Synthesis of Bioabsorbable Aliphatic Polyesters

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The primary purpose of the present work is to accumulate the fundamental knowledge that is required for synthesis of the clinically applicable materials starting from lactic acid and glycolic acid. Much attention was paid here on investigations of factors governing the polymerization of monomers and the degradation rate of the polymers. Studies on melt spinning of poly-L-lactide fiber and the properties of the fiber were also performed in this work. The important results may be summarized as follows.First we studied general characteristics of condensation polymerization of lactic acid, along with ring-opening bulk polymerization of lactides. Stannous octoate was used as the ring-opening polymerization catalyst. The effects of catalyst concentration, polymerization time, polymerization temperature on the monomer conversion as well as the molecular weight of polymers were made clear. Experimental data were presented for determining the glass transition temperature (Tg) and melting temperature (Tm) of the lactic acid polymer with different molecular weights. The transition temperature-molecular weight relationship was examined and values of Tg and Tm at the infinite molecular weight were derived. The study was further extended to the melt spinning of poly-L-lactide lactide and the resultant fiber was characterized by measuring the tensile strength, the dynamic viscoelastic factors, and the degree of crystallinity. The effect of drawing ratio and temperature was also discussed. The results of a long-term study on the hydrolytic degradation of poly-L-lactide fiber were compared with those of a commercially available, synthetic bioabsorbable suture, Dexon.