Preparation of High-Molecular-Weight Poly(glycolic acid) by Direct Melt Polycondensation from Glycolic Acid

Relatively high molecular weight poly(glycolic acid)(PGA) was prepared by improved melting polycondensation of glycolic acid. Firstly, two kinds of catalyst, zinc acetate dihydrate and tin dichloride dehydrate, were utilized respectively, and a selection was made according to the molecular weight of final product. It has been found that the tin catalyst was the better one. Then the catalyst usage, the heating program, the polymerization time, as well as the vacuum condition were optimized. It was found that the high vacuum at 220~230°C contributed much to the molecular weight to the polymer, however, the polymerization time should be less than 1.5hr to avoid the discolor of the product. Finally, the PGA with a weight average molecular weight of 45,000g/mol were obtained directly without solid phase polycondensation, which was rather higher than some reported previously. The structure and properties of PGA were also characterized by means of intrinsic viscosity, FTIR, NMR and DSC testing.