Polyamide membranes with structural homogeneity regulated by alkyl chain engineering for precise molecular sieving

Abstract Precise sieving of structurally similar solutes in organic solvents is crucial for chemical industries such as pharmaceutical synthesis and petroleum refining. However, it remains technically challenging due to their similar physicochemical properties. Achieving this with organic solvent nanofiltration (OSN) requires membranes with narrow pore‐size distribution and tailored surface chemistry. Herein, we report an additive‐free strategy to prepare ultrathin, structurally homogeneous polyamide (PA) nanofilms via alkyl chain engineering during interfacial polymerization (IP). Alkyl chains synergistically regulate the diffusion kinetics and the reaction process: they enable rapid, uniform amine supply while introducing steric hindrance that moderates polycondensation. This dual regulation yields a structurally homogeneous PA layer with sub‐nanometer pores. The optimized membrane shows a sharp rejection curve and effectively separates antibiotics, demonstrating promise for pharmaceutical purification. This work advances the understanding of diffusion‐reaction synergy in IP and offers a facile strategy for precision separation membranes.