Two-photon polymerization of all-aromatic polyimides as precursors for conductive carbonaceous three-dimensional structures

Polyimides are a class of high-performance engineering polymers that are traditionally manufactured in two-dimensional form factors. Recently, polyimides have emerged as three-dimensional (3D) printable carbon precursors compatible with various additive manufacturing modalities with feature sizes in the hundreds of micrometers scale. Aromatic polyimide pyrolysis yields conductive carbonaceous structures, enabling potential applications in microelectronics, semiconductors and energy storage. Polyimides exhibit desirable molecular ordering due to intermolecular and intramolecular charge transfer complexes, resulting in ordered graphitic structures after pyrolysis. This paper describes the 3D fabrication of a polyimide polysalt precursor with micrometer resolution via a two-photon polymerization process. Imidization and pyrolysis of the printed polyimide polysalt precursors yielded conductive carbon with conductivity values of 7.5 × 10¹ S m⁻¹ and 1.4 × 10² S m⁻¹ after pyrolysis at 1000 °C and 1600°C, respectively. An overall increase in conductivity with an increase in carbonization temperature indicated enhanced graphitic carbon order. Raman spectroscopy and TEM confirmed pronounced graphitic carbon order with higher carbonization temperature.