Bio-Based Pentylenediamine Monomer-Based Chemical–Physical Change Mechanism of Thermo-Oxidative Aging of Long-Carbon-Chain Nylon

Bioengineered (enzyme-enabled) glutarimide-based polyamides have garnered increasing attention due to their renewable monomer availability, low cost, and high performance. However, their physicochemical aging behavior and the underlying mechanisms under realistic thermo-oxidative conditions remain insufficiently elucidated. In this work, we synthesized bio-based PA514 via melt copolymerization of pentamethylenediamine with tetradecanedioic acid and investigated its thermo-oxidative aging behavior and mechanisms under practical service conditions. Early during thermo-oxidative exposure, physical aging manifested as lamellar thickening predominates, resulting in increased yield strength and reduced elongation at break. With prolonged aging, chemical degradation processes─principally amide bond scission followed by pentamethylenediamine cyclization─reduce the number-average molecular weight and entanglement density, concomitant with a γ–α crystalline phase transition. These findings clarify the coupled physical and chemical aging pathway of bio-based PA514 and provide a mechanistic basis for predicting performance decay and optimizing processing and composite application strategies for pentamethylenediamine monomer-based polyamides.