Quaternized Nylon-6 Polymers via Ring-Opening Polymerization of Cyclic Lysine Derivatives: A Versatile Antibacterial Platform

Nylon-6, while commercially essential, has proven challenging to endow with persistent antibacterial properties due to the lack of efficient and facile synthetic approaches. Poly(ε-lysine) derivatives have attracted considerable research attention due to their structural backbone similarity to that of nylon-6. Capitalizing on this structural similarity, herein, we achieved hydrophobicity-tunable quaternized nylon-6 polymers through rational design of side-chain structures in lysine-derived cyclic monomers and controlled quaternization reactions. By precisely controlling the quaternization process, amphiphilic quaternized nylon-6 polymers with adjustable hydrophobicity and cationic charge density were successfully prepared, enabling systematic evaluation of their broad-spectrum antimicrobial properties. Notably, enhanced hydrophobicity was found to significantly improve antibacterial efficacy against both <i>Escherichia coli</i> and its biofilms, with the amphiphilic polymers demonstrating superior antimicrobial performance. Furthermore, these amphiphilic quaternized nylon-6 polymers exhibited a thermoresponsive behavior. This work proposes a new design strategy for antimicrobial nylon-6 polymers, enabling the simultaneous enhancement of antibacterial functionality and the incorporation of temperature-responsive properties.