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

Copolymerization\nwith aliphatic acid was an effective approach\nto improve the processability of high-temperature nylon 5T by designing\na polymer molecular structure. In this study, nylon 5T and nylon 56\nsalts were prepared via the reaction crystallization method with a\nyield of 96%. The thermodynamics properties, dissolution behaviors,\nand single-crystal structure of nylon salts were investigated. Hirshfeld\nsurface analysis proved that intermolecular hydrogen bonds existed\nin both nylon 5T salt crystals and nylon 56 salt crystals, which were\ntightly embedded to give a relatively stable crystal structure of\nthe nylon salts. The solid-state copolycondensation reaction was applied\nto produce nylon 5<i>T</i>/56 copolymers. <i>In situ</i> DRIFT-IR showed that the hydrogen bond interactions between the\npolyamide chains in nylon 5T were largely weakened after the addition\nof the nylon 56 segment. The flexible nylon 56 segment greatly facilitated\nthe conformational change of the rigid nylon 5T chain. Chain defects\ninvolving gauche conformations were also observed, indicating the\nexistence of an amorphous phase in the nylon 5<i>T</i>/56\ncopolymer. Finally, the thermal and thermodynamic properties of nylon\n5<i>T</i>/56 copolymer were studied through DSC and TGA.\nThe 5T part was found to play an important role in enhancing the nonisothermal\ncrystallization and the high thermal properties of nylon 5<i>T</i>/56 as its rigid benzene structure.