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Curdlan, a β-1,3-glucan polysaccharide, produced by microorganisms, was used as a raw material to synthesize a completely substituted Curdlan mixed ester, Curdlan acetate propionate (CDAcPr). The degree of propionylation was changed (0.4–2.8), and the resulting thermal and crystal properties were analyzed using DSC and wide-angle X-ray diffraction (WAXD). Results showed that CDAcPr had a single Tgat all degrees of propionylation, indicating that the acyl groups were randomly distributed in its molecular chains rather than a physical blend of homoesters. Further, unlike typical mixed esters, CDAcPr also showed melting points ranging from 293 to 231 °C, with several samples showing multiple melting peaks. WAXD results suggested that CDAcPr underwent cocrystallization observed in certain copolymers, exhibiting isodimorphism. The crystal structure and melting point of CDAcPr could be controlled by changing the degree of propionylation. Such structural control greatly expanded the possibilities of biomass-based plastics derived from polysaccharides.

To establish a sustainable material production system and preserve the Earth’s environment, “biomass plastics” that are made from renewable biomass instead of petroleum and “biodegradable plastics” that are completely degraded into carbon dioxide and water by enzymes secreted by microorganisms in the environment are desirable products. This miniature review describes a series of studies on microbial polyesters and polysaccharide ester derivatives, including the synthesis of novel polymers, development of new processing techniques for high-performance films and fibers, elucidation of the relationship between structure and properties using synchrotron radiation, and control of the rate of enzymatic degradation.