Study On Synthesis And Modification Of Polylactic Acid

A method for synthesizing polylactic acid with heteropoly acid as catalyst, and optimizing reaction conditions of PLA's polymerization. Also basic research of synthesis copolymer PLA-PEG and P(LA-co-Gly) were probed.Firstly, the synthesis of polylactides by direct condensation polymerization catalyzed by phosphotungstic acid was studied. The structure and crystalline structure of phosphotungstic acid were determined by infrared FTIR and XRD. And the microstructure, viscosity average molecular weight of PLA were investigated by Fourier transform infrared FTIR, and viscosity meter. The comparatively appropriate reaction conditions were as follows:the content of phosphotungstic acid was 0.5wt% of lactic acid, polymerized at 170℃for 6h under a system vacuum of 1-2kPa. As a result, a certain viscosity average molecular weight was got.Secondly, the PLA-PEG block polymer catalyzed by solid super acid SO42-/ZrO2-CeO2 was prepared by opening ring polymerization. The acidic property was measured by IR spectra, Hammett Indicator and NH3-TPD techniques. The effects of molecular weight of PEG, reaction time, temperature and catalyst amount on copolymer were studied, and the characteristic group of copolymer was measured by FTIR spectra. The solid super acid SO42-/ZrO2-CeO2 had the strongest acid strength and maximal acid content roasted at 650℃. The optimum reaction conditions were obtained, which were the amount of catalyst 1.0% vs lactic, the molecular weight of PEG6000, polymerization at 170℃for 9h. The intrinsic viscosity reached 1.693dl·g-1.Lastly, the synthesis research of polylactic acid modified by a amino acid was done. With the lactide(LA) and glycine (Gly) as the stanting materials, Gly was made into the cricoid unit morpholine-2,5-dione, then LA and Gly was reacted by opening ring copolymerization, FTIR and 1H-NMR made sure the copolymer was P(LA-co-Gly). And got a comparatively appropriate reaction conditions by exploring, as follows:the content of the catalyst Sn(Oct)2 was 0.3% of that of LA, temperature was 160℃, reaction time was 8h. The viscosity reached 0.91dl·g-1, which could meet the requests for the application in drug delivery of this biodegradable material.