Synthesis And Degradation Of Poly (Lactic Acid-co-tyrosine)

Polylactic acid （PLA） has good biocompatibility and biodegradability thatmake it extensively used in drug delivery agents, but its hydrophobicity and lackof side chain functionality that limited its application. for the two points, thispaper use tyrosine which is one of the hydrophilic amino acids to modify PLA,and explore the synthesis of the three copolymer of tyrosine, polyethylene glycoland lactic acid, and also detect the drug delivery capabilities and degradationchanges of modified polymer.The Poly（lactic acid-co-L-tyrosine） copolymers （PLA-co-Tyr） weresynthesized via directly melt polycondensation with lactic acid （D,L-LA） andL-tyrosine （Tyr） as raw material, stannous （Sncl2） as catalyst, using gradienttemperature,0.095MPa pressure conditions through direct melt poly-condensation.（PLA-co-Tyr） discusses the optimum conditions are: pressure of0.095MPa, the ratio of raw materials n （D, L-LA）: n （L-Tyr）=95:5, the catalystSncl2the amount of0.4%（mass fraction, the same below）, the polymerizationtemperature of170℃and polymerization time10h. The results demonstrate thatthe biggest weight average molecular weight of PLA-co-Tyr is2900.The copolymers were characterized by viscosity-average molecular weight,Fourier transform infrared spectroscopy （FT-IR）, nuclear magnetic resonanceanalysis（1H-NMR）, glue permeation chromatography （GPC）, differentialscanning calorimetry thermal analysis （DSC）, condensate thermal gravimetricanalysis （TGA）, X-ray diffraction （XRD） analysis. The results demonstrate thatthe new copolymer has lower Tg and crystallinity compared with PLA. Becauseof reducing the regularity of the poly （lactic acid） is conducive to degradationand each polymer with good thermal stability. Its decomposition temperature ismore than180℃. By controlling the amount of the tyrosine, the crystallinity ofthe copolymer can be adjusted.The poly （lactic acid-tyrosine-polyethylene glycol）（PLA-Tyr-PEG） weresynthesized via directly melt polycondensation with lactic acid （D,L-LA）, polyethylene glycol2000（PEG） and L-tyrosine （Tyr） as raw materials, stannous（Sncl₂） as catalyst, using gradient temperature,0.095MPa pressure conditionsthrough direct melt polycondensation. The copolymers were characterized byFT-IR,¹H-NMR, GPC, DSC, XRD and SEM. The results showed that: theresults obtained by FT-IR and1H-NMR （PLA-Tyr-PEG） copolymer wassynthesized successfully; in a certain range with the volume of PEG increase, themolecular of PLA-Tyr-PEG which obtained by direct melt polycondensation wasdecreased, the glass transition temperature and crystallinity of the polymerdecreases with the content of PEG increase, basically lower than thePLA-co-Tyr.The degradation experiment of PLA-co-Tyr and PLA-Tyr-PEG were carriedout in phosphate buffer solution（PBS） at37℃,using PLA as the controlsample.Detect the change of water absorption and weight loss rate withPLA-co-Tyr and PLA-Tyr-PEG.Compared with Polylactic acid （PLA）, Thecopolymers have superior performance degradation. Scan electronic microscope（SEM） and XRD were used to analyze the results of degradation.The resultsshowed that: the modified polymer molecular weight with degradation timeextend to quickly lower and the crystallinity significantly reduce the degree ofobvious changes in morphology, the polymer within the hollow.Norfloxacin for the target drugs, the determination of modified polymers ondrug release properties, the results showed that compared with the polylactic acidcarrier, the modified polymer carrier release slowed down, tend to completelyrelease the total The average daily release is more stable release is superior tounmodified polylactic acid.