Synthesis And Application Of Immobilizing Quaternary Ammonium N-halamine Precursors For PU Membrane Surface Modification

Pathogenic bacteria breeding added to threat caused by infectious diseases and water-related diseases. Moreover, microorganism contamination on fiber adds to risk of cross infection. It is especially important to conduct researches on developing antimicrobial agents and coating materials which aim to deal with bacteria-related problem as a result. As a kind of effective, rechargeable antimicrobial agent against a wide spectrum of microorganisms, N-halamines were used extensively in areas such as antimicrobial material preparing and water dealing. However, N-halamine cannot be used repeatedly and caused pollution to environment. On the other hand, low hydrophilicity of N-halamines especially when they are grafted onto material hampered bacterial killing process of N-halamine. Moreover, two approaches applied widely to immobilize N-halamines(precursors) are polymerization and chemical grafting via tethering group. There still lacked an easy method to realize directly covalent immobilization of N-halamines on materials especially inert materials. As a result, we synthesized immobilizing quaternary ammonium N-halamine precursors for polyurethane(PU) membrane surface modification, then photo-grafted them covalently onto PU membranes using perfluorophenyl azide(PFPA) group as bonding group. Antimicrobial activity of modified PU membranes was then confirmed. The mainly researches were as follows:(1) In this thesis, N-halamine precursors 1-3 containing QAS group with different alkyl chain lengths were synthesized by N-alkylation, quaternization, ion-exchange and azidation using DMH as starting material with a yield of 59.6%-66.5%. We also synthesized N-halamine precursor 4 without QAS as control in surface modification and antimicrobial test of membranes. Structures of all compounds and intermediates were then confirmed by 1H NMR, 13 C NMR and HRMS.(2) N-halamine precursors 1-4 were photo-grafted onto PU membranes at UV irradiation(254 nm, 1.01 J/cm2, distance 5 cm), realizing immobilization of N-halamine precursors on PU membranes. Modified PU membranes were charactered by X-ray photoelectron spectroscopy(XPS) to confirm successful immobilization of N-halamine precursors on PU. F atomic contents on modified PU membranes revealed that shorter alkyl chains can promote photo-grafting of N-halamine precursors on PU. Contact angles of PU membranes showed that PU membranes containing QAS group presented better hydrophilicity than those without QAS group. Modified PU membranes were then chloridized by diluted bleach solution to convert N-H on membrane surface to N-Cl.(3) Antimicrobial activities of membranes treated with N-halamine precursors were performed by “Sandwich Test” method using E. coli(ATCC 25922) and S. aureus(ATCC 25923) as challenging strains. Antimicrobial tests showed that introduction of QASs increased antimicrobial activity of PU membrane. This was might because QAS moiety can enhance hydrophilicity of PU membrane while electrostatic attraction between QAS and bacteria enhance bacteria killing of N-halamines on membranes. PU containing longer alkyl chains(nine-(CH2)-) showed the highest antimicrobial activity, which was might because higher hydrophilicity and higher roughness can promote better adhesion of bacteria on membrane. As a result, modified membrane showed higher antimicrobial activity.