Abstract
Firstly, we have synthesized the cyclic depsipeptides from amino acids and DL-2-bromopropionyl bromide (a hydroxy acid derivative). The amino acids used were L-alanine, L- (DL- or D-) valine, and L-leucine. The depsipeptides obtained were abbreviated as DMO, PMO, and BMO in the order of these amino acids. Subsequently, homopolymers of the depsipeptides and their copolymers with ε-caprolactone (CL) were prepared using tin (II) octylate as a catalyst. The results for the measurements of thermal properties and NMR spectra of these polymers revealed that every depsipeptide homopolymer was noncrystalline, whereas depsipeptide/CL copolymers were crystalline or noncrystalline depending on the polymer composition, and had random sequences. Next, the biodegradability of these polymers by enzymes (Proteinase K, cholesterol esterase) and activated sludge was investigated. First, the degradability using Proteinase K was examined. The degradability of PMO homopolymers was in the order: Poly (L-PMO) >>Poly (DL-PMO) >Poly (D-PMO), suggesting the substrate specificity of this enzyme to be high for (naturally occurring) L-amino acids. On the other hand, for the copolymers, Proteinase K degraded them in the order: Copoly (L-DMO/CL) >>Copoly (L-PMO/CL) ≥ Copoly (L-BMO/CL), while cholesterol esterase, Copoly (L-PMO/CL) >Coply (L-BMO/CL) ≥ Coply (L-DMO/CL). The hydrophile-lipophile balance of the copolymers probably affected these results. Further, these polymers were degraded rapidly by activated sludge.
