Stressor-matched co-monomer design: a structure-driven framework for para-aramid thin films targeting industry-specific extreme environments

Para-aramid thin films face distinct environmental stressors depending on their application, yet conventional compositional optimization often yields inconsistent stability. This work proposes a structure-driven, stressor-matched co-monomer design strategy for para-aramid films by incorporating three functionally distinct co-monomers into the backbone: 4,4′-bis(4-aminophenoxy)biphenyl (BABP) for chain rigidity, 4,4′-(piperazine-1,4-diyl)dianiline (PIPE) for metal interaction, and 6-(4-aminophenoxy)pyridin-3-amine (APA) for photostability. The resulting copolymers (BABP-ARP, PIPE-ARP, and APA-ARP) were paired with their dominant targeted stressors: thermal shock cycling (250 °C ↔ − 60 °C), metal-ion exposure (FeCl3, CuCl2, ZnCl2), and UV-A photo-aging, respectively. While baseline thermal decomposition temperatures (Td5) remained comparable (483–489 °C), each system exhibited a unique response mechanism modulated by co-monomer content. After thermal cycling, BABP-ARP films retained their mechanical and structural integrity, with superior retention at higher BABP content (90 mol%). PIPE-ARP films (20 mol%) exhibited distinct metal uptake. Specifically, XPS analysis revealed a reduction in N 1s binding energy and counter-ion exchange, indicating electrostatic polarization rather than dative coordination. For APA-ARP, higher APA content (60 mol%) significantly improved mechanical retention against UV-induced degradation. These findings demonstrate that co-monomer architecture defines the dominant degradation-resistance mechanism, while its content modulates the response strength, providing a framework for designing task-specific aramid films for extreme environments.