| There is a growing demand on exploring clean, high efficiency and alternative energies, duo to the fast economic development and limited availability of fossil fuels. Fuel cells, as a promising solution, have received more and more attention, and this technology can convert chemical energy to electrical energy, directly and safely. As a key component in fuel cells, conductive ionomer plays a significant role in the performance of fuel cells. Anion exchange membrane has received much attention because it has many advantages over proton exchange membrane with respect of the crossover of menthol and the use of noble electrocatalysts. But there are still some problems for the application of anion exchange membrane, such as low ionic conductivity and low chemical stability in strong basic medium. In order to solve these problems, it is necessary to pay attention to the design and preparation of new membrane materials. It is well known that, Nafion exhibits outstanding properties as proton exchange membrane because of the backbone of perfluoropolymer, which leads to high stability of the membrane, and excellent electrochemical properties. Guanidine is a strong organic base, which shows high stability and ionic conductivity. In order to obtain a new kind of high-performance anion exchange membrane, we attempt to design and prepare the fluorinated polymers with functional groups of guanidinium based on the combination of their advantages of fluoropolymers and guanidinium. Although perfluoropolyme with guanidinium can be prepared, the structure of polymer can not be controlled. Living/controlled free radical polymerization has provided a powerful tool to synthesize well-defined fluoropolymers with predictable molecular weights, various architectures and narrow molecular weight distributions. However, there are few reports about living/controlled free radical polymerization of fluoroolefins. Therefore in this thesis, we investigate the synthetic methodology of well-defined fluoropolymer and polymer containing guanidium group. In order to achieve living/controlled free radical polymerization of fluoroolefins, we designed and synthesized several kinds of chain transfer agents and, investigated radical copolymerizations of fluoroolefins and nonfluoroolefins. Unfortunately, we found that fluorinated copolymer could not form a good film due to low molecular weight and the unique structures. Then we developed a new approach for preparation of pentasubstituted guanidine and utilized it to prepare anion exchange membrane containing quaternary guanidinium groups by the reaction between brominated poly(2,6-dimethyl-1,4-phenylene oxide)(BPPO) and pentasubstituted guanidine. Moreover, we also synthesized new monomers of guandine and guandinium and their polymers, and demonstrated that both of the guandinium monomer and its polymer have antimicrobial activity. The main results obtained in this thesis are listed as follows:1. The conventional radical copolymerization of chlorotrifluoroethene (CTFE) and vinyl ethers (phenyl vinyl ether and butyl vinyl ether) have been investigated. The experimental results show that, phenyl vinyl ether can not copolymerize with CTFE neither initiated by free radical nor under y-ray irradiation. However, the copolymerization of butyl vinyl ether and CTFE can proceed under free radical initiation. Meanwhile, we designed and synthesized S-benzyl O-ethyl dithiocarbonate (BEDTC), and performed copolymerization of CTFE and butyl vinyl ether in the presence of BEDTC at room temperature under60Co y-ray irradiation. The experimental results indicate that, the molecular weight of poly(CTFE-alt-BVE) increases linearly with the monomer conversion, molecular weight distribution remains narrow during the polymerization, and the polymerization is a first-order reaction with respect to the monomer concentration. By the chain extension polymerization, block copolymer with controlled molecular weight has been synthesized. All results indicate that the process possesses the natures of living/controlled free radical polymerization. The alternating structure of copolymers was confirmed by1H NMR,19F NMR and13C NMR. The thermal properties of the copolymer were also studied through TGA and DSC. This work open a new way for living/controlled free radical polymerization of fluoroolefins, which can be used for preparation of anion exchange membrane.2. P-chloromethyl styrene (CMS) is a common functional monomer, which can be used for synthesis of many kinds of functional polymers. Herein, we investigated the conventional radical copolymerization and RAFT copolymerization of CTFE and CMS. The conventional radical copolymerization of CTFE and CMS was initiated by BPO, and composition and structure of the copolymer were characterized by’H NMR and19F NMR. The results show that the copolymer possesses an alternating structure. Xanthate can be used as a chain transfer agent (CTA) for the living/controlled free radical copolymerization of fluoroolefins and non-conjugated monomers, such as vinyl acetate and N-vinyl pyrrolidone, but not effective for the other vinyl monomers. Here, We first used a trithiocarbonate, S-l-dodecyl-S’-(a,a’-dimethyl-a"-acetic acid)trithiocarbonate (DDMAT), as a RAFT agent for the RAFT polymerization of CTFE and CMS. The experimental results show that the polymerization possesses living/controlled natures of free radical polymerization. The molecular weight of poly(CTFE-alt-CMS) increases linearly with the monomer conversion. Molecular weight distribution remains narrow during the polymerization, and the polymerization is a first-order reaction with respect to the monomer. After the quaternization of poly(CTFE-alt-CMS), we found that quaterized polymer was hard to form the film. In order to improve the film-forming property, block copolymers of poly(CTFE-co-CMS)-b-poly(BA) were successfully synthesized using poly poly(CTFE-co-CMS)as macro-CTA. We hope the block copolymers can be suitable candidates for the study of anion exchange membrane. But since the time limited, the further work will be done in the future.3. In order to obtain guandinium polymers, we developed a new method for preparation of pentasubstituted guanidine,1,1,3,3-tetramethyl-2-benzyl guanidine. The reaction was carried out at room temperature by reaction of1,1,3,3-tetramethylguanidine (TMG) and benzyl chloride. Comparing with the traditional method, this new method has many advantages, such as simple purification prossesses, avoiding the use of oxalyl chloride or phosphorus oxychloride. Then the pentasubstituted guanidine was used to prepare anion exchange membrane by the reaction between brominated poly(2,6-dimethyl-1,4-phenylene oxide)(BPPO) and1,1,3,3-tetramethyl-2-(4-vinylbenzyl) guanidine. It was donstrated that the guandinium polymer from BPPO with52%bromination show excellent film-forming property. Therefore, the structure and properties of anion exchange membrane, including ion exchange capacity, water uptakes, swelling ratios, were investigated. Ionic conductivities of anion exchange membrane were assessed at different temperatures, and activation energy of ion transfer was also calculated. In addition, Thermal stability of anion exchange membrane is measured by TGA, and the chemical stability was estimated by the difference of ionic conductivity before and after immersing the membrane in1M NaOH solution at60℃for48h. All results show that the properties of anion exchange membrane can meet the requirement of fuel cells.4. A polymerizable guanidine,1,1,3,3-tetramethyl-2-(4-vinylbenzyl) guanidine (TMVBG), was synthesized by the nucleophilic reaction of1,1,3,3-tetramethylguanidine (TMG) and4-chloromethylstyrene (CMS). Then the kinetics of radical copolymerization of1,1,3,3-tetramethyl-2-(4-vinylbenzyl) guanidine and styrene is investigated. In order to understand polymerization behavior of the guanidine monomer, the reactivity ratios between styrene and TMVBG were accessed based on the methods of Fineman-Ross, Kelen-Tiidos and extended Kelen-Tiidos law. Moreover, by methylation reaction with CH3I, a styrene guanidinium,1,1,2,3,3-pentamethyl-2-(4-vinylbenzyl) guanidinium (PMVBG) was obtained. The homopolymer of PMVBG was prepared using AIBN as initiator. By the antibacterial activity test, it was demonstrated that TMVBG and its homopolymer show antibacterial activity against Staphylococcus aureus and Escherichia coli. As a result, the guandinium polymers can not only be used as candidate of anion exchange materials, but also novel antimicrobial materials. |
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