Controllable synthesis and antimicrobial activities of acrylate polymers containing quaternary ammonium salts

A series of acrylate polymers containing quaternary ammonium salts (PDMAEMA-BC) having tunable molecular weights were synthesized via atom transfer radical polymerization (ATRP), and the effect of the degree of polymerization (DP) on the antimicrobial activity against bacteria (Escherichia coli, Staphylococcus albus), pathogenic fungi (Candida albicans) and phytopathogenic fungi (Rhizoctonia solani and Fusarium oxysporum f. sp. cubense race 4) was systematically assessed. The antimicrobial properties against E. coli, S. albus and C. albicans were characterized using the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) or minimum bactericidal concentration (MBC) values, whereas the antimicrobial activities against R. solani and Foc4 were evaluated using the effective concentration (EC50 and EC90), MIC and MFC values. The results indicated that the PDMAEMA-BC homopolymers showed better antimicrobial activities than the corresponding monomer, i.e., the acrylate quaternary ammonium salt monomer (DMAEMA-BC), and the optimal antimicrobial activities were obtained for moderate PDMAEMA-BC chain lengths. These results help to understand the antimicrobial mechanism of polymeric quaternary ammonium salts and highlight their potential application as fungicidal agents for controlling both human and plant diseases.