Design of intrinsically antibacterial PA6 through pyridine functionalization and surface quaternization

A salt-based strategy enables PA6 copolymers with pyridine units in the backbone. • The incorporated pyridine groups provide intrinsic reactivity for surface quaternization. • Surface quaternization is achieved without polymer dissolution or harsh conditions. • Quaternized PA6/6P shows strong antibacterial activity with minimal loss of mechanics. Polyamide 6 (PA6) is widely used in textiles, automotive components, and consumer products due to its adequate mechanical strength, chemical resistance, and processability. However, conventional PA6 is prone to microbial colonization, leading to odor, material degradation, and potential health risks, which limits its application in hygiene-sensitive areas. Herein, we report a strategy to construct interface-activated antibacterial PA6 by integrating main-chain pyridine units with surface quaternization. A semi-aromatic pyridine-3,5-dicarboxylic acid/hexamethylenediamine salt was first synthesized in water with high yield and subsequently copolymerized with ε-caprolactam via hydrolytic ring-opening polymerization, affording PA6/6P copolymers with controlled molecular weight (relative viscosity 2.30–2.40) and good processability. Incorporation of rigid pyridine units enhanced chain rigidity and thermal stability (Td >390 °C) while maintaining favorable melt rheology and improved mechanical strength (tensile strength up to 78.6 MPa). Importantly, the embedded pyridine moieties served as intrinsic reactive sites for post-polymerization surface quaternization through a simple immersion in 1-bromooctane and ethanol, yielding quaternized q-PA6/6P materials. Surface analysis confirmed successful formation of immobilized pyridinium groups at the polymer interface. The resulting q-PA6/6P exhibited good contact-active antibacterial performance, with the 48 h quaternized sample almost completely inhibiting the growth of Staphylococcus aureus and Escherichia coli . Download: Download high-res image (135KB) Download: Download full-size image