Preparation Of Alkyl-substituted Imidazolium-based Poly(Ionic Liquid) Brushes And Their Antibacterial Properties

The discovery of antibiotics has made the diseases caused by bacterial infections such as pneumonia and influenza no longer the primary cause of human death.However,the abuse of antibiotics makes drug-resistant bacteria one of the major threats to human health.Therefore,the development of safe and effective antibacterial materials is of great importance to reduce bacterial infection and to broaden the application of antibacterial materials.In a wide range of antibacterial materials,poly?ionic liquid?s?PILs?have cationic groups and alkyl substituents in each repeating unit,which endows them an desirable antibacterial activity.The cation of PILs can generate strong electrostatic interaction with the anion on the surface of bacterial cell membranes,and disturb the structure of bacterial cell membrane.The hydrophobic alkyl side chains of PILs can penetrate into the lipid bilayer to promote the rupture of bacterial cell,and accordingly kill bacteria including drug-resistant bacteria,reducing the possibility of emergence of drug-resistant bacteria.The PIL brushes formed on material surface through covalent bonds provide an excellent antibacterial performance to the substrate,keeping high antibacterial efficiency in a long period.Therefore,it would be an effective method to preparing an antibacterial material.However,few reports on PIL antibacterial brushes are available so far.Furthermore,there is still not systematic research on the relationship between the structural characteristics of PIL brushes and their antibacterial properties.So,this thesis focuses on the control of PIL brushes'grafting density and thickness,the antibacterial performance and cytotoxicity of PIL brushes.Imidazolium-based ionic liquid monomers[VBMI⁺][BF₄^-]?[VBEI⁺][BF₄^-]and[VBBI⁺][BF₄^-]were first synthesized,and then the corresponding imidazolium-based PIL brushes were prepared by surface-initiated ATRP reaction.A"degrafting initiator"method was used to adjust the relative grafting density of the PIL brushes.The relative molecular weight and thickness of the PIL brushes were controlled by the ATRP reaction time.The structure of the PIL brushes was characterized by XPS,spectroscopic ellipsometry,and other characterization methods.The results show that the relative grafting density of PIL brushes increases linearly with the increase of surface initiator density,and the thickness of PIL brushes increases linearly with the increase of ATRP reaction time.These results mean that the controllability of PIL brushes can be easily achieved.The effects of relative grafting density,relative molecular weight,alkyl substituent,and surface Zeta potential on antibacterial performance of imidazolium-based PIL brushes were systematically studied.It was found that the charge effect is the key to the antibacterial performance of imidazolium-based PIL brushes.As the relative grafting density of PIL brushes increased from 0.50 to 1.31,the surface Zeta potential increased from 26 mV to 68 mV,and the antibacterial rate of S.aureus increased from 75%to 90%within 1 h.Similarly,as the relative molecular weight of PIL brushes increased from 12.5 kDa to 33.4 kDa,the surface Zeta potential increased from 35 mV to 70 mV.The antibacterial rate of S.aureus increased from 64%to 86%within 1 h.At the same time,the antibacterial activity of the PIL brushes is also related to the type of bacteria.The antibacterial effect of PIL brushes against Gram-negative bacteria is more profound than that against Gram-positive bacteria due to the higher electronegativity and hydrophilicity of the Gram-negative bacteria.It should be pointed out that the antibacterial rate could still maintain about 95%within 5 hours after the PIL brushes were recycled for 5 times.The cytotoxicity test indicates that PIL brushes have almost no significant cytotoxicity to cell L929 and 3T3.The PIL brushes with high antibacterial performance and high stability are expected to be a promising application in food processing,medical materials and other fields.