Structure of Bio-based Polyamide 5654 Alternating Copolymer: Insights from Hydrogen Bond, Conformation and α-γ Brill Transition

Currently, the copolymer modification of PA56 mainly focuses on random copolymerization with other α-crystal form polyamides. In contrast, research on the structure and properties of PA54 remains insufficient, and its application is significantly limited by poor thermal stability. In this study, PA5654 alternating copolymer was prepared, and the hydrogen bond structure, molecular chain conformation, and α-γ Brill transition were investigated. Interestingly, after undergoing the Brill transition, PA5654 can form two crystal forms (γ and α). Although the underlying degradation mechanism remains unchanged, the PA5654 copolymer significantly suppresses the amide-bond scission observed in PA54. Compared with PA54, its initial decomposition temperature ( T 5% ) and maximum decomposition temperature ( T max ) increased by 19 °C and 71 °C, respectively, indicating that its thermal stability has been effectively improved.