Copolymerization of Bio‐Based Itaconic Acid–Pentanediamine Salt With Polyamide 6: Simultaneous Achievement of High Toughness and Low Oligomer Content

Improving the toughness and reducing the oligomer content of Polyamide 6 through a green and sustainable bio‐based modification strategy is of great significance for expanding its application potential. In this study, bio‐based itaconic acid pentanediamine salt (IPA) was copolymerized with ε‐caprolactam to prepare a bio‐based copolyamide (PA6‐IPA) containing pyrrolidone rings. The regulatory effects of IPA content on the oligomer content, thermal behavior, rheological properties, and mechanical properties of PA6‐IPA were systematically investigated. The successful synthesis of PA6‐IPA was confirmed by 1 H NMR and FT‐IR. The results showed that with the increase of IPA content, the oligomer content of PA6‐IPA decreased from 8.68% to 2.76%, the crystallinity crystallization temperature decreased significantly, and the relative content of crystal forms was regulated. In addition, PA6‐IPA 20 achieved an elongation at break of 382.5% and a tensile strength of 58 MPa, realizing excellent toughness enhancement while maintaining the original strength. This can be attributed to the addition of IPA, which disrupts the regularity of the chain segments, increases the amorphous region of the copolyamide, and enhances the mobility of the molecular chains. This study provides a feasible strategy for developing eco‐friendly, high‐performance bio‐based polyamides with balanced processability and mechanical properties.