Yasushi Osanai

Enzymatic transformation of aliphatic polyesters into cyclic oligomers using enzyme packed column under continuous flow of supercritical carbon dioxide with toluene

Abstract The enzymatic degradation of chemically synthesized typical biodegradable plastics, such as poly(R,S-3-hydroxybutanoate), poly(3-caprolactone) and poly(butylene adipate), into reactive cyclic oligomers under the continuous flow of supercritical or subcritical carbon dioxide (scCO2) with toluene through an enzyme column was studied with reference to chemical recycling. It was confirmed that all the tested polymers were quantitatively transformed into the corresponding cyclic oligomers by passage through the column packed with immobilized lipase from Candida antarctica (Novozym 435) at 40 8C under the continuous flow of scCO2 with some organic solvent. Compared to the pure organic solvents, by the addition of scCO2 as a mobile phase degradation of the polymer was significantly promoted with respect to the reaction time, temperature and polymer concentration for complete transformation of the polyesters into oligomers through the enzyme column. This phenomenon is ascribed to the high diffusivity, low viscosity and better mass-transfer properties of scCO2 as the reaction media. The degradation activity of the enzyme column was maintained for at least 6 months at 40 8C.

Enzymatic degradation of poly(R,S-3-hydroxybutanoate) to cyclic oligomers under continuous flow

The enzymatic degradation of chemically synthesized poly(R,S-3-hydroxybutanoate) (PHB) to a reactive cyclic oligomer under continuous flow using an enzyme column was studied and directed towards green chemical recycling. It was confirmed that atactic and syndiotactic PHBs were quantitatively transformed into the corresponding cyclic oligomer by passing through a column packed with immobilized lipase from Candida antarctica (Novozym 435) at 40 °C using toluene solution. The degradability of the polymer depended on the reaction conditions, such as flow rate and the polymer concentration. A higher flow rate and higher polymer concentration caused incomplete degradation of the polymer. The 40 °C-degradation was suitable for both rapid degradation of PHB and enzyme stability. The degradation activity of the enzyme column was maintained for at least two months at 40 °C.

Lipase‐Catalyzed Ring‐Opening Polymerization of β‐Butyrolactone: End‐Group Analysis of Poly(3‐hydroxybutanoate) Using Supercritical Fluid Chromatography

The ring-opening polymerization of (R,S)-β-butyrolactone (BL) in bulk was analyzed with respect to the polymer structure of the resulting poly[(R,S)-3-hydroxybutanoate)] [P(3HB)] by isolation of the pure form using preparative supercritical CO 2 fluid chromatography. It was confirmed that the four-membered BL was polymerized in bulk by lipase to yield the corresponding cyclic, hydroxy-and crotonate-terminated P(3EB)s. The relative ratios of the three types of polymers depended on the lipase concentration as well as on the monomer conversion. It was also confirmed that both cyclic and linear P(3HB) polymer species were subject to hydrolysis, and inter- and intramolecular transesterification by lipase to produce two series of polymers having linear and cyclic structures with higher and lower molecular weight. The formation of the cyclic P(3HB) is regarded as the characteristic feature of the lipase-catalyzed polymerization of BL.

Lipase‐Catalyzed Transformation of Unnatural‐Type Poly(3‐hydroxybutanoate) into Reactive Cyclic Oligomer

Unnatural-type syndiotactic and atactic poly[(R,S)-3-hydroxybutanoate]s [P(3HB)s] were enzymatically transformed into a reactive cyclic 3HB oligomer of molecular weight ca. 500 in an organic solvent, such as toluene, using immobilized lipase from Candida antarctica at 40°C for 24 h. It was confirmed that similar results were obtained for both syndiotactic and atactic P(3HB)s. On the other hand, the acidic degradation of these polymers using a protonic acid, such as p-toluenesulfonic acid, exclusively produced the linear 3HB oligomer instead of the cyclic oligomer. The formation of the cyclic oligomer was regarded as the characteristic feature of the lipase-catalyzed degradation in organic media. The cyclic oligomer obtained readily reacted with alcohol as a nucleophile, and using lipase, to produce the alkyl ester of the 3HB oligomer.

Phase-separation enhanced enzymatic degradation of atactic poly(R,S-3-hydroxybutyrate) in the blends with poly(methyl methacrylate)

The dependences of the phase structure and biodegradability on the thermal histories were investigated for amorphous atactic poly(R,S-3-hydroxybutyrate) (aPHB) in amorphous blends with atactic poly(methyl methacrylate) (PMMA).Poly(R-3-bydroxybutyrate)(PHB) depolymerase isolated from Ralstonia pickettii T1 was used as an enzyme. Pure aPHB in a rubbery state could not be degraded by PHB depolymerase. The results of DSC and TEM observations revealed that aPHB/PMMA blends were partially miscible with compositional heterogeneity. When the blends have a proper phase distribution of both the hydrolyzable rubbery phase and the depolymerase-adsorbable glassy phase, resulting from compositional heterogeneity, the enzymatic degradation of aPHB can be induced by blending with amorphous PMMA. Through the thermal treatment, the weight loss due to enzymatic degradation much increased for some blends.The reason is because such blends formed “micro-separated” structure, that is, the blends had “optimal” phase distributions consisting of enzyme-adsorbable PMMA-rich domains dispersed in the aPHB-rich matrix compositionally closer to pure aPHB. It was suggested that the aPHB component should be degraded faster in the aPHB/PMMA blends with compositional heterogeneity than in the miscible blends.

Thermal and infrared spectroscopic studies on hydrogen-bonding interaction of biodegradable poly(3-hydroxybutyrate)s with natural polyphenol catechinPresented at The First International Conference on Green & Sustainable Chemistry, Tokyo, Japan, March 13?15, 2003.

Thermal and infrared spectroscopic studies were performed on the hydrogen-bonding interaction in the blends of biodegradable atactic, highly syndiotactic and isotactic poly(3-hydroxybutyrate)s with catechin. From the analysis of Fourier-transform infrared spectra, it was found that the crystalline phase could greatly restrain the formation of inter-associated hydrogen-bonds. Moreover, the effect of the steric configuration on the formation of hydrogen-bonds was testified, and the results suggested that the higher tacticity benefited the formation of hydrogen-bonds, although its effect on the strength of hydrogen-bonds was small. The strong hydrogen-bonds between the two components in the blends promised their miscibility, which could be testified by differential scanning calorimetry measurements. All the poly(3-hydroxybutyrate)–catechin blends showed one glass transition temperature over the whole range of blend compositions and it increased rapidly with catechin content, indicating that poly(3-hydroxybutyrate)s and catechin are miscible in the amorphous phase.