Bio-Based Pentamethylenediamine-Derived Semiaromatic Copolyamide: Controllable Synthesis and Discoloration Mechanism

The long-ignored discoloration behavior of polyamide during polymerization has a significant impact on its properties and applications. Here, we innovatively analyzed the discoloration behavior of pentamethylenediamine-derived bio-based copolyamide (PA5T/56) and proposed a possible discoloration mechanism. Pentamethylenediamine performed cyclization reactions at high temperature to generate piperidine, which was then combined with terephthalic acid to form dipiperidine terephthalate. After being oxidized, dipiperidine terephthalate was converted to terephthalic acid bis(2-carbonyl substituted piperidine), which was believed to be responsible for the discoloration of polyamide during polymerization. Moreover, it was demonstrated that the discoloration behavior led to poor spinnability and dyeability of ultrafine polyamide fibers. This work will help to optimize the polymerization process of pentamethylenediamine-derived polyamide and expand its applications in high-performance fibers and other fields.