Closed-Loop Recyclable Bio-Based Polyesters Featuring a Tricyclic Diglycolicaldehyde Xylose Diol toward High <i>T</i> _g and Excellent Gas Barrier Performance

Biobased degradable polyesters have emerged as a promising alternative to mitigate plastic pollution and reduce dependence on petroleum resources. However, the utilization of tricyclic rigid diols derived from biomass remains limited, which restricts the overall performance of degradable polyesters. In this study, a novel diglycolicaldehyde xylose (DGX) diol containing a rigid tricyclic structure, synthesized from D-xylose and glyoxylic acid hydrate, is reported. Both the single- and multiple-stereoisomer forms of DGX were polymerized with linear diacids of varying carbon chain lengths to produce biobased poly(xylosediethylene alkylenedicarboxylate)s (PXAs) and m-PXAs polyesters. The high rigidity of the single-regioisomer DGX conferred enhanced thermal properties to PXAs, with a 5% weight loss temperature (<i>T</i>_d,5%) reaching 372 °C and a glass transition temperature (<i>T</i>_g) of up to 93.8 °C. The structural regularity of the PXAs polymer backbone, combined with their higher molecular weights, resulted in a higher <i>T</i>_g relative to the m-PXAs analogues. Furthermore, the tricyclic unit endowed the polyesters with a superior gas barrier performance. Notably, the PXD film exhibited oxygen (O₂) and carbon dioxide (CO₂) barrier capabilities that were 3 and 7 times greater than those of polylactic acid (PLA), respectively. All amorphous polyesters allowed efficient recovery of DGX under mild conditions, with a yield of 93% achieved, and the recycled polymers displayed properties comparable to those of the virgin materials, thus demonstrating the potential for closed-loop recycling. This work presents a viable strategy for designing high-performance, sustainable biobased polyesters with end-of-life utility.