Synthesis and characterization of trace aromatic copolyamide 6 with tunable mechanical and viscoelastic behavior

Bis(6‐aminohexyl) terephthalamide/adipic acid (BAHT‐AA) was chosen to be used as a comonomer to develop a novel polyamide 6 (PA6) with the trace‐content aromatic structure. A series of polyamide 6 copolymers (coPA6) with trace BAHT‐AA loading were synthesized to yield the modified copolyamides with multiple interactions of hydrogen bonding and π‐π stacking on the PA6 backbone. It was proved that the thermal stability and mechanical properties of coPA6 were significantly enhanced because of the introduction of the trace BAHT‐AA segment. More importantly, adding a trace (1, 2, and 4 mole%) of BAHT‐AA could effectively increase the network structure and highly decrease the free volume fraction in the polymer system that is proved by the relaxation behavior and melt viscoelastic behavior. The results showed that the integrated performances of coPA6 were better than that of pure PA6, which was highly correlated with the aforementioned multiple interactions. For example, outstanding tensile strength (73.0 vs. 56.8 MPa), and modulus (1167 vs. 929 MPa), and so on. This work provided the traditional PA6 with the modification of outstanding mechanical and thermal performances, thus expanding its application for the plastics and textile industries. The synergistic effect of hydrogen bonding network, π‐π stacking, and free volume in the PA6 realizes tunable mechanical and viscoelastic behavior.