Highly biodegradable copolymers composed of chiral depsipeptide and L‐lactide units with favorable physical properties

Syntheses of copolymers composed of optically active depsipeptides (3,6‐dimethyl‐2,5‐morphorinedione) and L ‐lactide—poly( L ‐3, L ‐6‐dimethyl‐2,5‐morphorinedione‐ co ‐ L ‐lactide), poly( L ‐3, DL ‐6‐dimethyl‐2,5‐morphorinedione‐ co ‐ L ‐lactide), and poly( L ‐3, D ‐6‐dimethyl‐2,5‐morphorinedione‐ co ‐ L ‐lactide)—were examined in an effort to improve the biodegradability and physical properties of homopoly( L ‐lactide). In degradation tests, the copolymers composed of 3,6‐dimethyl‐2,5‐morphorinedione and lactide in the ratios 10/90 to 13/87 exhibited high biodegradability toward proteinase K, whereas a homopolymer, poly( L ‐lactide), exhibited very poor biodegradability (only 50% after 200 h). These polymers composed of 3,6‐dimethyl‐2,5‐morphorinedione/ L ‐lactide in 11/89 to 13/87 ratios also degrades rapidly after being in compost for 30 days. The resulting copolymers, however, showed relatively low elongation properties. Therefore, ternary copolymerizations of L ‐3, DL ‐6‐dimethyl‐2,5‐morphorinedione, ϵ‐caprolactone, and L ‐lactide were explored in an effort to improve their mechanical properties, especially the elongation, and sufficient results were obtained with an approximate ratio of 3/11/86.