High performance engineering materials, poly(arylene ether)s, having very good mechanical properties, excellent oxidative and hydrolytic stability are promising candidates for alternative materials used in the field of Proton Exchange Membrane Fuel Cells (PEMFCs) and Reverse Osmosis (RO) applications. In particular, wholly aromatic sulfonated poly(arylene ether sulfone)s are of considerable interest in the field of PEMFCs and RO, due to their affordability, high Tg, and the ease of sulfonation. Proton exchange membrane fuels cells (PEMFCs) are one of the primary alternate source of energy. A Proton exchange membrane (PEM) is one of the key component in a PEMFC and it needs to have good proton conductivity under partially humidified conditions. One of the strategies to increase proton conductivity under partially RH conditions is to synthesize hydrophobic-hydrophilic multiblock copolymers with high Ion exchange capacity (IEC) values to ensure sufficient ion channel size. In this thesis two multiblock systems were synthesized incorporating trisulfonated hydrophilic oligomers and were characterized in the first two chapters of the thesis. The first multiblock system incorporated a non-fluorinated biphenol-based hydrophobic block. The second study was focused on synthesizing a fluorinated benzonitrile-based hydrophobic block. A fluorinated monomer was incorporated with the aim to improve phase separation which might lead to increased performance under partially humidified conditions. The third study featured synthesis and characterization of a novel hydroquinone-based random copolymer system precursor, which after post-sulfonation, shall form mono-sulfonated polysulfone materials with potential applications in reverse osmosis. The ratio of the amount of hydroquinone incorporated in the copolymer were varied during the synthesis of the precursor to facilitate control over the post-sulfonation process. The simple and low cost process of post-sulfonating the random copolymer enables the precursor to be a promising material to be used in the reverse osmosis application. / Master of Science

No description available.

Proton exchange membrane fuels cells (PEMFCs) are one of the primary alternatives to internal combustion engines. The key component is the proton exchange membrane, or PEM, which should meet a number of requirements, including good proton conductivity under partially humidified conditions. A number of alternative PEMs have been synthesized by copolymerizing various aromatic comonomers, but the smaller ion channels prohibit rapid proton transport under partially hydrated conditions. One solution has been to synthesize multiblock copolymers from hydrophilic and hydrophobic oligomers to ensure sufficient ion channel size. Four multiblock systems were synthesized from hydrophobic and hydrophilic oligomers and were characterized in this thesis. The first multiblock system incorporated a partially fluorinated monomer into the hydrophobic block, to improve phase separation and performance under partially humidified conditions. The second study was focused on phase separation and structure-property relationships as a function of casting conditions of a biphenol-based multiblock series. The third study featured a novel hydroquinone-based hydrophilic oligomer in the multiblock copolymer, which showed the promise of a higher ionic density, degree of phase separation and proton conductivity values. The fourth study in this thesis entailed the comparison of a block copolymer produced with two distinct synthetic routes: the multiblock synthesis from separate oligomers as previously published in the literature, and a segmented route seeking to achieve comparable structure-property relationships with the same monomers, but using a simpler synthetic route. The two block copolymer series were found to be comparable in their structure-property relationships. / Master of Science

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Polydimethylsiloxane–polyester (PDMS-PES) copolymers produce materials which have enhanced properties and take advantage of the unique properties of the two very dissimilar components. The dissimilar nature of the components results in these types of materials typically having complex morphologies in the solid state as a result of phase segregation. When the polyester component is crystallisable, an even richer variation in morphology can be expected. The chain structure of the copolymer in terms of the distribution of the various segments along the chain and the variation in the composition also has a dramatic impact on the solid state morphology. In this study, two different types of polyesters were used to synthesise five series of PDMS-PES segmented copolymers