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This dissertation describes the past and recent progress in proton exchange membranes (PEM) for fuel cells. In particular the synthesis and characterization of materials for advanced alternative PEM were studied with an emphasis on structure-property and structure-property-performance relationships. The focus has included firstly a one-step synthesis and characterization of 3,3'-disulfonated 4,4'-dichlorodiphenyl sulfone comonomer. The procedure developed is adaptable for industrial-scale commercialization efforts. Secondly, the synthesis of aromatic nitrile containing poly (arylene ether sulfone) random copolymers was demonstrated. Various levels of disulfonation allowed the membrane characteristics to be investigated as a function of the membrane ion exchange capacity. The results favorably compare with the current state-of-the-art (Nafion™), particularly for direct methanol systems (DMFC). Thirdly, the mechanically and thermooxidatively stable copolymer membranes were blended with heteropolyacids producing nanocomposites which have potential in higher temperature fuel cell applications. Lastly, the basic PEM parameters such as water uptake, proton conductivity, and methanol permeabilities were controlled and presented as tunable properties as a function of molecular structure. This was achieved by in-situ control of chemical composition. The direct methanol fuel cell performance (DMFC) was much better than Nafion™. Hydrophobic surface properties of the membranes were improved by partial fluorination which made the Nafion™ bonded electrodes more compatible with the partially fluorinated copolymer membranes. The influence of surface enrichment had two important roles in increasing both initial and long term performance tests. The surface fluorine provided lower contact resistance and lower water uptake. The former was important for the initial tests and the latter provides for better long term performances. A delamination failure mechanism was proposed for the hydrocarbon membrane electrode assemblies (MEA) due to the large difference between water uptake of the catalyst layer and membrane and this was verified by a reduction in high frequency resistance (HFR) for the partially fluorinated systems. This thesis has generated the structure-property and structure-property-performance relationships which will provide direction for the development of next generation (PEM) materials. / Ph. D.

PEM (Proton Exchange Membrane) fuel cell is one of the most important green energy, because it has high energy density, lifetime, small and light.etc advantages. Nafion , the major material for PEM now, However, has some disadvantages such as high cost ($600¡V1000/m2) and limited choices for operation temperature about 25¢J~80¢J. Consequently, there is an increasing interest in the development of alternative ionomer membranes with lower cost, and higher proton conductivity, and that are more easily processed. Here we present polymeric membranes made of sulfonic Poly(arylene ether)s (PAEs) which is achieved by nucleophilic displacement reactions of dihalo or dinitro compounds with alkali metal bisphenolates and direct polymer sulfonation was carried out in heterogeneous media using chlorosulfonic acid as both solvent and sulfonating agent. In our PAEs which has high Tg values about 225¡ã250¢XC depends on the barriers to rotation along the main polymer chain. And weight losses above 500 ¢XC by thermogravimetric (TGA) analysis, indicative of their high thermal stability. After FTIR analysis we preparation sulfonated polymer successfully by using chlorosulfonic acid as sulfonating agent. Thermogravimetric analysis (TGA) studies were carried out to investigate the thermal stability of sulfonated PAEs (Td≈ 500¢XC). The proton conductivity of polymer s(DFB+M3) sulfonated with chlorosulfonic acid about 10-6¡ã10-7S cm-1 .Compared with Nafion membrane measured in the same condition, the conductivity of our membrane is smaller than 3~4 order. In the future, it is possible to improve the conductivity of our membrane with optimization.

Monomer 4,4¡¦¡¦¡¦¡¦-Difluore-3,3¡¦¡¦¡¦¡¦-bis(trifluoromethyl)-2¡¦¡¦,3¡¦¡¦,5¡¦¡¦,6¡¦¡¦-triphenyl (M4) were converted to novel poly(arylene ether)s by nucleophilic displacement reaction with several bisphenols in this study, then we called them : P-A1, P-A2, P-B1, P-B2. These polymers exhibit weightaverage molecular weight (Mw) between 2.2¡Ñ10^4 to 2.2¡Ñ10^5 g/mol. The molecular weight were investigated and confirmed by Mass and GPC. The molecular structures were investigated and confirmed by NMR and FT-IR.Thermal analysis physics studies with these polymers confirmed by Thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC). It is indicated that Td 5% of these polymers were 450¢XC ~ 548¢XC in TGA and Tg of these polymers were 303¢XC ~ 324¢XC in DSC.Besides, these polymers not were observed apparent crystallizing point, so we consider that they are not easy crystallized. Therefore, they could make manufacture in higher temperature and have higher thermal stability.In photophysical property of polymeric thin films, we obtained absorption wavelength that was 232nm ~ 300nm in UV-Vis absorption spectra and excitation wavelength that was 362nm ~ 368nm in PL spectra. Furthermore, the transmission spectra of polymeric thin films showed that visible light transparency were up to 83%. Besides, we used Ellipsometer to measure refractive index(n) that is 1.33 ~ 1.49.In drop shape analysis system, contact angles of the polymeric thin films are more than 109.8¢X. They show that the polymer thin films have low polarity and good hydrophobicity. By above material properties of these polymers, they have high thermal stabilities, high optical transparency, low polarity and good hydrophobicity. These good material properties are doing as a plastic substrate of devices or panel display.

