Colorless polyimides (CPIs) with outstanding mechanical properties are essential materials in the production of flexible display panels, foldable windows, and even spacecraft cockpits. This paper specifically elaborates that the Morkit unit, and azo and nitro chromophores are important factors contributing to yellow PI, together with the well-known charge transfer complex (CTC) theory. Three diamine monomers, two anhydrides monomers, and three blockers were used to inhibit chromophores formation and, thus, obtain CPI films. The cut-off wavelength was blue-shifts to 334 nm and the transmittance is improved to 98.9% in the UV–vis range. Mechanical and thermal properties of the CPI films are not reduced through coupling effects of the blockers. Therefore, the inhibition method of the Morkit units and chromophore groups is a promising process for preparing CPIs to be used as flexible display materials.

Polymerized ionic liquids (PILs), especially N + -based PILs have been extensively studied as multifunctional materials. However, it remains challenging to synthesize O + -based PILs due to the fleeting characteristics of oxonium salts. Here, we describe a general method in obtaining oxonium PILs through post-polymerization treatment of oxy-polymers with concentrated sulfuric acid. The formation of O + -PILs induces dissolution of most oxygen-containing polymers, thus offering a novel strategy to recover carbon fibers (CFs) at ambient conditions from widely used epoxy thermosets characterized by insolubility and infusion. The recovered CFs show improved crystalline structure and enhanced strength than the virgin ones. The discovery of oxonium PIL is expected to significantly extend the research scope of traditional imidazolium-based PIL as oxygen-containing organic chemicals are far more common than nitrogen-containing compounds.