Biodegradable Poly(oxamide ester)s from Adipic Acid and Amino Alcohols with Different Chain Lengths: Synthesis, Characterization, and Properties

Poly(amide ester)s (PAEs) have attracted substantial academic interest as efficient and versatile biodegradable materials. However, conventional linear aliphatic PAEs often have low melting temperatures, which limit their suitability for production and processing, restricting their applications. Among PAEs, poly(oxamide ester)s (POAEs) feature a trans-aligned o-dicarbonyl structure in their molecular chains, allowing for high-density, adjacent double hydrogen bonds that enhance their melting temperature. In this study, we synthesized structurally regular aliphatic POAEs with high melting temperatures using an innovative two-step method. Dimethyl oxalate, commonly used in ethylene glycol production from coal, was reacted with amino alcohols (NH2-(CH2)n–OH, n = 2–6) of varying methylene chain lengths, producing a series of oxamidodiol intermediates (nOn). These intermediates were then subjected to melt polycondensation with adipic acid to yield the target POAEs (PnOn6). The reaction kinetics of PnOn6 during vacuum melting polymerization were analyzed, allowing for optimization of polymerization temperature and time, resulting in a series of POAEs with melting temperatures ranging from 142 to 168 °C, maximum tensile strengths of 31 MPa, and fracture strains of 404%. Notably, P3O36 and P4O46 demonstrated excellent biodegradability, with weight losses exceeding 50% in proteinase K solution after 20 days. The successful synthesis of the PnOn6 series extends the potential applications of biodegradable materials.