Programming Interfacial Function through Alternating Sequence in Amphiphilic Copolymers

Control over monomer sequence in synthetic polymers remains a fundamental challenge, particularly for amphiphilic systems where spatial organization governs interfacial function. While recent advances have enabled alternating copolymer formation in select vinyl systems, translation of these strategies to functional amphiphilic polymers has remained largely unexplored. Here, we report a transformable bulky-monomer strategy that extends alternating copolymerization to methacrylamide-acrylate systems and enables the synthesis of cationic alternating copolymers with well-defined amphiphilic sequences. Post-polymerization modification affords polymers in which hydrophobic and charged units are uniformly distributed along the backbone, allowing direct comparison with composition-matched gradient or random analogues. Comparative experimental analysis reveals that sequence dictates interfacial behavior: the alternating architecture promotes more efficient engagement with lipopolysaccharide-rich membranes, leading to enhanced outer-membrane permeabilization, reduced hemolytic activity, and improved antibiotic potentiation. Molecular dynamics simulations provide a mechanistic basis for these observations by showing that alternating chains adsorb more favorably to the Escherichia coli outer membrane, adopt a curled conformation with extended cationic side chains more evenly exposed toward negatively charged LPS motifs, and maintain greater hydration during membrane insertion. Potential-of-mean-force and interaction energy analyses further indicate that the alternating sequence lowers the free-energy and dehydration penalties associated with productive membrane engagement relative to a gradient or random architecture. Together, the experimental and computational results support a model in which sequence-defined spatial organization controls chain conformation, hydration, interfacial energy landscapes, and membrane disruption thresholds. This work establishes alternating sequence as a programmable design parameter in amphiphilic polymers and expands sequence-controlled polymer chemistry to biologically relevant interfacial systems.