Tailored performance optimization of p-aramid copolymer fibers: From strength to thermo-chemical durability

aramid ( p -aramid) fibers, traditionally used in bulletproof vests because of their exceptional strength and modulus, are now widely utilized in optical cables and the aerospace industry. This growing demand driven by advanced applications requires precise performance grading to meet diverse operational requirements. This study proposes a rational copolymerization strategy for tailoring the properties of p -aramid copolymer ( co - p -aramid) fibers by adjusting the ratio of 3,4′-oxydianiline (3,4′-ODA) and 4,4′-oxydianiline (4,4′-ODA). While 3,4′-ODA enhances mechanical strength, 4,4′-ODA improves thermo-chemical stability. For high-strength applications, co - p -aramid fibers synthesized with 3,4′-ODA as the sole comonomer achieve a tensile modulus and tensile strength of 80.4 and 3.1 GPa, respectively. For superior thermo-chemical resistance, fibers with a 3,4′-ODA:4,4′-ODA molar ratio of 2:8 exhibit the highest stability, with a decomposition temperature of 484.1 °C, which is 25.7 °C higher than that of the sole 3,4′-ODA-based fiber. Further, these fibers demonstrate strong chemical durability, retaining 42 % and 98 % of their tensile strength and modulus, respectively, after 24 h in 60 wt% nitric acid, whereas the latter retains only 15 % and 61 %. These findings confirm that molecular design using positional isomers effectively fine-tunes the performance of co - p -aramid fibers, establishing a foundation for developing customized high-performance fibers. • ODA positional isomers (3,4′-ODA and 4,4′-ODA) are incorporated as comonomer for co- p -aramid fiber design. • We clarify how positional isomers govern the development of fiber microstructure. • Extended chain induced by 3,4′-ODA results in high mechanical performance. • Rigid and dense chain from 4,4′-ODA enhances thermal and chemical durability. • Molecular-level control enables systematic tuning of properties for target applications.