Synthesis,Characterization And Properties Of Star-shaped Poly(Glycolic Acid) Via Phase Transfer Catalysis

Polyglycolic acid (PGA), a kind of synthetical aliphatic polyesters, bears nontoxicity, wonderful biologic compatibility and biodegradable properties, which is harmless and non-toxic to the environment. Compared with linear polymers, star-shaped polymers have lower crystallinity, melt viscosity, molecular surface have a higher functionality, smaller size and other properties of fluid dynamics. Therefore, we can obtain a higher molecular weight in the lower viscosity, and at the same time, such a polymer can facilitate production and processing. It is necessary to research and develope simple process, good solubility, low-cost and more practical value of the star-shaped polyglycolic acid.Chain-growth polycondensation in solid-liquid phase was used to synthesize linear polyglycolic acid with exact chemical structure, controllable molecular weight and predictable polydispersity under the mild condition. The polymerization proceeded in living fashion without any side reactions. The optimum polymerization conditions was investigated and then got the best synthetic condition. PGABr was synthesized with potassium 2-bromoacetate as the monomer, benzyl bromide as the initiator,10 mol% 18-crown-6 as the catalyst, and acetone as the solvent. Polymerization temperature is 25℃, and polymerization time is 12 hours.The structure of the polymer was confirmed by characterization with nuclear magnetic resonance (NMR), fourier transform infrared spectroscopy (FT-IR) and time of flight mass spectrometer (MS-TOF). The degree of PGABr was in agreement with the feed ratio of monomer to initiator. The polymer, which was only composed of heptmer, octamer and nonamer, possessed a narrow molecular weight distribution.With the synthesis of PGABr as a reaction model, polycondensation of potassium 2-bromoacetate, dispersed in acetone, was carried out with 1,3,5-Tris(bromomethyl)benzene as the initiator and 10 mol% 18-crown-6 as the catalyst to yield the star-shaped polyglycide acid(sPGABr). The end groups could be designed according to the structures of the end-capper. In the study, the vinyl was introduced into the star-shaped polymer backbone as the end groups, which would be modified or crosslinkede for adjusting the polymer properties. The prepolymer with allyl end groups (AllylsPGA) was easily thermal-crosslinked using allyl acrylate (AA), methyl methacrylate (MMA), n-butyl acrylate (BA) and styrene (St) as the crosslinker, and the products were uniform, white and opaque. The gels, directly obtained via thermal-crosslinking, possessed biodegradability in phosphate buffer solution at 37℃.Tumor targeting drug carrier sulfadiazine-polyglycide (sPGA-SF) was successfully synthesized by the method of phase transfer catalysis (PTC). The synthesized polymer was detected by 1H-NMR,DSC and X-ray diffraction etc. The introduction of sulfadiazine to sPGABr can result in a decrease in crystallinity. The changing of Tg is from 5.9 to 7.5℃and Tm is from 169.6 to 132.6℃, respectively.