The Ester/Amide Exchange Reaction in the Melt Polycondensation of Alternating Poly(Ester Amide)s: Mechanism and Evolution

Poly(ester amide)s (PEAs) have emerged as a promising class of high-performance biodegradable materials, garnering significant research interest. However, achieving a strictly alternating structure in PEAs remains challenging due to ester–amide exchange reactions occurring during bulk polymerization. In this study, the mechanism underlying these exchange reactions was investigated by analyzing carbonyl group transformations during the polycondensation of N,N-bis (3-hydroxypropyl) adipamide (363 diol) and adipic acid. Thermodynamic and kinetic studies of model reactions confirmed the inevitability of the ester/amide exchange. To address this, a reduced-pressure esterification strategy was proposed, effectively enhancing the structural regularity of poly(ester amide)s and increasing their crystallization enthalpy from 11 to 26 J/g. This study provides a flexible and efficient approach to the production of high-quality poly(ester amide)s.