N-(2-hydroxypropyl)-3-trimethylammonium chitosan-poly(ɛ-caprolactone) copolymers and their antibacterial activity

Chitosan-poly(ɛ-caprolactone) (CPC) copolymers were synthesized via an amino-group-protection method. Selected CPCs with poly(ɛ-caprolactone) content less than 50 wt.% were further modified by introducing quaternary ammonium groups. It was found that the maximum degree of quaternization for some quaternized CPCs (q-CPCs) could reach around 38% under present synthesis conditions. The optimized q-CPCs showed various antibacterial activities in vitro, and they were able to completely prevent growth of Staphylococcus aureus and Escherichia coli at different concentrations of about 0.2% and 0.25%, respectively. At lower concentrations, these optimal q-CPCs had higher antibacterial activities against both bacteria as compared to chitosan. The optimized q-CPCs were also processed into membranes for tensile mechanical investigations, and the resulting membranes exhibited notably higher strength and modulus in wet state but much lower strength and modulus in dry state when they were compared with chitosan membranes. Results suggested that the optimal q-CPCs with proper compositional proportions could have the potential for certain kinds of antibacterial applications where desirable tensile strength in wet state is required.