Large-scale Fabrication of Less Entangled Polyamide by Direct Solid-state Polymerization and the Impact of Entanglement on Crystal Structure and Performance

Polyamide 66 (PA66) with less entangled structure, high crystallinity and excellent mechanical properties was fabricated in this work by direct solid-state polymerization (DSSP) method. The polymerization process and mechanism of DSSP were systematically investigated. Results demonstrate that DSSP is a transition process from salt crystal directly to polymer crystal, enabling the production of PA66 with a less entangled and highly crystalline structure. DSSP sample exhibits a crystallinity of 51.8% as tested by WAXD, and 59.7% when measured via DSC, surpassing the crystallinity of the majority of PA66 fibers. Furthermore, the sample achieves a maximum melting point of 271.7 °C. Correspondingly, mechanical properties and heat distortion temperature of DSSP sample are also improved. Therefore, this work enhances the in-depth understanding of polymerization mechanism of DSSP, and provides an efficient, scalable approach for fabricating polymers with less entanglement, high crystallinity, and exceptional performance characteristics.