Presentations

Recently, polythioester has attracted attention due to their interesting properties, such as high melting point and heat stability. Synthesis of high molecular weight poly(thio-oxyester) using an enzyme was studied. First, 6-mercapto-1-hexanol and dimethyl sebacate were reacted in n-nonane using lipase CA to produce cyclic(thio-oxyester). A poly(thio-oxyester) having an Mw of about 120,000 was prepared by the ring-opening polymerization of cyclic(thio-oxyester)using lipase CA. A higher melting point was observed compared with the corresponding poly(oxyester). The rate-determining step of the polymerization was determined to be the nucleophilic attack by the thiol, which differs from the corresponding enzymatic polymerization reactions.

Seven-membered cyclic tetramethylene carbonate was synthesized by the condensation of butane-1,4-diol and diphenyl carbonate in a toluene solution using immobilized lipase from Candida antarctica(lipase CA) as an environmentally benign process. The cyclic tetramethylene carbonate was readily polymerized by lipase CA in bulk to produce poly(tetramethylene carbonate) (PTeMC) with a molecular weight of 103,000. The molecular weight of PTeMC prepared by the ring-opening polymerization of cyclic carbonate was significantly higher than that produced by the direct polycondensation of butane-1,4-diol and diethyl carbonate using lipase CA. It was also found that PTeMC was amorphous as determined by DSC, and the contact angle of the surface of PTeMC was 83ｏ(±1.3ｏ).

Chemical recycling of poly (butylene succinate) (PBS) was studied using a lipase with respect to the ring-size of the oligomer. It was found that PBS was degraded in a dilute toluene solution using lipase CA to produce cyclic oligomers mainly consisting of dimer and trimer. By the ring-opening polymerization of isolated cyclic BS dimer by lipase, PBS with an Mw of 170,000 was produced. On the other hand, PBS with an Mw of 130,000 was produced from isolated cyclic trimer. That is, cyclic dimer produced a higher molecular weight polyester than from cyclic trimer by the ring-opening polymerization. By degradation of PBS using lipase CA, cyclic dimer was obtained in a maximum yield of 70%.

The greening of chemistry in the field of polymer science may include the design and synthesis of chemically recyclable and biodegradable plastics using renewable resources, and the application of environmentally benign catalysts. In this report, enzyme-catalyzed synthesis and degradation of diol-diacid type plastics, such as poly(butylene succinate) (PBS), poly(butylene adipate) (PBA) and poly(hexylene fumarate) (PHF), were studied with respect to the establishment of sustainable polymer production and chemical recycling system. As an application of this enzymatic chemical recycling of PBS, the selective chemical recycling of poly(lactic acid) (PLLA)-based polymer blend, PLLA/PBS, using an enzyme and a clay catalyst was reported.