Functional Design for Biodegradable Polyesters Containing Cyclic Ether Structure in Their Main Chains

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Polyesters 1a-1e and 2 with acetal-ester linkages were synthesized by the cationic ring-opening polymerization of the corresponding bicyclic lactones. Polyester 3 of etherester linkages was obtained by the direct polycondensation of the corresponding hydroxycarboxylic acid using tri-phenylphosphine and hexachloroethane as the condensing reagents. Polyesters 4a-4c having tetrahydrofuran rings in their main chains were synthesized by the titanium iso-propoxide-catalyzed polycondensation of the corresponding hydroxyesters.Hydrolytic degradation of the polyesters in a heterogeneous state was investigated at 30 ﾟC in a phosphate buffer solution (pH 7.5). The polyesters having acetalester linkages were hydrolyzed relatively easily. Polyester 1d with oxyethylene moieties in the side chains was completely hydrolyzed in five days due to enhanced hydrophilicity. Polyester 2 was degraded as rapidly as 1d. Introduction of a small amount of pendant carboxylic groups to 1a or 1b markedly accelerated the hydrolytic degradation. On the other hand, 3 was hardly degraded in a period of 14 days. Polyesters 4a-4c containing tetrahydrofuran rings were gradually hydrolyzed. The degradabilities of 4a-4c did not significantly differ with each other. Soil burial tests at 27 ﾟC showed that films of 1a were disintegraded into fine pieces after a few weeks. The rate of degradation depended on the molecular weight or the thickness of the films.