Homogeneous Synthesis, Properties And Applications Of Novel Cellulose-Based Polyelectrolyte Ethers

Recently, with the depletion of oil resources and increasing environmental pollution and the urgent need for sustainable development, cellulose, as an environmentally friendly renewable resource, has received more and more attention and been investigated extensively by both academic and industrial researchers. However, cellulose has not reached its potential applications because it cannot be melted to fabricate into a desired form or to be dissolved in a common solvent, attributing to its inter-and intramolecular hydrogen bonding. Based on the unique structure and reactivity of cellulose, chemical modifications play dominant roles in improving the overall utilization of this bioresource. The purpose of etherification of cellulose is to improve its hydrophilicity and solubility in aqueous media, through the introduction of substituents to the cellulose backbone to destroy its strong hydrogen bonds. Nowadays, all commercial cellulose ethers have been prepared with heterogeneous procedures with the cellulose slurry in industry, which prohibits effective synthesis of cellulose products with desired degrees of reaction, reproducible substitution patterns, and targeted properties at both the laboratory and industrial level. Therefore, homogeneous modification of cellulose has been one focus of cellulose research for a long time. In the present work, two kinds of novel cellulose-based polyelectrolyte ethers were homogeneously synthesized in NaOH/urea aqueous solutions for the first time, by using 3-chloro-2-hydroxy-propyltrimethylammonium chloride (CHPTAC) and acrylamide as etherification reagents. The structure, properties and applications of the obtained novel polyelectrolytes were well investigated and the results are presented in this thesis.The novel features of this work are as follows. (1) Quaternized cationic cellulose (QC) was homogeneously synthesized in NaOH/urea aqueous solutions for the first time. The structure, solution properties, flocculation properties and antimicrobial activities of the QC samples were investigated. (2) QC samples were studied as gene carriers for the first time, the effect of molecular weight (Mw) and degree of substitution (DS) of QC on the efficiency of gene transfection were investigated in detail. (3) QC nanoparticles were prepared by ionic crosslinked with sodium tripolyphosphate (TPP) in water and investigated as protein drug carriers. (4) Self-assembled micelles of hydrophobically modified QC were used as a delivery carrier for hydrophobic drugs. (5) Anionic cellulose polyelectrolytes (AMC) containing acylamino and carboxyl groups were homogeneously synthesized in NaOH/urea aqueous solutions. The structure and solution properties of AMC were well characterized. The main content and conclusions in this thesis are divided into the following parts. Quaternized cationic cellulose (QC) was homogeneously synthesized by reacting cellulose with CHPTAC in NaOH/urea aqueous solutions for the first time. The structure and solution properties of the QCs were characterized by using elemental analysis, FT-IR, 13C NMR, SEC-LLS, viscometer andζ-potential measurements. The results revealed that water-soluble QCs with DS value of 0.20-0.63 could be obtained by adjusting the molar ratio of CHPTAC to anhydroglucose unit (AGU) of cellulose and the reaction time. The QC solutions in water displayed a typical polyelectrolyte behavior, and theζ-potential values in pure water are in the range of 26-45 mV. The results of agarose gel electrophoresis assay suggested that QCs could condense DNA efficiently. QCs displayed relatively lower cytotoxicity as compared with PEI, and QC/DNA complexes exhibited effective transfection compared to the naked DNA in 293T cells.QCs with different Mw and DS were homogeneously synthesized in NaOH/urea aqueous solutions. The factors affecting the transfection efficiency e.g. Mw, DS, and N/P ratios have been evaluated by size andζ-potential measurements, agarose gel electrophoresis, TEM and in vitro transfection assay. The cytotoxicity of QCs and QC/DNA complexes were evaluated in 293 T cells and were found to be relatively low compared with 25 kDa PEI and PEI/DNA complex, and increased slightly with increasing of Mw and DS. The results revealed that the level of transfection efficiency was significantly influenced by Mw and DS of QC as well as N/P ratios. QC with Mw of about 8×104 g/mol and DS of about 0.6 displayed relatively higher transfection efficiency attributing to the intermediate stability. QC had a distinct advantage and maintained similar level of DNA tansfection efficiency regardless of the serum present in media. This work provided important information of scientific value for further development of QC for usage as safe and efficient nonviral vectors.QC nanoparticles were prepared in distilled water by ionic crosslinking of QC with sodium tripolyphosphate (TPP) for the first time. BSA as a model protein drug was used to investigate the loading and release features of the nanoparticles. The results indicated that QC nanoparticles had high loading efficiency and capacity for BSA. The particle size, BSA loading efficiency and capacity obviously increased with an increase of the initial