Intrinsically Black Polyimide with Retained Insulation and Thermal Properties: A Black Anthraquinone Derivative Capable of Linear Copolymerization

Black polyimide (BPI) is increasingly in demand for the development of photoelectric devices in place of yellow transparent polyimide, but BPI doped with carbon black shows serious insulation and mechanical performance deficiencies due to pinholes and uneven dispersion. Intrinsically BPI has thus attracted increasing interest in science and industry. Anthraquinone derivatives have an ample high molar extinction coefficient (ε), and appending as many auxochromes (−OH and −NH2) as possible on the anthraquinone skeleton can extend its light absorption range, thereby achieving complete UV–visible light absorption. However, the greatest obstacle to its application in BPI is retaining the monomer bifunctionality to avoid gel formation. In this work, a linearly polymerizable anthraquinone derivative, 2,4,5,7-tetraamino-1,8-dihydroxyanthracene-9,10-dione (4NADA), has been developed. Structural analysis of this monomer bearing multiple active groups by 1H NMR, Fourier-transform infrared, and theoretical calculations has demonstrated that the auxochrome groups show different nucleophilic activities owing to the formation of intramolecular hydrogen bonds, such that only p-amino groups (2- and 7-positions) can participate in the polymerization reaction. Subsequently, 4NADA was copolymerized into a Kapton-type polyimide. We found that low-level introduction of 4NADA (4%) afforded a spectrally BPI film that maintained the electrical insulation and heat resistance properties of polyimide. This method, equivalent to embedding a black monomer in polyimide chains, has merits of economy, universality, process consistency, ready accessibility, and superior performance.