Interface‐Engineered Polyimide/Carbon Nanotube Nanocomposites via Poly(Amic Acid) Salt Functionalization for Enhanced Mechanical and Electrothermal Performance

Polyimide (PI) films are widely utilized in advanced engineering applications due to their excellent thermal stability, mechanical integrity, and electrical insulation. Despite these advantages, their intrinsic brittleness limits broader structural implementation. In this work, carbon nanotubes (CNTs) were non‐covalently functionalized using poly(amic acid) salt (PAS), a precursor polymer structurally similar to PI, to enhance filler dispersion and interfacial compatibility. The PAS modification markedly improved CNTs distribution within the PI matrix, leading to strengthened interfacial interactions and more efficient stress transfer. Mechanical testing showed that neat PI exhibited a tensile strength of 128.38 MPa, whereas incorporation of 0.5 wt% PAS‐CNT the increased the tensile strength to 214.44 MPa, corresponding to a 67.03% enhancement. The tensile modulus simultaneously increased from 4.41 to 7.96 GPa (80.50% improvement). Specifically, the PAS‐CNT/PI nanocomposites reached a conductivity of 168.55 S/m was achieved, which is approximately 7.86 times higher than that of pristine CNT/PI nanocomposites (21.43 S/m) at the same filler content (5 wt%). The improved conductivity enabled rapid and stable electrothermal heating under applied voltage. These results demonstrate that PAS‐assisted non‐covalent functionalization is an effective strategy for improving the dispersion and multifunctional performance of PI/CNT nanocomposites for electrothermal film applications.