Biodegradation of Novel Optically Active Polyesters Synthesized by Copolymerization of (R)-MOHEL with Lactones

Biodegradations of random copolymers of ( R )-3-methyl-4-oxa-6-hexanolide [( R )-MOHEL] with various lactones such as ε-caprolactone (24/76 ratio), δ-valerolactone (22/78), and β-propiolactone (31/69) were examined with normal or acclimated activated sludge. As a consequence, the biodegradability was found to increase in the order poly[( R )-MOHEL- ran -ε-caprolactone] > poly[( R )-MOHEL- ran -δ-valerolactone] > poly[( R )-MOHEL- ran -β-propiolactone]. The mode of biodegradation of ( R )-MOHEL/lactone copolymers with enzymes (cholesterol esterase etc.) resembles that of biodegradation with activated sludge. All the copolymers degraded better than the homopoly[( R )-MOHEL] or homopoly(lactone)s. In contrast, these latter polymers are inert to hydrolytic degradation by basic or acidic buffer solution. The major biodegradation product of poly[( R )-MOHEL- ran -ε-caprolactone] (15/85) by enzymes is 6-hydroxycaproic acid as revealed by NMR spectroscopy and mass spectrometry, while the biodegradation product from poly[( R )-MOHEL- ran -δ-valerolactone] (18/82) is a linear δ-valeric acid dimer.