Rational Design of Electrically Conductive Cross-Linked Polyimide–Polypyrrole with High Thermal Stability

The increasing focus on high-temperature conductive applications has led to a significant rise in the demand for electrically conductive polyimides (PIs). Nevertheless, current conductive PIs face challenges in simultaneously achieving high conductivity and thermal stability. To address this issue, in this work, a diamine monomer (6-POPDA) featuring a pendant pyrrole ring was synthesized and copolymerized with 4,4’-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) to produce poly(amic acid) (6-POPPAA). 6-POPPAA was ionized and then mixed with a pyrrole monomer and dopant to create a suspension, which underwent electrophoretic deposition. During this process, the 6-POPPAA film was electrodeposited, and simultaneously, the pendant pyrrole rings on the 6-POPPAA chains were electrochemically polymerized with the pyrrole monomers in the suspension to form polypyrrole (PPy). Consequently, the cross-linked 6-POPPAA–PPy film was obtained, which was then chemically imidized to yield the cross-linked 6-POPPI–PPy film. The incorporation of a long-range conjugated PPy structure endowed 6-POPPI–PPy with a high electrical conductivity of 6.32 S/cm. Furthermore, 6-POPPI–PPy exhibited remarkable thermal stability, with 5% and 10% weight loss temperatures (Td5% and Td10%) of 456 and 476 °C, respectively, attributed to the covalent cross-linking between the 6-POPPI and PPy molecular chains. 6-POPPI–PPy also demonstrated exceptional high-temperature conductivity retention and favorable mechanical properties. After annealing at 200 °C, 6-POPPI–PPy retained a conductivity of 5.45 S/cm with a high retention ratio of 86%, whereas pure PPy almost lost its conductivity. This study offers important theoretical guidance for designing high-performance conductive PIs for high-temperature conductive applications.