Syntheses of Biodegradable Polyesters and Effect of Chemical Structure on Biodegradation

Abstract

Syntheses and biodegradation of aliphatic polyesters were studied. Polymers synthesized were copolyesters of L-lactide with lactones, copolyesters derived from γ-butyrolactone (BL), polyesters having alcoholic OH group, and copoly (ester/ether)s of oxiranes with lactones. γ-Butyrolactone copolymers were obtained by transesterification reaction, and the maximum BL content was around 30%. Polyesters having alcoholic OH group were prepared by the polyaddition of aliphatic diglycidyl ester compounds with several aliphatic dicarboxylic acids. The alcoholic OH group is susceptible to acylation. To develop biodegradable functional polymers, polyesters having alcoholic OH group as a side chain were found to be essential. Biodegradation was mainly evaluated by enzymatic hydrolysis concerned with the chemical structure. Hydrolysis was influenced by copolymer composition, lengths of methylene chain in the backbone, and substituents. The biodegradability shows the maximum at a certain composition depending on the ester content, the randomness, and crystallinity. The methyl side group in the polymer chain suppresses the degradation. The copolymers having long methylene chains (n = 3–5) have high biodegradability because of flexibility of the polymer chain. Hydrophilicity promotes biodegradability. Ester group in a side chain was found to be more biodegradable compared to that in main chain.