecular weight of PLA.Secondly, polylactide acid is still limited in applications due to its intrinsic brittleness, poorly processing thermal stability and defectly product durability. The appropriate chain-extender and modifier could shorten the polymerization time effectively and increase the molecular weight of polylactic acid. At the same time, the crystalline and hydrophilicity has been changed and the functional groups been increased, that can accord with the application of PLA.Using Sn(Oct)2 as catalyst, TPPi/PEG as chain extender and modificater, the homopolymeric polylactic acid is directly synthesized via the melt copolycondesion, which had higher molecular weight and better polymers flexility and hydrophilicity. The copolymerization condition has been studied such as dosage of chain extender and modificater, the reaction temperature and the reaction time. It can get a good comprehensive properties of polylactic acid copolymer material.Then, several instruments such as infrared (IR), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and transmission electron microscope (TEM) have been empolyed to investigate the structure-properties relationship of PLLA prepolymer and chain-extended PLLA.Study on the relationship between molecular weight and structure of polylactic acid degradation of the material with the biological degradation experiment. According to its application requirements, polylactic acid copolymers were synthesized by molecule design in oder to modify its properties by introducing some functional groups that could control copolymers biodegradation.