From rigidity to flexibility: High-strength PMIA fibers with aromatic ether structures

Meta aromatic polyamide (PMIA) has high rigidity and low flexibility due to the rigid molecular structure and highly oriented hydrogen bonding interactions, which will make the stress concentration and damage of PMIA by force. It is necessary to improve flexibility while maintaining mechanical strength. The influence of different aromatic ether structure on properties of PMIA and the evolution mechanism of molecular chain conformation in flexible PMIA fibers during the drawing process are not clear. This work obtained two flexible PMIA fibers (PMAB-PMIA and ODA-PMIA) by introducing 1,3-bis (4-aminophenoxy) benzene (PMAB) and 4,4′-diaminodiphenyl ether (ODA) into molecular chain. The properties of PMIA with different aromatic ether structures and microscale analysis during drawing were explored. The flexible PMIA maintained excellent mechanical properties, thermal stability, and flame retardancy. The tensile strength of pristine PMIA, PMAB-PMIA and ODA-PMIA was 2.68, 2.55 and 2.64 cN/dtex, respectively, meaning that flexible PMIA fibers kept high tensile strength. Compared with pristine PMIA, the elongation at break of PMAB-PMIA and ODA-PMIA increased by 30.1 % and 16.4 %. Their maximum number of twists also increased from 177 to 237 and 258 twists/10 cm. The increased elongation at break and torsional resistance proved that flexibility of modified PMIA elevated. The molecular dynamics (MD) simulations indicated that the molecular chains of aromatic-ether PMIA had more folded conformations, thus offering superior flexibility and stress dissipation capabilities at microstructural level. This work systematically explored high-strength and flexible PMIA fibers based on aromatic ether, which is expected to guide the material design of future functional fibers.