and one series of PDMS-PES branched copolymer. The two polyester segments selected were polybutyleneadipate (PBA) and polybuthylenecyclohexancarboxylate (PBCH). The copolymers were synthesised via polycondensation in the melt state. Insights on many variations in the PDMS-PES copolymer synthesis are given. The copolymer series synthesized gave systematic series where the influence of the polyester type, chain architecture, bulk composition, block length, crystallinity and processing condition on the bulk and surface morphology could be studied. The remarkable variations in the properties of the copolymer were attributed to the differences in the copolymers morphology in terms of the microphase segregation, crystallization and the free volume properties. These variations were also found to alter the nature of the surface compositions and the related surface properties. Multiphase morphology exhibited in all the PDMS-PES copolymers and the type of morphology observed was dependent on PDMS contents, PDMS segment length and the degree of branching. Three types of morphology were observed: spherical micro-domains of PDMS in a matrix of PES, bicontinuous double diamond type morphology, and spherical micro-domains of PES in a matrix of PDMS. Spherical domains of the PDMS were also observed for low PDMS content copolymers between the crystalline polyester lamellae. The complexity of the PDMS-PBCH copolymer morphology was further investigated, using an extensive set of experimental data that has been drawn together with using positron annihilation lifetime spectroscopy (PALS) and developing and applying a new type of hyphenated technique between fractionation (chromatography) and microscopy (atomic force microscopy) techniques. The outcome has provided a unique perspective regarding the complexity of the PDMS-PBCH copolymer morphology, which is believed to provide basis for a theoretical structure-properties relationship in this fascinating class of thermoplastic material. / AFRIKAANSE OPSOMMING: Polidimetielsiloksaan–poliëster (PDMS–PES) kopolimere lewer verbindings met goeie eienskappe en trek voordeel uit die unieke eienskappe van die twee baie verskillende komponente. Aangesien die aard van hierdie twee verbindings baie verskil het hulle ‘n gekompliseerde morfologie in die vastetoestand as gevolg van faseskeiding. Wanneer die poliëster komponent kristalliseerbaar is kan ‘n nog ryker variasie in morfologie verwag word. Die kettingstruktuur van die kopolimere in terme van die verspreiding van die verskillende segmente al langs die ketting en die variasie in samestelling, het ook ‘n groot invloed op die vastetoestandmorfologie. In hierdie studie is twee verskillende tipes poliëster gebruik om vyf reekse PDMS–PES gesegmenteerde kopolimere en een reeks vertakte PDMS–PES kopolimere te berei. Die twee poliëstersegmente is polibutileenadipaat (PBA) en polibutileensikloheksaankarboksilaat (PBCH). Die kopolimere is berei deur middel van polikondensasie in die smeltfase. Inligting aangaande verskeie faktore in the bereiding van die PDMS–PES kopolimere is ingewin. Die reekse kopolimere wat berei is, het dit moontlik gemaak om die invloed van die tipe poliëster, kettingargitektuur, grootmaatsamestelling, bloklengte, kristalliniteit en reaksiekondisies op die oppervlakte en interne morfologie te bestudeer. Die opmerklike verskille in the eienskappe van die kopolimere word toegeskryf aan die verskille in die kopolimeermorfologie in terme van die mikrofaseskeiding, kristalliniteit en vryevolume eienskappe. Hierdie verskille het ook veranderings in die oppervlakte samestellings en verwante oppervlakte eienskappe teweeggebring. Multifase morfologie, in alle PDMS–PES kopolimere en die tipe morfologie wat waargeneem is, is afhanklik van die PDMS inhoud, die PDMS segmentlengte en die graad van vertakking. Drie tipes morfologie is waargeneem: sferiese mikro-gebiede van PDMS in ‘n PES matriks, ‘n bikontinueerlike dubbele-diamant tipe en sferiese mikro-gebiede van PES in ‘n PDMS matriks. Sferiese gebiede van die PDMS is ook waargeneem in kopolimere met ‘n lae PDMS inhoud tussen die kristallyne poliëster lae. Die kompleksiteit van die PDMS–PBCH kopolimeermorfologie is verder ondersoek deur gebruik te maak van ‘n wye reeks eksperimentele data afkomstig van positronvernietigingsleeftydspektroskopie (PALS), gevolg deur die ontwikkeling en toepassing van ‘n nuwe soort gekoppelde tegniek – tussen fraksionering (chromatografie) en mikroskopie (atoomkragmikroskopie) tegnieke. Die resultate het ‘n unieke perspektief gegee wat betref die kompleksiteit van die PDMS–PBCH kopolimeermorfologie en dien as ‘n basis vir die teoretiese struktuur–eienskapverwantskap van hierdie interessante klas termoplastiese materiale.