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High temperature, solvent resistant materials which also display good mechanical properties are desired for use as aerospace structural adhesives and polymer matrix/carbon fiber composites. High molecular weight amorphous poly(arylene ether sulfone) thermoplastic materials display many of these desirable characteristics but are deficient in solvent resistance. Previous attempts to prepare poly(arylene ether) based thermosets to improve solvent resistance have been largely unsuccessful due to processiblity issues from the low curing temperature and high glass transition temperature of the thermoset precursor. Incorporation of a high temperature curable (* 350°C) endgroup such as 3-phenylethynylphenol in the synthesis of controlled molecular weight poly(arylene ether sulfone) oligomers has allowed for a large processing window prior to the exothermic cure that forms the desired networks. Control of oligomer molecular weight and backbone structure has allowed for further control of the processing, thermal transitions and adhesive properties of the thermosets. A systematic series of phenylethynyl terminated oligomers derived from either bisphenol A, or wholly aromatic hydroquinone or biphenol has been synthesized and characterized to determine the influence of backbone structure, molecular weight, and endgroup structure on thermoset properties. The features most affected by backbone structure included thermal stability (weight loss behavior) as well as transition temperatures (Tg, Tm), and processing characteristics. Increasing molecular weight of the oligomer produced a decrease in the glass transition temperature of the network and an increase in the adhesive properties of the thermoset. Comparison of the curing behavior of the 3-phenylethynylphenol endcapped materials with other related phenylethynyl terminated compounds led to the synthesis and systematic investigation of the curing behavior of phenylethynyl endcappers in which the electronic environment in relation to the reactive ethynyl carbons was systematically varied. Electron withdrawing groups, eg. sulfone, ketone, imide on the aryl ring para to the acetylene bond enhanced the rate of cure and also appear to improve the lap shear adhesion to suface treated titanium adherands. Discussion of the background, synthesis and characterization are described in this dissertation. / Ph. D.

Poly(arylene ether)s are a well-established class of thermoplastics that are known for their mechanical toughness, thermal stability, and fabrication into membranes. These materials can undergo a myriad of modifications including backbone structure variability, sulfonation, and crosslinking. In this dissertation, structure-property relationships are considered for poly(arylene ether)s with regard to membrane applications for proton exchange and gas separation membranes. All of the proton exchange membranes in this dissertation focus on a disulfonated poly(arylene ether sulfone) based hydrophilic structure to produce hydrophilic-hydrophobic multiblock copolymers. The hydrophobic segments were based upon poly(arylene ether benzonitrile) polymers and copolymers. The oligomers were synthesized and isolated separately, then reacted under mild conditions to form the alternating multiblock copolymers. Structure-property relationships were considered for two different proton exchange membrane applications. One multiblock copolymer system was for H2/air fuel cells, and the other for direct methanol fuel cells (DMFCs). The H2/air fuel cells operate under harsh conditions and varying levels of relative humidity, while the DMFCs operate in an aqueous environment with a methanol-water mixture (typically 0.5-1 M MeOH). Thus two different approaches were taken for the multiblock copolymers. All of the multiblock copolymers were cast into membranes and after annealing resulted in drastically reduced water uptake as compared to random and non-annealed systems. The membranes were characterized with regard to composition, mechanical properties, morphology, water uptake, proton conductivity, and molecular weight. Membranes were also sent to collaborators to elicit the fuel cell performance of the proton exchange membranes. In H2/air fuel cells the approach was to increase charge density by bisphenol choice in the hydrophilic phase. This was performed by switching to a lower molecular weight monomer, hydroquinone, and a monosulfonated hydroquinone. This produced higher charge density in the hydrophilic phase, and the corresponding multiblock copolymer. With increased hydrophilicity the multiblock copolymers showed increased phase separation, proton conductivity, and better performance under relative humidity testing. In the second system for DMFCs, the primary goal was to reduce methanol permeability by bisphenol selection in the hydrophobic phase. This was done with by replacing fifty mole percent of the fluorinated monomer with a series of increasing hydrophobicity bisphenols. Addition of benzylic methyl groups on the bisphenols, was the method undertaken to increase the hydrophobicity. The combination of reduced fluorine content along with the addition of methyl groups resulted in multiblock copolymers with extremely low water uptake and methanol permeability. This allowed for a PEM with better performance than Nafion® in 1M MeOH in DMFC testing. The gas separation membranes presented in this dissertation are based upon poly(arylene ether ketone)s. Two systems were presented: one with a polymer directly synthesized with a bisphenol containing benzylic methyl groups and 4,4'-difluorobenzophenone, and the other a difunctional poly(phenylene oxide) oligomer polymerized with 4,4'-difluorobenzophenone. These systems were crosslinked via UV light through excitation of the ketone group to the triplet state and then hydrogen abstraction from the benzylic methyl. Confirmation of crosslinking was performed via differential scanning calorimetry and infrared spectroscopy. Changes in the glass transitions between crosslinked and non-crosslinked materials were characterized with respect to the concentration of ketones to elicit the effects of crosslink density on the polymers and copolymers. Gas transport properties showed a strong dependence on the ketone percentage as the selectivity was much higher for the homopolymer, while the permeability was higher for the PPO copolymer in the CO2/CH4 and O2/N2 gas pairs. / Ph. D.

