| Polymer exchange membrane fuel cells (PEMFCs) are the rapidly developing fifth-generation fuel cell. With the lowest working temperaturethe highest specific energy, the fastest startup, the longest service life, and the widest applications, PEMFCs have received widely investigated as a promising new power sources for vehicles and portable devices. Proton exchange membrane is a key component of the PEMFC for transferring protons from the anode to cathode as well as providing a barrier to the fuel gas cross-leaks between the electrodes. The membranes traditionally used in PEMFC are perfluorosulfonic polymers such as Dupont Nafion?. Although they show superior performance in fuel cells operating at moderate temperatures (<90oC) and high relative humidity with pure hydrogen as fuel, the high cost, low conductivity at low humidity or high temperature and high methanol permeability of Nafion? have limited their usages. Hence alternative proton exchange membrane materials are being sought. For instance, recently our groups have explored several sulfonated poly(aryl ether)s (SPAEs) for proton exchange membranes usages. Although they show very good potential usages in PEM, there still have several drawbacks to solve. (1) SPAEs with low IEC exhibited good mechanical strength and methanol resistance. However, their low proton conductivity restricts the performance in fuel cell. (2) SPAEs with high IEC exhibited superior proton conductivity. However, the brittleness of the membranes at evaluated temperatures, excessively swelling properties and the relatively high methanol crossover in membranes has limited their usages.In order to solve these problems and improve selected PEM properties, two methods were proposed in this dissertation: (1) block copolymers; (2) acid-base blend membranes.In chapter 2, block SPAEK copolymer ionomers were successfully synthesized by a two-stage process. First, the hydrophobic block with controlled length on average was prepared. And then, the monomers with desired stoichiometry were added in order to prepare and control the length of the hydrophilic block. Each block copolymer was then composed of an alternating sequence of several hydrophilic and hydrophobic blocks. Further we have characterized the structures in detail.In chapter 3, the morphology of block SPAEK membranes was detailed investigated by various measurements, including small angle X-ray scattering (SAXS) and transmission electron microscope (TEM). As observed by TEM, spherical ionic clusters uniformly dispersed thought the random SPAEK polymer backbone matrix. The ionic cluster size was in the range of 5-15nm, which is dependent of the degree of sulfonation. On the oter hand, a large number of smaller ionic clusters (<5nm) and a certain amount of bigger ionic clusters (20-35nm) appeared for block SPAEK membranes. However, the amount of these silver clusters was less than that of random membranes. Instead, the dark colored ionic domains spreading as a cloud-like belt were also observed. These wide ionic domains were well-connected each other by a mass of bigger and smaller ionic clusters together with medium size clusters. This observation was also confirmed by the SAXS analysis. The ionomer peaks in SAXS profiles indicated the presence of large ionic domains for most of polymers. The results showed that the block copolymers exhibited larger size of ionic domains or more clearly phase-separated microstructures with the increase of ionic content and hydrophobic sequence length. Futher, we have studied the properties of the resulted block SPAEK membranes in detail. Then, the relationship between morphology and proton conductivity of block SPAEK membranes was then established according to experimental data.In chapter 4, to obtained more clear structure and more obvious phase sepation, a new series of hydrophobic-hydrophilic multiblock copolymers derived from fluorine terminated poly(arylene ether ketone) as hydrophobic blocks and phenoxide terminated sulfonated poly(arylene ether sulfone) as hydrophilic blocks were successfully synthesized and evaluated for use as proton exchange membranes (PEMs). All the hydrophobic and hydrophilic oligomers were synthesized via molecular-weight controlled step growth polymerization of the monomers. 1H NMR spectra were used as characterization tool to determine the telechelic oligomers'molecular weight and multiblock copolymer's structure. The morphologies of multiblock copolymers were investigated by TEM, which showed they had a clear microphase-separated structure between the hydrophilic domains and hydrophobic domains. All the sulfonated poly(arylene ether sulfone)-b-poly (arylene ether ketone) copolymers can easily be cast into tough membranes and show high thermal stability. Membrane properties including ion exchange capacities (IECs), water uptake and proton conductivities were characterized for the multiblock copolymers and compared with random sulfonated poly(arylene ether)s and other multiblock copolymer membranes at similar ion exchange capacity value. This series of multiblock copolymers showed moderate conductivities up to 0.063 S/cm at 80°C with very low water uptake of 19%. Therefore, they are considered to be promising PEM materials for fuel cells.In chapter 5,highly disulfonated poly( aryl ether ether ketone)s (SPEEK-70) copolymer was synthesized via direct polymerization. To overcome the shortcomings of the SPAEK membrane with high IEC, Poly (amide imide) was blended with SPEEK-70 to improve the methanol resistance and mechanical properties. These blend membranes were characterized as a function of weight fraction of PAI in terms of ion exchange capacity (IEC), water uptake, water desorption, proton conductivity and methanol permeability in detail. Therefore, considering these results, the SPEEK/PAI blend membranes are promising for the usage in DMFC.
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