Intrinsic Colored Flexible meta-Aramid with Highly Stable Fluorescence Emission

In consideration of the rigid structure of meta-aramid (PMIA) and its difficulty in processing and dyeing, this work describes the preparation of two intrinsically chromogenic, high-performance aromatic polyamides (R-PMIA and Y-PMIA). 4,4′-Diaminodiphenyl ether was used to improve the flexibility of PMIA, while color was achieved by polymerizing diamine monomers containing chromogenic anthraquinone or acridine cores. The molecular structures of R-PMIA and Y-PMIA were confirmed by ¹H NMR spectra. The flexible films with a thickness of 20–40 μm were prepared by solution casting and dry-wet processing methods, and they had relatively smooth surfaces and showed ductile deformation characteristics in fracture. The flexibility of R-PMIA and Y-PMIA films had been improved compared with the original aramid, and the elongation at break was increased by 63.6% and 28.8%, respectively. Despite a certain degree of thermal stability and mechanical strength degradation, the initial thermal decomposition temperature of the films remained at 389 and 395 °C, and the tensile strength exceeded 95 MPa. XRD results showed that there was no crystallization, and the glass transition temperature of the films was lower than that of the original aramid, which was beneficial to improving the processability of aromatic polyamide. In terms of color characteristics, R-PMIA and Y-PMIA films presented purple-red and yellow, respectively, and had excellent color fastness. In addition, the films also exhibited fluorescence properties, with maximum emission wavelengths of 643.2 and 557.8 nm, which were almost unaffected by external factors such as chemicals and high temperatures.