| This dissertation focuses on the development of novel side-chain-type sulfonated polyimides (SPIs) with high performance suitable for polymer electrolyte fuel cell (PEFC) application.Rapid advances of fuel cell technologies for power generation and transportation have created an increasing demand for novel high-performance polymer electrolyte membranes (PEMs). Fuel cells of this type have been considered as a promising alternative energy source because of their high efficiency at low temperatures, ease of construction, and low environmental impact. The PEMs based on the perfluorosulfonic polymers such as Nafion, Flemion, etc, have been used for practical PEFC systems due to their high proton conductivity, superior chemical stability and good mechanical property. However, further progress in this area has been restricted by the insufficient performance of these membranes. In addition to the very high cost, these perfluorinated polymer electrolytes could not be used at temperatures higher than 100 C. Above this temperature, dehumidification of the hydrophobic perfluorinated matrix causes a dramatic decrease in the proton conductivity. Another important drawback is related to the inability of these membranes for the applicatioin in direct methanol fuel cell (DMFC), considered as an attractive option for the automotive industry, due to their high methanol crossover.These are the major reasons stimulating intensive research and development of novel polymer electrolytes with high proton conductivity, good membrane stability, low fuel/oxidant crossover and low cost. Many nonsulfonated PEMs by sulfonating hydrocarbon aromatic polymers such as polysulfones, polyether ether ketones, polybenzimidazoles and polyimides have been developed for fuel cell applications, among which sulfonated polyimides have been reported to be promising materials for PEFC applications. SPIs with sulfonic acid groups directly bonded to the polymer backbones (noted as main-chain-type) have been widely studied. Initially developed SPI from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and 2,2'-benzidinedisulfonic acid (BDSA, a commercially available sulfonated diamine) showed poor water stability. Consecutively, other main-chain-type SPIs with high proton conductivity and much better water stability were developed from NTDAand novel sulfonated diamines such as 4,4'-bis(4-aminophenoxy)biphenol-3,3'-disulfonic acid (BAPBDS).Nation membrane is known to have a microphase-separated structure and the ion-rich domains form channels being favorable for proton transport. In addition, the hydrophobic polymer backbone of Nafion imparts its good mechanical strength and excellent water stability. To mimic the structure of Nafion, the sulfonic acid should be attached to a side chain as a pendant group, and such a side-chain-type polymer might have different properties from those of main-chain-type ones. This thesis mainly focuses on the synthesis, proton conductivity, water stability and methanol permeation properties of a series of novel side-chain-type SPI membranes (with sulfonic acid groups in the side chains) in order to clarify "structure-property" relationship. Side-chain-type SPI membranes with high proton conductivity, good water stability as well as low methanol permeability were successfully developed.In chapter 2 and chapter 3, several novel sulfonated diamine monomers, 3-(2',4'-diaminophenoxy)propane sulfonic acid (DAPPS), 2,2'-bis(3-sulfopropoxy)benzidine (2,2'-BSPB) and 3,3'-bis(3-sulfopropoxy)benzidine (3,3'-BSPB), were successfully synthesized and the sulfonated polyimides were prepared from NTDA, DAPPS, BSPB and other nonsulfonated diamines. Transmission electron microscopy (TEM) proved that the BSPB-based homo-SPI had a microphase-separated structure composed of hydrophobic domains and hydrophilic ionic domains with an average size of 5nm. Thermogravimetry-Mass spectrometry analysis revealed that these side-chain-type SPI membranes were thermally stable up to 230-250 C. All the side-chain-type SPI membranes showed re...
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