Intrinsically Colored Polyimide Films Prepared by Embedding Chromophores on the Polymer Backbones

A versatile strategy of preparing colored polyimide (PI) films is developed by embedding colored monomers on the backbones of colorless substrate polymers. Intrinsically colored PI films of four colors-red, yellow, blue, and purple-are prepared by introducing relative chromophores to the substrate PI that are synthesized from 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA)-two widely used monomers for colorless and transparent PI films. In addition, a series of orange and green PI films are prepared by simple mixing of the red, yellow, or blue PIs. The properties of these colored PI films are characterized, exhibiting good mechanical, thermal, and solubility properties, as well as different color and brightness depending on the amounts and types of chromophores. The optical properties of these films are determined by UV-vis spectroscopy and Commission Internationale de I'Eclairage (CIE) Lab. It is demonstrated that the introduction of even small amounts of chromophores can afford spectrally colored films while maintaining the original benign properties of the substrate PIs.