Development of Novel Biodegradable Aliphatic Polyesters Prepared by Catalysts Containing Metals

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Poly (L-1actic acid), namely poly (L-lactide) [poly (L-LA)] has such advantages as good biocompatibility and mechanical properties. However, the major problems of poly (L-LA) are its brittleness and low biodegradability. Therefore, in this work, to improve these disadvantages of poly (L-LA), but keeping its advantages, we have prepared novel biodegradable aliphatic polyesters. The following significant results were obtainedImprovement of biodegradability of poly (L-LA) by introducing depsipetide (DP) units ; The enzymatic degradation of poly (L-LA) was much improved by copolymerizing DP monomer (DPs were synthsized from various amino asids and hydoxy acid derivatives). Furthermore, it was found that the biodegradability was most improved by using DP monmers prepared from L-isomers of amino asids.Improvement of brittleness of poly (L-LA) chains ; The introduction of caprolactone (CL) or its derivative (4-alkylated caprolactone) units into poly (L-LA) chains resulted in a greater improvement of the brittleness of poly (L-LA). And this enabled us to regulate the degradability of copolymers.The above results rendered us to prepare DP/CL/L-LA terpolymers. The terpolymer with composition ratio about 5/20/75 was found to be the best polymer judging by the balance of biodegradability and properties.For many applications of biodegradable polymers, functionalizations of these polymers are very important. We have therefore prepared L-LA copolymers having various **nctinal groups. For example, CL/L-LA copolymers with hydroxy group was found to be highly biodegradable compared with poly (L-LA). Further, we have synthesized the copolymers with multifunctional groups (double bond/epoxy/diol) by transforming the reactive double bond of polymers into these functional groups. Finally, we have succeeded in developing cross-linked hydrogel polymers by chemical modification of these groups.