Design of Biobased Polycondensates: Structural Regulation of Properties and Closed-Loop Recycling

Long-chain biobased polycondensates are of growing interest for their recyclability and property enhancement, yet combined studies linking their synthesis, structure–property relationships, and closed-loop recycling remain scarce. To this end, this article explores a novel approach in which polycondensates derived from renewable resources with phenyl ether defects in the backbone were developed, and their closed-loop recycling was achieved. Specifically, it focuses on the integration of a biosourced diol monomer (C22) containing a phenyl ether linkage in the middle with a renewable fatty acid-derived 1,16-dimethylhexadecanedioate (C16) to produce a long-chain polycondensate via melt transesterification. The relative positions of the two ether linkages in the phenyl ether at the polymer backbone were systematically varied from ortho (1,2) to meta (1,3) to para (1,4). The thermal properties, crystallization behaviors, and mechanical properties of these polymers can be regulated through systematic variation in the position of phenyl ether defects within the polymer backbone, as revealed by differential scanning calorimetry (DSC), wide and small-angle X-ray scattering, microscopic techniques, and tensile testing. Moreover, depending on the position of the ether linkage, it may be either incorporated into or excluded from the crystalline domains, thereby significantly influencing the long-range ordering of the polymers. Impressively, the ester linkages in the polymer backbone provided a handle for degrading the polymer using excess methanol and recovering the monomers. The monomers were recovered with high purity and yield (>90%). Preparation of fresh polymers from recovered monomers was achieved without significant loss of the original material properties, thereby enabling a sustainable, circular economy. Overall, this study presents the design of sustainable, biobased polycondensates that can be tailored in structure and properties and, at the same time, recycled in a closed-loop fashion.