Regulating Molecular Chain Entanglement to Enhance Spinnability: Optimizing <scp>PMIA</scp> Fiber Production Through Neutralizer Selection

ABSTRACT Synthesis of poly‐m‐phenylene isophthalamide (PMIA) solutions via polycondensation inherently generates HCl as a by‐product, adversely affecting polymer stability and necessitating neutralization. Introducing neutralizers adds water, a non‐solvent for PMIA, and cosolvent salts into the solution. Water induces curling of the polymer chains, reducing interchain entanglement and decreasing viscosity and elasticity of the solution. Adversely, cosolvent salts containing central ions with higher valence states and smaller ionic radii exhibit increased charge density and polarization capacity. It promotes more effective coordination bonding, forming a stronger entanglement network that affects the rheological properties of the spinning solution. This study systematically investigates the rheological behavior of PMIA solutions neutralized with different agents and characterize the structure and properties of fibers produced via the dry‐jet‐wet spinning. Results reveal that solutions neutralized with Li 2 CO 3 or CaCO 3 exhibit appropriate viscosity and relatively low levels of chain entanglement, which are conducive to enhanced spinnability. Moreover, fibers spun from these solutions display smooth surfaces and elliptical cross‐sections without noticeable defects or voids. Considering both economic viability and the superior mechanical properties of the fibers, CaCO 3 is the preferred neutralizer for PMIA solutions, resulting in fibers with high tensile strength (4.87 cN/dtex) due to increased crystallinity and molecular orientation.