Synthesis of Bio-based High-Temperature Nylon 5<i>T</i>/56 via Solid-State Copolycondensation Reaction

Copolymerization with aliphatic acid was an effective approach to improve the processability of high-temperature nylon 5T by designing a polymer molecular structure. In this study, nylon 5T and nylon 56 salts were prepared via the reaction crystallization method with a yield of 96%. The thermodynamics properties, dissolution behaviors, and single-crystal structure of nylon salts were investigated. Hirshfeld surface analysis proved that intermolecular hydrogen bonds existed in both nylon 5T salt crystals and nylon 56 salt crystals, which were tightly embedded to give a relatively stable crystal structure of the nylon salts. The solid-state copolycondensation reaction was applied to produce nylon 5T/56 copolymers. In situ DRIFT-IR showed that the hydrogen bond interactions between the polyamide chains in nylon 5T were largely weakened after the addition of the nylon 56 segment. The flexible nylon 56 segment greatly facilitated the conformational change of the rigid nylon 5T chain. Chain defects involving gauche conformations were also observed, indicating the existence of an amorphous phase in the nylon 5T/56 copolymer. Finally, the thermal and thermodynamic properties of nylon 5T/56 copolymer were studied through DSC and TGA. The 5T part was found to play an important role in enhancing the nonisothermal crystallization and the high thermal properties of nylon 5T/56 as its rigid benzene structure.