Synthesis,Polymerization Of The New Azide Monomers And Applications Of The Azide Polymers

Azide groups are high energy groups and reactive groups, which can be transformed into a variety of functional groups. So the chemistry of azides has attracted great attention of chemists, and organic azides have become very useful intermediates in synthetic chemistry. With the development of the polymer science, the synthesis and application of the azide polymers have also attracted much interest of polymer scientists, and synthesis methods were got rid of the stale and brought forth the fresh. Azide polymers are used widely as high energetic materials, cross-linking materials and the materials for surface modification. At the earlier development stage, azide polymers were commonly prepared by chemical modification of polymers or by cationic ring-opening polymerization of cyclic ether azides. However, these approaches have some disadvantages, azide content in the polymer produced by chemical modification couldn't be controlled very well, and ionic polymerization requires stringent reaction conditions such as high purity of monomers and high vacuum techniques. With the rapid development of the living radical polymerization especially RAFT polymerization and the further understanding of the azides, azide polymers with novel structure have been synthesized through the living radical polymerization. We have been trying to develop facile and effective strategies for the preparation of azide polymers, and living free radical polymerization has been first successfully used to prepare different azide polymers by y-ray initiation in our lab. In this thesis, we have designed and synthesized a series of new vinyl azide monomers based on the relationship between molecular structure and chemical property. We have explored the stability and polymerization character of the new vinyl azide monomers, and developed the new methods for the synthesis of the azide polymers. The application research of azide polymers have also been carried out as cross-linking materials and surface modification materials, and functional polymers. The main results obtained in this thesis are listed as follows: 1. Considering the relationship between molecular structure and chemical property, we have designed and synthesized different unsaturated azide monomers, including unsaturated ester azides, unsaturated acrylamide azides, styrene azides and allylazides. The stability of the new azide monomers has been explored. According to the structure of the azide monomers, we have investigated the cationic polymerization and living free radical polymerization of the monomers. From the results of the experiments, the structure influences in the stability and polymerization character of the azide monomers have been understood.2. A new vinyl aryl azide monomer,4-azidophenyl methacrylate (APM), has been synthesized. The thermal stability of APM has been investigated by temperature-dependent FT-IR spectroscopy and 1H NMR, and the monomer has been demonstrated to be quite stable at ambient temperature. Reversible addition-fragmentation chain transfer (RAFT) homopolymerization and copolymerizations of APM with methyl acrylate, methyl methacrylate, and styrene have been carried out at room temperature using a redox initiator, benzoyl peroxide (BPO)/N, N-dimethylaniline (DMA). The results show that the polymerizations bear all the characteristics of controlled/living free radical polymerizations. Moreover, the cycloaddition of azido group to carbon-carbon double bond can be avoided in the polymerization process at room temperature.3. A new vinyl azide monomer,2-chlorallyl azide(CAA), has been synthesized from commercially available reagent in one step. Owing to the allyl structure of CAA, the azide polymer could not be prepared via living free radical hompolymerization. However, the reversible addition fragmentation chain transfer (RAFT) copolymerization of CAA with methyl acrylate (MA) was carried out at room temperature using a redox initiator (BPO/DMA), in the presence of benzyl 1H-imidazole-1-carbodithioate (BICDT). The polymerization results showed that the process bears the characteristics of controlled/living radical polymerizations, such as the molecular weight increasing linearly with the monomer conversion, the molecular weight distribution being narrow, and a linear relationship existing between ln([M]o/[M]) and the polymerization time. Chain extension polymerization was performed successfully to prepare block copolymer. Furthermore, the azide copolymers were functionalized by Cu1-catalyzed "click" reaction with alkyne-containing poly(ethylene glycol) (PEG) to yield amphiphilic graft copolymers with hydrophilic PEG side chains. Surface modification of the glass sheet was successfully achieved via the crosslinking reaction of the azide copolymer under UV irradiation at ambient temperature.4. Homogeneous dispersion of pristine multi-walled carbon nanotubes (MWNTs) in various organic solvents was achieved using azide copolymer, poly(4-azidophenyl methacrylate-co-methyl acrylate)(P(APM-co-MA)), by a simple ultrasonic process. The copolymers were noncovalently attached to the surface of the MWNTs viaπ-πinteractions to form the MWNT-P(APM-co-MA) composites. The composites were characterized by transmission electron microscopy, thermogravimetric analysis, Raman spectra and UV-vis spectra. Then the dispersion solution of the MWNT-P(APM-co-MA) composites was used to fabricate superhydrophobic cotton fabric by a facile dip-coating approach. MWNTs were covalently attached on the surface of cotton fabric through the chemical reaction of the azide groups of P(APM-co-MA) with both MWNTs and cotton fibers based on nitrene chemistry under UV irradiation. Owing to introducing the nanoscale roughness of MWNTs, the surface of the cotton fabric was transformed from hydrophilicity to superhydrophobicity with an apparent water contact angle of 154°. Since MWNTs were covalently attached on the surface of the cotton fabric, the superhydrophobicity possessed high stability and chemical durability.5. Amphiphilic triblock azide copolymers containing poly(ethylene glycol) (PEG) and poly(2,2,3,4,4,4-hexafluorobutyl acrylate) blocks have been synthesized through room temperature RAFT polymerization using redox initiation and were successfully used to fabricate superhydrophobic cotton fabric by a facile approach. The copolymers were covalently attached to the surface of the cotton fabric by the reaction of azide groups with the cotton fibres based on nitrene chemistry via UV irradiation. Due to the amphiphilic character of the copolymer, hydrophilic PEG blocks tend to locate in the interface between the block copolymer coating and cotton fibres due to the H-bond interaction of PEG with the hydroxyl groups of the cotton fibres, and the fluorinated blocks aggregate in the outermost of the coating. And so the cotton fabric was transformed from hydrophilicity to superhydrophobicity with a water contact angle of 155°. Since the fluorinated polymer chains were covalently attached on the surface of the cotton fabric, the superhydrophobic cotton fabric possessed high stability and chemical durability.6. Amphiphilic triblock copolymers with the carbazole pendants have been synthesized by the combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and "click" chemistry. First, the triblock copolymers of 4-vinylbenzyl azide were prepared in the presence of the macromolecular chain transfer agent. Then, novel triblock copolymers were obtained via the click reaction between azide groups in the polymers and N-propargyl-carbazole. The copolymers were characterized by GPC,1H NMR spectra and FT-IR spectra, and the results indicated that the copolymers possessed well-defined structures. Due to the unique amphiphilic structure, the copolymers were self-assembled to form cup-shaped vesicles in a mixture solution of water and tetrahydrofuran. It is interesting to find that the copolymer vesicles show the phenomenon of aggregation-induced emission enhancement (AIEE), comparing with the fluorescence emission intensity in the solution of organic solvents.