Proton exchange membrane fuel cells (PEMFCs) have been extensively studied as clean, sustainable and efficient power sources for electric vehicles, and portable and residential power sources. As one of the key components in PEMFC system, proton exchange membranes (PEMs) act as the electrolyte that transfers protons from the anode to the cathode. The state-of-art commercial PEM materials are typically based on perfluorinated sulfonic acid containing ionomers (PFSAs), represented by DuPont's Nafion®. Despite their good chemical stability and proton conductivity at high relative humidity (RH) and low temperature, several major drawbacks have been observed on PFSAs, such as high cost, high fuel permeability, insufficient thermo-mechanical properties above 80°C, and low proton conductivity at low RH levels. Therefore the challenge lies in developing alternative PEMs which feature associated ionic domains at low hydration levels. Nanophase separated hydrophilic-hydrophobic block copolymer ionomers are believed to be desirable for this purpose Three series of hydrophobic/hydrophillic, partially fluorinated/sulfonated multiblock copolymers were synthesized and characterized in this thesis. The hydrophilic blocks were based upon the nucleophilic step polymerization of 3, 3′-disulfonated, 4, 4′-dichlorodiphenyl sulfone (SDCDPS) with an excess 4, 4′-biphenol (BP) to afford phenoxide endgroups. The partially fluorinated hydrophobic blocks were largely based on 4, 4′-hexafluoroisopropylidenediphenol (6F-BPA) and various difluoro monomers (excess). These copolymers were obtained through moderate temperature (~130-150°C) coupling reactions, which minimize the ether-ether interchanges between hydrophobic and hydrophilic telechelic oligomers via a nucleophilic aromatic substitution mechanism. The copolymers were obtained in high molecular weights and were solvent cast into tough membranes, which had nanophase separated hydrophilic and hydrophobic regions. The performance and structure-property relationships of these materials were studied and compared to random copolymer systems. NMR results supported that the multiblock sequence had been achieved. They displayed superior proton conductivity, due to ionic, proton conducting channels formed through the self-assembly of the sulfonated blocks. The nano-phase separated morphologies of the copolymer membranes were studied and confirmed by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Through control of a variety of parameters, including ion exchange capacity and sequence lengths, performances as high, or even higher than those of the state-of-the-art PEM, Nafion®, were achieved. Another series of semi-crystalline hydrophobic poly(ether ether ketone)-hydrophilic sulfonated poly(arylene ether sulfone) (PEEK-BPSH100) multiblock copolymers was first synthesized and characterized. However due to their semi-crystalline structure, PEEK blocks are insoluble in most organic solvents at relatively low reaction temperatures, which prevents the coupling reaction between PEEK and BPS100. In order to facilitate the synthesis and processing, removable bulky ketimine was introduced to synthesize amorphous pre-oligomers poly(ether ether ketimine) (PEEKt). The synthetic procedure first involves the synthesis of hydrophobic poly(ether ether ketimine)-hydrophilic sulfonated poly(arylene ether sulfone) (PEEKt-BPS100) multiblock pre-copolymers via coupling reactions between phenoxide terminated hydrophilic BPS100 and fluorine terminated hydrophobic PEEKt blocks. The membranes cast from PEEKt-BPS100 were boiled in 0.5M sulfuric acid water solution to hydrolyze the amorphous PEEKt blocks to semi-crystalline PEEK blocks and acidify BPS100 blocks to BPSH100 blocks simultaneously. FT-IR spectra clearly showed the successful hydrolysis and acidification. The proton conductivity, water uptake and other membrane properties of the acidified semi-crystalline PEEK-BPSH100 membranes were then evaluated and compared with those of the state-of-the-art PEM, Nafion®. / Ph. D.

