Study On Lactic Acid-glycolic Acid Copolymer And Its Extended Chain Reaction

In this thesis, the PLGA were synthesized via direct melt co-polycondensation, by using L-lactic acid (L-LA) and glycolic acid (GA) as staring materials. At the same time, the 4,4-diphenylmethane diisocyanate (MDI) or hexamethylene diisocyanate (HDI) was used as a chain extension agent to increase the molecular weight of polymer, which the chain extension reaction of PLGA was carried out in melt state. The molecular weight of copolymers were identified through viscosity test, end-group titration and laser light scattering method. Reference to the structure and properties of polymers, which was characterized with FT-IR, 1H-NMR, DSC and TGA.The results indicated that, the intrinsic viscosity ([η]) of PLGA was doubled or more (2.05 and 2.82 times, respectively) in the same condition (-NCO/-OH=4∶1 (mol ratio); time: 20min; temperature: 160℃) when used MDI or HDI as chain extension agent. In addition, at the same condition, a number-average molecular weight by end-group titration copolymer is up to of 50,000, and by laser light scattering method the weight average molacular weigth of copolymer could reach 51300.It also can be found that, the PLGA which was using L-lactic acid (L-LA) and glycolic acid (GA) as staring materials, and synthesized via direct melt co-polycondensation with different molar feed ratio, in the chain extension reacted with 4,4-diphenylmethane diisocyanate (MDI) which was as a chain extension agent, the probability of the reaction of chain extension was enhanced with increased of the molar feed ratio of LA.IR spectra showed that the polymer ester bond is formed in the melt copolymerization stage, and isocyanate bond come into being in the process of chain expanding reaction. The result of 1H-NMR spectra showed that, the ratio of GA composition in PLGA copolymer is more than the feed ratio, which means in the reaction process, the reactivity of GA is greater than LA. Differential scanning calorimeter test structure indicated that, with the increase of GA content, the glass transition temperature of PLGA heightened, and the glass transition temperature of the the chain extended copolymer is higher than the former. Thermal stability test instrument (TGA) test results showed that, with the GA increased, the thermal stability of PLGA could be higher, even better than the one before the chain extended reaction.