Intrinsic Colored\nFlexible <i>meta</i>-Aramid\nwith Highly Stable Fluorescence Emission

In consideration of the rigid structure of <i>meta</i>-aramid (PMIA) and its difficulty in processing and dyeing, this\nwork describes the preparation of two intrinsically chromogenic, high-performance\naromatic polyamides (R-PMIA and Y-PMIA). 4,4′-Diaminodiphenyl\nether was used to improve the flexibility of PMIA, while color was\nachieved by polymerizing diamine monomers containing chromogenic anthraquinone\nor acridine cores. The molecular structures of R-PMIA and Y-PMIA were\nconfirmed by <sup>1</sup>H NMR spectra. The flexible films with a\nthickness of 20–40 μm were prepared by solution casting\nand dry-wet processing methods, and they had relatively smooth surfaces\nand showed ductile deformation characteristics in fracture. The flexibility\nof R-PMIA and Y-PMIA films had been improved compared with the original\naramid, and the elongation at break was increased by 63.6% and 28.8%,\nrespectively. Despite a certain degree of thermal stability and mechanical\nstrength degradation, the initial thermal decomposition temperature\nof the films remained at 389 and 395 °C, and the tensile strength\nexceeded 95 MPa. XRD results showed that there was no crystallization,\nand the glass transition temperature of the films was lower than that\nof the original aramid, which was beneficial to improving the processability\nof aromatic polyamide. In terms of color characteristics, R-PMIA and\nY-PMIA films presented purple-red and yellow, respectively, and had\nexcellent color fastness. In addition, the films also exhibited fluorescence\nproperties, with maximum emission wavelengths of 643.2 and 557.8 nm,\nwhich were almost unaffected by external factors such as chemicals\nand high temperatures.