Hydrophilic/hydrophobic block copolymers as proton exchange membranes (PEMs) has become an emerging area of research in recent years. Three series of hydrophilic/hydrophobic, fluorinated/sulfonated multiblock copolymers were synthesized and characterized in this thesis. These copolymers were obtained through moderate temperature (~100°C) coupling reactions, which minimize the ether-ether interchanges between hydrophobic and hydrophilic telechelic oligomers via a nucleophilic aromatic substitution mechanism. The hydrophilic blocks were based on the nucleophilic step polymerization of 3,3′-disulfonated, 4,4′-dichlorodiphenyl sulfone with an excess 4,4′-biphenol to afford phenoxide endgroups. The hydrophobic (fluorinated) blocks were largely based on decafluoro biphenyl (excess) and various bisphenols. The copolymers were obtained in high molecular weights and were solvent cast into tough membranes, which had nanophase separated hydrophilic and hydrophobic regions. The performance and structure-property relationships of these materials were studied and compared to random copolymer systems. NMR results supported that the multiblock sequence had been achieved. They displayed superior proton conductivity, due to the ionic proton conducting channels formed through the self-assembly of the sulfonated blocks. The nano-phase separated morphologies of the copolymer membranes were studied and confirmed by atomic force microscopy. Through control of a variety of parameters, including ion exchange capacity and sequence lengths, performances as high, or even higher than those of the state-of-the-art PEM, Nafion, were achieved. / Ph. D.

Poly(arylene ether sulfone)s (PAES) are important commercial polymers and have been extensively studied due to their excellent thermal and mechanical properties. However, some applications are still limited when good solvent resistance and low thermal expansion coefficient are required. There has been a continuous interest in developing new PAES based on new monomers or polymer modifications to obtain new properties or to enhance existing properties. In this dissertation, the synthesis, characterization and structure-property relationship of new 1,4-cyclohexylene ring containing PAESs were comprehensively studied. Different polymerization techniques were used to synthesize polymers with different segmental lengths. The monomer, 4,4'-[trans-1,4-cyclohexanebis(methylene)] bisphenol (CMB), was synthesized and fully characterized. Based on 4,4′-dihydroxy-p-terphenyl (DHTP), 4,4′-dihydroxybiphenyl (DHBP) and the CMB monomer, homopolymer and random copolymers of PAES were prepared with high molecular weights and high glass transition temperatures. Dynamic mechanical analysis (DMA) on these polymers showed multiple sub-Tg relaxations. A large increase in the ultimate elongation was obtained with the CMB and DHTP containing sample, which could be due to the strong sub-Tg relaxations observed from the DMA results. A series of four acid chloride monomers were synthesized and polymerized with phenol terminated PAES oligomers. Solution polymerization and pseudo-interfacial polymerization techniques were used to prepare both bisphenol-A (bis-A) based and DHBP based PAES oligomers. With the incorporation of the trans-1,4-cyclohexylene units, decreases in the glass transition temperatures were observed from both the bis-A based and the DHBP based polymers. However, melting transitions were only observed in the DHBP based trans-1,4-cyclohexylene containing PAESs. Crystallinity was confirmed by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). A mechanical property study of the high molecular weight trans-1,4-cyclohexylene containing polymer samples showed moderate ultimate elongation enhancements. A series of PAES-polyester multiblock copolymers were synthesized with both solution method and melt polymerization. In the solution method, phenol terminated PAES oligomers and the acid chloride terminated poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) oligomers were presynthesized and coupled in solution. The molecular weights of the polymer products obtained from the solution method were limited by solubility issues. Melt phase polymerization was employed to obtain high molecular weight polymers. Hydroxy ethoxy terminated PAES oligomers were synthesized and polymerized with 1,4-cyclohexanedimethanol (CHDM) and dimethyl terephthalate (DMT) in the melt. Polymers with high molecular weights were obtained. Tensile test results suggested that the mechanical properties of these polymers were dominated by the PAES components with polyester contents up to 20 wt%. Melting transitions were observed from polymers with higher polyester contents, and these polymers exhibited limited solubility in common organic solvents. / Ph. D.

