DEVELOPMENT OF NEW BIODEGRADABLE POLYMERS

In this work, we have synthesized the copolymers of a new optically active lactone {(R)- or (S)-3-methyl-4-oxa-6-hexanolide (MOHEL), which corresponds to the lactone derived from 3-hydroxybutyric acid (3HB) and ethylene glycol} with cyclic esters {epsilon-caprolactone (CL), delta-valerolactone (VL), beta-propiolactone (PL), and L-lactide (LA)}, the copolymer of the cyclic carbonate {2,2-dimethyltrimethylene carbonate (DTC)} with CL or LA, and the homopolymers of these monomers using general ionic catalysts (AlEt(3)-H2O etc.) or an organolanthanide complex catalyst. First, we have measured some properties (such as thermal properties) of the above polymers, then we investigated the biodegradability of the polymers by activated sludge, seawater, and enzymes. Among the polymers examined, it was the (R)-MOHEL/CL copolymer (especially the copolymer containing CL unit more than 50 mol%) that was degraded significantly under every degradation condition. The biodegradability of the polymers was strongly dependent not only on the chemical structures and properties of the polymers themselves such as optical activity, molecular weight, melting point, and crystallinity, but also on the substrate specificity of exoenzymes. The H-1 NMR and mass spectroscopic analyses for the products of (R)-MOHEL/CL (=15/85) copolymer degraded by esterase revealed that most of the copolymer was ultimately degraded into the hydroxy acid of CL (viz., 6-hydroxycaproic acid).