The purity of the disulfonated monomer, such as 3,3"-disulfonated-4,4"-dichlorodiphenyl sulfone (SDCDPS), was very important for obtaining high molecular weight copolymers and accurate control of the oligomer's molecular weight. A novel method to characterize the purity of disulfonated monomer, SDCDPS, was developed by using UV-visible spectroscopy. This allowed for utiliziation of the crude SDCDPS directly in the copolymerization to save money, energy, and time. Three series of tert-butylphenyl terminated disulfonated poly(arylene ether sulfone) copolymers (BPSH35, 6FSH35, and 6FSH48) with controlled molecular weightsï¼ Mnï¼ , 20 to 50 kg·mol-1, were successfully prepared by the direct copolymerization method. The molecular weight of the copolymer was controlled by a monofunctional monomer tert-butylphenyl, and characterized by the combination of 1H NMR spectra and modified intrinsic viscosity measurements in NMP with 0.05 M LiBr, which was added to suppress the polyelectrolyte effect. The mechanical properties of the membranes, such as the modulus, strength and elongation at break, were improved by increasing the molecular weights, but water uptake and proton conductivities found insensitive to copolymers" molecular weights. Three series of disulfonated poly(arylene ether ketone) random copolymers have been synthesized and comparatively studied, according to their different chemical structures, for use as proton exchange membranes. The copolymers containing more flexible molecular structures had higher water uptake and proton conductivity than the rigid structures at the same ion exchange capacity. This may be due to the more flexible chemical structures being able to form better phase separated morphology and higher hydration levels. A new hydrophobic-hydrophilic multiblock copolymer has been successfully synthesized based on the careful coupling of a fluorine terminated poly(arylene ether ketone) (6FK) hydrophobic oligomer and a phenoxide terminated disulfonated poly(arylene ether sulfone) (BPSH) hydrophilic oligomer. AFM images and the water diffusion coefficient results confirmed that the multiblock copolymer formed better proton transport channels. This multiblock copolymer showed comparable proton conductivity and fuel cell performance to the Nafion® control and had much better proton transport properties than random ketone copolymers under partially hydrated conditions. This suggested that the multiblock copolymers are promising candidates for proton exchange membranes especially for applications at high temperatures and low relative humidity. / Ph. D.

Poly(arylene ether sulfone)s with dendritic terminal groups were synthesized by step-growth polymerization of two difunctional monomers in the presence of preformed dendritic end-cappers. These polymers were characterized by NMR, SEC, DSC, TGA, melt rheology and tensile tests. The melt viscosities of these polymers in the high frequency region were lower than the control while the stress-strain properties were comparable to those of the control, suggesting that it is possible to reduce the high shear melt viscosities of this type of polymers without affecting the stress-strain properties by introducing bulky dendritic terminal groups. Poly(arylene ether sulfone)s with hyperbranched terminal groups were also synthesized. These polymers were synthesized by reacting fluoro-terminated poly(arylene ether sulfone) chains with an arylene ether ketone AB2 monomer. The terminal groups of these polymers were capped by tert-butylphenol. The results from NMR and SEC showed that multiple tert-butyl units were successfully introduced onto the polymer chains, suggesting that this synthetic method could be useful for introducing multiple functional groups onto the polymer chain ends in fewer synthetic steps than an analogous method using preformed dendritic end-cappers. It was also demonstrated that multiple sulfonated phenols were attached to the terminal groups of polysulfones by this method. A novel cyclohexyl-containing difunctional monomer was prepared and successfully incorporated into poly(arylene ether sulfone) backbones. These polymers were characterized by NMR, SEC, DSC, TGA, DMA and tensile tests and compared to terephthaloyl analogs. Tensile tests and DMA showed the cyclohexyl units impart a higher magnitude of secondary relaxation than the terephthaloyl units while maintaining high modulus, suggesting that these polymers may have higher impact strength than the ones with no cyclohexyl units. / Ph. D.

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