BSA concentration. The release profile of QC nanoparticles showed a burst release at the first 2 h and then followed by a slowly sustained release. Increasing TPP concentration promoted BSA loading efficiency, reduced the burst release and delayed release. Increasing the DS of QC could reduce the particle size, enhance the zeta potential, promote BSA loading and slow the drug-release rate. All these investigations reveal that QC nanoparticles are potential vehicle for the protein drugs.The flocculation characteristics of QCs were evaluated in montmorillonite (MMT) suspensions and simulated dye (Reactive Red) aqueous solutions by spectrophotometry. The results showed that QCs were effective flocculating agents for MMT and Reactive Red dye over a wide range of pH values. The flocculation efficiency of MMT was up to nearly 100%, and decolorization efficiency of Reactive Red dye reached 93% under optimum conditions. The flocculation and decolorization efficiency of QCs increased with increasing DS, i.e. the higher DS, the lower the optimal dosage of QC. Moreover, QC could strongly inhibit the growth of Gram-positive bacteria (S. aureus) and Gram-negative bacteria (E. coli). Therefore, QC is applicable as a novel wastewater treatment agent with high flocculation efficiency as well as effective antimicrobial activity.Novel amphiphilic cationic cellulose derivatives (HMQC) carrying long chain alkyl groups as hydrophobic moieties and quaternary ammonium groups as hydrophilic moieties were synthesized. The structure and properties of HMQC were characterized by elemental analysis, FT-IR,1H NMR and TEM. The critical micelle concentration values (CMC) of HMQC in aqueous solution were determined by fluorescence spectroscopy. It showed that HMQC can self-assemble into polymeric micelles in water with an average particle diameter of about 50 nm. The cytotoxicity study showed that the HMQC exhibited low cytotoxicity. Prednisone acetate, a water insoluble anti-inflammation drug, was chosen as a model drug to investigate the utilization of self-assembled HMQC micelles as a delivery carrier for poor water-soluble drugs. The results showed that the prednisone acetate could be incorporated effectively in the self-assembled HMQC micelles and be control-released from the micelles gradually for 120 h. The novel HMQC micelles could be considered as promising drug carriers.Based on the Michael addition and the saponification of acylamino groups to a carboxyl groups in alkaline media, cellulose polyelectrolytes (AMC), containing acylamino and carboxyl groups, were homogeneously synthesized from cellulose with acrylamide in NaOH/urea aqueous solutions. The structure and properties of AMC were characterized with elemental analysis, FT-IR, NMR,ζ-potential measurement. The total DS and the DS of acylamino groups for the derivatives increased with an increase of the molar ratio of acrylamide to AGU and the cellulose concentration, while the DS of carboxyl groups hardly changed because of the similar hydrolysis conditions. The total DS values of the water-soluble derivatives are in the range of 0.36 to 0.84. The ζ-potential values of derivatives are in the range of-15 to-25 mV. The [η]values of the polyelectrolytes in NaCl aqueous solutions increased apparently with an increase of the pH value in the lower pH region and reached a relatively stable value at the pH range from 7 to 12.Solution properties of AMC were investigated by SEC-LLS, viscometer and rheometer. The results indicated that AMC could form large aggregates spontaneously in water with or without the addition of salts by the strong hydrogen bonds and electrostatic interactions between acylamino and carboxyl groups. Steady-shear flow study showed a Newtonian behavior of the solutions in the dilute regime while a shear-thinning behavior as the concentration increases. The critical concentration for transition from dilute to concentrated solution was determined to be 0.7 wt%. AMC solutions displayed good thermo-stability and reversible liquid-like behavior, and the influences of salt adding on the rheological behavior were negligible owing to the stiffness of the polymer chain. The derivation from Cox-Merz rule at relatively low concentration was related to the co-existence of single chain and large aggregates of AMC in dilute regime. As the polymer concentration increased, the AMC system was transformed into a homogeneous entanglement structure, resulting in the disappearance of deviations from the Cox-Merz rule.The basic research results mentioned above proved that NaOH/urea aqueous solution was a suitable solvent and reaction medium for the homogeneous synthesis of novel cellulose-based polyelectrolytes, which provided a new pathway for the preparation of cellulose derivatives. Meanwhile, this work clarified the relationships among the structures, properties and applications of the novel cellulose-based polyelectrolytes. This thesis provides important information and scientific evidence for the comprehensive utilization of cellulose and other renewable resources, as well as for the preparation of advanced functional materials through green methods. Therefore, it accords well with the target of the strategy of sustainable development, and possesses great scientific significance and prospects of applications.