Preparation Of Cationic Polyurethane With Antibacterial And Fluorescent Properties

With the development of the society,environmental protection is becoming a great issue.Bacterial and antibacterial materials haves been gaining more and more attention.Traditional antibacterial materials such as chitosan,metal oxide,quaternary ammonium salt and quaternary phosphonium salt have many disadvantages,such as for examples,poor heat resistance,poor durability,easy loss during use,and certain level of toxicity.Therefore,use of polymers with quaternary ammonium salt as antibacterial agents appears as an effective alternative.Polyurethane is one of the most common and widely used biomedical polymers.On one hand,the coordination of quaternary ammonium group with polyurethane can achieve repeated use,and on the other hand,it makes the antibacterial group easierto concentrate on the surface of the carrier.Therefore,the product is efficient in sterilization,becoming the focus of current research and development.Nowadays,new efficient luminescent materials have become a research focus.Compared with luminescent materials of small molecule compounds,luminescent polymers have high luminescence efficiency,excellent processing and film forming performance,and strong structural stability.Because of the aggregation caused quenching（ACQ）effect,the fluorescence emission is greatly reduced or even vanished at high concentration for most of the classical compounds of small molecules with typical chromophores,and low concentration is compulsory for their emission,limiting therefore their applications.On the contrary,molecules and polymers by aggregation-induced emission（AIE）need to have a high concentration to be emissive,and even in solid state.Luminescent polymers with both properties are rarely reported.Based on the above analysis,a cationic polyurethane PUn was synthesized with both excellent antibacterial and luminescent properties.First,using N-methyl diethanolamine（MDEA）and a series of alkylation reagents alkyl iodides,from methyl,ethyl and up to octadecane,i.e.n=1,4,8,12,16,18 for C_nH_2n+1I,quaternary ammonium salts of different alkyls,i.e.MDEAn with n=1,4,8,12,16 and18,were prepared.By precipitation polymerization of TDI and MDEAn,between NCO groups of TDI and the hydroxyl groups of MDEA,a set of cationic polyurethanes,PUn with n n=1,4,8,12,16,18,were prepared,with TEA as the catalyst in acetone as the solvent.The structures of MDEAn and PUn were characterized by Fourier transform infrared spectroscopy（FTIR）and nuclear magnetic resonance（¹H-NMR）.The antibacterial properties of PUn were studied.The results,judged by the minimal inhibitory concentration（MIC）,showed that PUn samples could inhibit the growth and reproduction of Escherichia coli,and the inhibitory effect could enhance with the increased concentration of PUn.In addition,among all the prepared PUn,PU12 showed the best antibacterial activity against Escherichia coli.The antimicrobial mode of PU12 was contact sterilization.The fluorescence emission of PUn was characterized,and the emission mechanism was discussed.It was found that the emission behavior of PUn was not subjected to concentration,and the emission was effectively observed from low to high concentration,and even in solid state.When the excitation wavelength was placed at 290 nm,PUn solutions emitted at around 350 nm with a slight fluctuation for the maximal emission position depending on the length of the side alkyl group,and the emission intensity increased first,reached a maximum at concentration of 0.1mg/mL and then decreased with further increase in PUn concentration.When the excitation wavelength was increased to 320 nm,PUn solutions emitted at around 358nm,and the emission intensity increased first,reached a maximum at concentration of1 mg/mL,and then decreased with further increase in PUn concentration.With PUn concentration at 10 mg/mL or higher,the solution showed almost no fluorescence.However,when the excitation wavelength increased to 350 nm,new fluorescence emission appeared at 450 nm in the visible region,and the fluorescence intensity increased with the increase of concentration.The fluorescence in the ultraviolet region comes from the interaction between benzene ring and carbamate group in the molecular chain,and the fluorescence in the visible region comes from the aggregation of molecular chain.The appearance of aggregates was verified by UV spectra and DLS results of PUn solution,and the size of aggregates increased with the increase of solution concentration.The movement ability of PUn was affected by changing the solution temperature and adding bad solvent.The results showed that any restriction of molecular movement would enhance its fluorescence emission.The whole antibacterial process was characterized by the change of PU12EL fluorescence intensity by fluorescence method.Considering the other components in the mixed system might affect the change of fluorescence intensity,LB liquid medium,PU12HL and EL were tested respectively with excitation wavelengths of 300 nm.It was proved that the fluorescence intensity of LB liquid medium and PU12 did not change with the increase of culture time.For the mixed system of Escherichia coli and LB liquid medium,due to the absence of antibacterial agents and sufficient nutrition,escherichia coli reproduction led to turbidity of the system,affecting the light transmittance of the system,so the fluorescence intensity of the system decreased.For PU12EL,the fluorescence intensity of PU12EL decreased gradually within 0-24 h,indicating that e.coli was killed or inhibited by PU12 fungicide during this process.When the culture time exceeded 24 h,the fluorescence intensity of PU12EL was basically unchanged,indicating that the sterilization process had basically ended.The reasons for the decrease of PU12EL fluorescence intensity can be explained as follows:When the excitation wavelength was 300 nm,the fluorescence emission peak of PU12EL at 355 nm was generated by the superposition of PU12,LB liquid medium and E.coli.PU12EL was adsorbed on the surface of negatively charged bacteria and contacted with positively charged antibacterial agents,then penetrated the cell wall and combined with the lipid layer and protein layer of the cell membrane,destroying the amino acids in the protein.However,amino acids were the main luminescent components in E.coli,so the fluorescence intensity of PU12EL decreased at 0-24 h.