| Research Abstract |
It has been revealed that the hydrolase enzyme promoted the polymerization of versatile types of monomer forming polyesters and polycarbonates. One of the advantages of using a hydrolase enzyme for polymer production is the reversible reaction between polymerization and depolymerization. This study covers the enzyme-catalyzed polymerization and chemical recycling of biodegradable aliphatic polyesters and polycarbonates particularly highlighted for establishing green polymer chemistry. It was found that substrate specificity for the monomers was significantly influenced by the hydrolase enzyme origin. That is, four-membered lactones were readily polymerized by PHB depolymerase. On the other hand, medium and large-membered lactones were readily polymerized by lipase. Typical biodegradable polyesters, such as polycaprolactone (PCL), poly (3-hydroxyalkannoate) (PHA), polylactate (PLA), poly (alkylene alkanedioate) and poly (trimethylene carbonate), were depolymerized into the corresponding cyclic oligomers by using the immobilized lipase in an organic solvent containing a small amount of water. The obtained oligomer having a molecular weight of a few hundreds could be polymerized both by the lipase and conventional chemical catalyst. Supercritical carbon dioxide was also an adequate reaction medium for the lipase-catalyzed depolymerization of such a polyester into the repolymerizable cyclic oligomer as an organic solvent-free system. The continuous enzymatic degradation of aliphatic polyesters into cyclic oligomers was carried out using an immobilized lipase column in an organic solvent. PHA, PCL and poly (butylene adipate) were readily depolymerized into the corresponding cyclic oligomers by passage through the enzyme column packed with immobilized lipase using a toluene solution at 40℃. These results imply that even in the polymer industry, a sustainable polymer production system will be realized using biocatalysts.
|
