The enzymatic degradation and polymerization using an enzyme were carried out with respect to the establishment of a sustainable chemical recycling system for poly(epsilon-caprolactone) (PCL) which is a typical biodegradable synthetic plastic. The enzymatic transformation of PCL having an Mn of 110,000 using Candida antarctica lipase (lipase CA) in water-containing toluene at 40 degrees C afforded the corresponding cyclic dicaprolactone (DCL, 1,8-dioxacyclotetradecane-2,9-dione) in a yield of up to 97%. Thus the obtained DCL readily polymerized again using both the fresh and recovered lipase CAs.

High-molecular-weight polyricinoleate, with an M(w) of 100,600, was enzymatically prepared by the polycondensation of methylricinoleate using immobilized lipase from Pseudomonas cepacia (IM-PC) in bulk in the presence of 4 A molecular sieves at 80 degrees C for 7 d. Polyricinoleate was a viscous liquid at room temperature with a glass transition temperature (T(g)) of -74.8 degrees C, showed no crystallinity and was biodegraded by activated sludge. Polyricinoleate was readily cured using a dicumyl peroxide at 170 degrees C for 30 min to produce a chloroform insoluble crosslinked polyricinoleate with a hardness of 50A using durometer A.

Cover: Ricinoleic acid is obtained from the bean oil of naturally abundant castor plant. High‐molecular weight polyricinoleate was enzymatically prepared by the polycondensation of methyl ricinoleate using a lipase. It showed a good low temperature flexibility and biodegradability. It is expected to be used as a biodegradable and biobased elastomer. Further details can be found in the article by H. Ebata, K. Toshima, and S. Matsumura* on page 798.

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A novel bio-based thermosetting elastomer was prepared by the lipase-catalyzed polymerization of methyl ricinoleate with subsequent vulcanization. Some mechanical properties of the cured carbon black-filled polyricinoleate compounds were evaluated as a thermosetting elastomer. It was found that the carbon black-filled polyricinoleate compounds were readily cured by sulfur curatives to produce a thermosetting elastomer that formed a rubber-like sheet with a smooth and non-sticky surface. The curing behaviors and mechanical properties were dependent on both the molecular weight of the polyricinoleate and the amount of the sulfur curatives. Cured compounds consisting of polyricinoleate with a molecular weight of 100,800 showed good mechanical properties, such as a hardness of 48 A based on the durometer A measurements, a tensile strength at break of 6.91 MPa and an elongation at break of 350%.