Antibacterial activity of polymeric quaternary ammonium compounds tuned by incorporating hydrophilic co-monomer

Abstract

Copolymers of quaternary ammonium monomer(QAM) and hydrophilic co-monomer were successfully synthesized by free radical polymerization. It was discovered that the hydrophilic co-monomers with poor antibacterial activity significantly enhanced the activity of QAM substituted with a long alkyl chain[i.e., N,N-dimethyl-N-dodecyl methacrylate ammonium bromide(DMAEMA-DB)]. When a suitable molar ratio of DMAEMA-DB to co-monomer was selected, the activity of the copolymers was up to 123 times that of the homopolymer of DMAEMA-DB against S. aureus, and 282 times that of it against E. coli. But unlike DMAEMA-DB, the co-monomers might weaken the activity of QAM substituted with a short alkyl chain[i.e., N,N-dimethyl-N-butyl methacrylate ammonium bromide(DMAEMA-BB)]. Moreover, it was found that copolymers of DMAEMA-DB were much more biocidal than those of DMAEMA-BB. Therefore, it could be speculated that the long alkyl chain plays an important role in the antibacterial activity, and that the hydrophilic co-monomers are beneficial to polymeric guaternary ammonium compounds(PQACs) to exert the positive effect of the long alkyl chain to the greatest degree.