Synthesis And Application Of Novel Cellulose Derivatives Via Thiol-ene Click Reactions

With an increasing depletion of the oil resources and pollution of the environment,problems caused by the oil-based polymers,which are not renewable or biodegradable,are increasingly severe.Nowadays,science and technology move to application of renewable biomass resources due to their environmental friendly and sustainable properties.As the most inexhaustible and common raw material on the earth,cellulose and its derivatives are indispensable parts of our life.However,the application of cellulose is limited because it is difficult to be processed in the melt state or in general solutions.Cellulose can be dissolved in alkali/urea aqueous solutions in a short period of time.This solvent has been proved to be an ideal environment for the etherification of cellulose.In this thesis,allyl cellulose(AC)was synthesized in alkali/urea solutions for the first time.Thiol-ene click reaction between AC and thiol compounds was drawn into the modification of cellulose.Novel cellulose derivatives with different structures and properties were successfully prepared,and their applications were investigated.The novel creations of this work are as follows.(1)AC was synthesized in alkali/urea aqueous solutions for the first time,and its thiol-ene click reaction with thiol compounds were investigated.(2)Cellulose-based micelles(MCs)were fabricated by the self-assembly of AC-Cys-NDM,which was synthesized from the thiol-ene click reaction of AC.MCs was used as the soft templates for the preparation of Ag@MC nanocomposite micelles with excellent catalytic activity.(3)Novel fluorescent cellulose derivatives(AC-AET-DMANM)were successfully synthesized from the thiol-ene click reaction,and which were applied in detections of aromatic compounds and Cu2+ in non-aqueous/aqueous media.(4)AC-AET-DMANM was mixed with the amino-modified cellulose nanocrystals(ACNC)to prepare the nanocomposite films,which showed both fluorescence and liquid-crystal behavior.The main content and conclusions in this thesis are divided into the following parts.Firstly,allyl celluloses(ACs)were synthesized by the reaction of cellulose with allyl chloride in NaOH/urea aqueous solutions.The reaction started homogeneously and ended heterogeneously,which provides the obtained AC with a high DS and facilitates its purification.The structure and properties of ACs were characterized with SEC-LLS,NMR and solubility testing.The total DS of the AC increased from 0.98 to 1.65 with increasing molar ratio of allyl chloride to AGU from 9:1 to 24:1.All the AC samples showed a high solubility in organic solvents such as DMSO,DMAc and DMF.A capability evaluation of the click reaction of AC was performed by selecting four thiol compounds:n-dodecyl mercaptan(NDM),2-aminoethanethiol hydrochloride(AET),cysteine(Cys),monothioglycerol(MG).AC-click products were characterized with FT-IR,NMR and elemental analysis,and the results indicated few impurities or substructures resulting from side reactions.The click reaction displayed a high conversion rate,and all the AC-click products demonstrated high solubility in certain solvents.A series of AC-Cys-NDMs were successfully synthesized from the thiol-ene click reaction.They were found to be micelles(MC)in water by self-assembly.The size of MC was controlled by the DS of the hydrophobic chain(NDM).Ag nanoparticle(AgNPs)/MC composite(Ag@MC)micelles were fabricated by using MC as the soft template and protective agent in photo-reduction.Contents of AgNPs were similar in all the composite micelles.The size of AgNPs increased from 3 nm to 15 nm with increasing size of the MC template.AgNPs were stabilized by MC through the interaction between Ag and S atoms.Ag@MC nanocomposite micelles exhibited excellent catalytic activity and recycle stability for the reduction of p-nitropheonl to p-aminophenol by NaBH4,and the reaction followed the first-order rate law.A series of novel fluorescent cellulose derivatives(AC-AET-DMANM)with different DS were successfully synthesized.Allyl cellulose(AC)was firstly prepared from cellulose in NaOH/urea aqueous solution,and then 2-aminoethanethiol(AET)was introduced onto the cellulose backbone via thiol-ene click reaction.Finally,the fluorescent groups were introduced by reaction of the amine modified AC with 4-dimethylamine-1,8-naphthalic anhydride(DMANA).AC-AET-DMANM with lower DS(<0.25)was soluble in DMSO,and a relevant product was modified by further thiol-ene click reaction to provide a water-soluble fluorescent cellulose derivative(AC-AET-DMANM-2W).The structure and fluorescent properties of these derivatives were characterized by elemental analysis,FT-IR,1H NMR,UV-vis and fluorescence spectroscopy.AC-AET-DMANM of DS<0.09 displayed stable fluorescence in DMSO solutions and even in the solid state.The emission of AC-AET-DMANM(DS=0.09)in DMSO quantitatively and sensitively responded to 2,4-dinitrophenylhydrazine and 2,4,6-trinitrophenol by fluorescence quenching,and the limit of detection was 9.9×10-8 and 1.38×10-7 mol/L,respectively.AC-AET-DMANM-2W presented a selective,fast and linear response to Cu2+ in aqueous solution with a detection limit of 8.2×10-8 nol/L.These observations illustrate a high applicability of the novel fluorescent cellulose derivatives to the detection of specific chemical entities in aqueous/non-aqueous media.Nanocomposite films were prepared from the mixtures of water-soluble fluorescent cellulose derivative AC-AET-DMANM-2W(coded as FC)and the amino-modified cellulose nanocrystals(ACNC).FC and ACNC in the composites showed excellent miscibility due to electrostatic interactions.All the composite films showed both fluorescence and liquid-crystal behavior.The fluorescence intensity linear correlated with the content of FC.With an increase of ACNC content,the crystallinity of the films enhanced and iridescence appeared.Compared with the pure ACNC film,phase transition temperature of FC/ACNC films significantly raised.Fluorescence,liquid-crystal behavior and crystallinity were mutual independence without influence from the other component.It is facile to fabricate the films with certain fluorescence,crystallinity and hydrophobicity properties by simply adjusting the content and ratio of FC and ACNC.The results mentioned above proved that alkali/urea aqueous solution was a suitable solvent and reaction medium for the synthesis of AC.A variety of novel cellulose derivatives could be easily obtained from the thiol-ene click reaction between AC and thiol compounds.It provided a new pathway for the synthesis of cellulose derivatives and fabrication of novel cellulose-based materials.Therefore,this work is proved to be innovative and practical.