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Aliphatic polycarbonates (APCs) have become an essential packaging material because of their renewability, biodegradability, and biocompatibility. In this study, a series of high molecular weights APCs have been successfully synthesized using dimethyl carbonate (DMC) and different lengths of aliphatic diols with even carbon (n-CH2 = 4–12) via melt polymerization. Thermal properties, isothermal crystallization behavior, crystal structure, and scale of microstructure of APCs indicated that the flexibility and crystallization of molecular chains gradually increased with the increasing number of methylene groups of repeating units. However, due to the rigidity of ester group was higher than methylene group, and crystallization could increase the rigidity of chain segments, yielding strength and Young's modulus of APCs decreased first and then gradually increased with the increasing number of methylene groups in the repeating units. Furthermore, the scale of microstructure indicated that Brill transition increased the distance between intermolecular chains. Therefore, although the trans-gauche coexistence chain conformation simultaneously decreased the rigidity and crystallization of chain segments, barrier property of poly(octamethylene carbonate) with Brill transition was similar to long-chain APCs because of the lengthened diffusion path. The analytical mechanism of structure-performance relationship from the viewpoint of molecular interactions and chain structure will provide an entirely new thought for developing new barrier materials. [ABSTRACT FROM AUTHOR]