Mutual relation between microstructure and properties of bacterial copolyesters

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Poly [(R)-3-hydroxybutyrate] [PHB] and its copolymers, which are produced from renewable resources by bacterial fermentation, attract widespread interest as biodegradable thermoplastics. In this project, mutual relation between microstructure and properties of bacterial copolyesters were analyzed. Properties of Polymeric materials are correlated with structures of diverse levels from atomic to macroscopic scales, this project was directed toward deep analysis of a copolyester, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV), rather than shallow one of various coplyesters. We have achieved the following results.1. A speculer structural transition was found at ca. 10 mol% HV for PHB-HV with narrow chemical composition distribution.2. For PHB-HV with bimodal chemical composition distribution, the phase structure changes from perfect cocrystallization of all the PHB-HV chains, via crystallization of the PHB-HV with high HV content, to phase segregation preceding crystallization with the increase of the difference in the peak positions in composition distribution and/or the decrease of the crystallization temperature. Coincidentally various properties of PHB-HV remarkably changes.3. Through in situ observation of crystallization of PHB-HV with bimodal composition distribution by FTIR microscopy, the formation mechanism of the phases described above was demonstrated.