Design, synthesis and properties of conductive crosslinked polyimide-polypyrrole with high thermal stability

Abstract

With the rapid advancement of high-temperature conductive technologies, electrically conductive polyimides (PIs) face a critical challenge in balancing high conductivity with excellent thermal stability. To address this limitation, this study proposes a molecular design strategy integrating covalent crosslinking and conjugated conductive networks. Based on this, a new diamine monomer (4-POPDA) containing pendant pyrrole rings was synthesized and polymerized with 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) to form poly(amic acid) (4-POPPAA). A suspension of ionized 4-POPPAA, pyrrole monomers, and dopant was electrophoretically deposited. During this process, the 4-POPPAA film was electrodeposited, and at the same time, the pendant pyrrole rings on the 4-POPPAA chains electrochemically polymerized with the pyrrole monomers in the suspension to form a covalently crosslinked polypyrrole (PPy) network. The obtained crosslinked 4-POPPAA-PPy film was then chemically imidized to form crosslinked 4-POPPI-PPy film. With the formation of long-range conjugated PPy network, the obtained 4-POPPI-PPy film presented a high electrical conductivity of 15.82 S/cm. Meanwhile, the 4-POPPI-PPy film showed high thermal properties with 5 % and 10 % weight loss temperatures (T_{d5 %} and T_d10 %) of 431 °C and 473 °C, respectively, owing to the covalent crosslinking formed between the 4-POPPI and PPy molecular chains. Furthermore, the crosslinked 4-POPPI-PPy film had excellent high-temperature conductivity retention and favorable mechanical properties. After annealing at 250 °C, the crosslinked 4-POPPI-PPy film still had a conductivity of 7.52 S/cm, while the pure PPy lost its conductivity. This work provides theoretical guidance for the preparation of high-performance conductive PIs for high-temperature conductive applications.