Ces travaux ont été dédiés à la synthèse et la caractérisation de nouveaux ionomères aromatiques à blocs pour les PEMFC. Les blocs hydrophiles sont constitués par des polysufones fonctionnalisés par des chaînes latérales alkylperfluorosulfoniques, les blocs hydrophobes sont des polysulfones partiellement fluorés. La synthèse du squelette polymère a été réalisée par de polycondensation, les fonctions ioniques ont été greffées par un couplage d'Ullmann. Trois ionomères de différentes capacités d'échange ionique ont été synthétisés en modulant les longueurs des blocs porteurs des fonctions alkylperflurosulfoniques. Ces ionomères ont été mis en œuvre sous forme de membranes par coulée-évaporation. L'impact du solvant d'élaboration et de la structure chimique des ionomères sur la morphologie et les propriétés intrinsèques des membranes ont été largement étudiés. Le solvant de mise en œuvre de la membrane a un effet spectaculaire sur l'organisation des chaînes polymères à l'échelle nanométrique. Les études par diffusion des neutrons aux petits angles montrent que la morphologie des membranes est dépendante de la longueur des blocs hydrophiles. Les propriétés thermomécaniques et les conductivités protoniques des membranes ionomères aromatiques sont supérieures au Nafion, au-delà de 60°C, ce qui les rend prometteuses pour l'application PEMFC opérant à plus de 100°C. / The purpose of this work was the synthesis and characterization of new aromatic ionomers for PEMFC. The ionomers are based on block copolymers containing hydrophilic blocks, functionalised with a perfluorinated acid, and hydrophobic blocks containing partially perfluorinated aromatic rings. The polymer main chain was performed by polycondensation reaction. The acidic functions were grafted onto the polymer in two steps: bromination and coupling Ullman reaction. Different copolymers with different lengths of hydrophilic block were synthetized. The membranes were obtained by casting, the impact of the solvent nature and Ionomer structure on the membrane morphology and properties was studied. The solvent has a strong impact on the membrane structuration at nanometric scale. By small angle neutrons scattering, we showed that the membrane morphology is depending on hydrophilic bloc length. The mechanical strengths and the conductivities of aromatic ionomer membranes are higher that the Nafion above 60°C that make them promising for PEMFC working at temperature higher than 100°C.

Nanophase-separated hydrophilic-hydrophobic multiblock copolymers are promising proton exchange membrane (PEM) materials due to their ability to form various morphological structures which enhance transport. Four arylene chlorides monomers (2,5-Dichlorobenzophenone and its derivatives) were first successfully synthesized from aluminum chloride-catalyzed, Friedel-Crafts acylation of benzene and various aromatic compounds with 2,5-dichlorobenzoyl chloride. These monomers were then polymerized via Ni (0)-catalyzed coupling reaction to form various high molecular weight substituted poly(2,5-benzophenone)s. Great care must be taken to achieve anhydrous and inert conditions during the reaction. A series of poly(2,5-benzophenone) activated aryl fluoride telechelic oligomers with different block molecular weights were then successfully synthesized by Ni (0)- catalyzed coupling of 2,5-dichloro-benzophenone and the end-capping agent 4-chloro-4'-fluorobenzophenone or 4-chlorophenly-4′-fluorophenyl sulfone. The molecular weights of these oligomers were readily controlled by altering the amount of end-capping agent. These telechelic oligomers (hydrophobic) were then copolymerized with phenoxide terminated disulfonated poly (arylene ether sulfone)s (hydrophilic) by nucleophilic aromatic substitution to form novel hydrophilic-hydrophobic multiblock copolymers. A series of novel multiblock copolymers with number average block lengths ranging from 3,000 to 10,000 g/mol were successfully synthesized. Two separate Tgs were observed via DSC in the transparent multiblock copolymer films when each block length was longer than 6,000 g/mol (6k). Tapping mode atomic force microscopy (AFM) also showed clear nanophase separation between the hydrophilic and hydrophobic domains and the influence of block length, as one increased from 6k to 10k. Transparent and creasable films were solvent-cast and exhibited good proton conductivity and low water uptake. These PAES-PBP multiblock copolymers also showed much less relative humidity (RH) dependence than random sulfonated aromatic copolymers BPSH 35 in proton conductivity, with values that were almost the same as Nafion with decreasing RHs. This phenomenon lies in the fact that this multiblock copolymer possesses a unique co-continuous nanophase separated morphology, as confirmed by AFM and DSC data. Since this unique co-continuous morphology (interconnected channels and networks) dramatically facilitates the proton transport (increase the diffusion coefficient of water), improved proton conductivity under partially hydrated conditions becomes feasible. These multiblock copolymers are therefore considered to be very promising candidates for high temperature proton exchange membranes in fuel cells. / Ph. D.