Abstract. Synthesis of sulfonated poly (arylene ether sulfone) copolymer by direct copolymerization of 4,4!-bis(4-hydroxyphenyl)valeric acid, benzene 1,4-diol and synthesized sulfonated 4,4!-difluorodiphenylsulfone and its characterization by using FTIR (Fourier Transform Infrared) and NMR (Nuclear Magnetic Resonance) spectroscopic techniques have been performed. The copolymer was subsequently cross-linked with 4, 4!(hexafluoroisopropylidene)diphenol epoxy resin by thermal curing reaction to synthesize crosslinked membranes. The evaluation of properties showed reduction in water and methanol uptake, ion exchange capacity, proton conductivity with simultaneous enhancement in oxidative stability of the crosslinked membranes as compared to pristine membrane. The performance of the membranes has also been evaluated in terms of thermal stability, morphology, mechanical strength and methanol permeability by using Thermo gravimetric analyzer, Differential scanning calorimetery, Atomic force microscopy, XPERT-PRO diffractometer, universal testing machine and diffusion cell, respectively. The results demonstrated that the crosslinked membranes exhibited high thermal stability with phase separation, restrained crystallinity, acceptable mechanical properties and methanol permeability. Therefore, these can serve as promising proton exchange membranes for fuel cell applications.
Sulphonated poly(ether ether ketone) copolymers bearing pendant carboxylic acid (SPEEK-C) have been synthesized via nucleophilic condensation reaction of 4,4-difluorobenzophenone, sulphonated 4,4-difluorobenzophenone and 3,5-dihydroxy benzoic acid. The structure of the sulphonated copolymer was identified from FT-IR and 1 H-NMR spectrum. The pendant carboxylic groups of SPEEK-C were further crosslinked with poly(vinyl alcohol) (PVA) to fabricate the crosslinked (SPEEK/PVA) membranes. The performance of the membranes was evaluated in terms of water uptake, proton conductivity and oxidative stability. The thermal stabilities of the membranes were determined by thermogravimetric analysis and differential scanning calorimetry techniques, whereas the morphological analysis was performed by atomic force microscopy.
A new class of phenolphthalein based poly (arylene ether) multiblock copolymers treated with ionic liquid were synthesized to cast proton conductive membranes. A nucleophilic condensation reaction of 4, 4'-bis (4-hydroxyphenyl) valeric acid based hydrophilic oligomer (M.Wt = 8 kDa) with a series of phenolphthalein based hydrophobic oligomers (M.Wt = 5, 8 and 10 kDa) was carried out to synthesize nano-phase separated multiblock copolymers. Characterization of the synthesized copolymers was carried out using FT-IR, 1 HNMR and gel permeation chromatographic techniques. The fabricated hybrid membranes obtained by the impregnation of ionic liquid (1-butyl-3-methyl-imidazolium tetrafluoroborate (I.L)) in the synthesized multiblock copolymers showed better thermal and oxidative stability. Highly interconnected ionic channels in the hybrid membrane led to improved water uptake and proton conductivity while maintaining the mechanical stability. The Atomic Force Microscopy (AFM) images and Scanning Electron Microscopy (SEM) images showed the hydrophobic-hydrophilic nano-phase separation in the pristine and hybrid multiblock membranes. The challenge of meeting the ever-growing world energy demand has led to the search of renewable power sources with zero-emissions. The recent success of fuel cell driven vehicles using proton exchange membrane fuel cell has encouraged the researchers to look for ways to improve upon the upcoming technology that may change the world. The proton exchange membrane fuel cell (PEMFC) is receiving a lot of attention due to its low operating temperature, high power density and low costs.1-3 The proton exchange membrane (PEMs) is the key component in a PEMFC. Nafion and comparable perfluorosulfonic acid-based membranes are currently the state-of-the-art PEMs, but these suffer from shortcomings such as high permeability, cost, and limited operating temperatures. The difficulty in their synthesis and their environmental incompatibility due to fluorine are other deterrent factors of Nafion membrane. The thermo-oxidative stability, durability and mechanical stability are the other important factors, which affects the PEMFC performance. To overcome these limitations, enormous research efforts are going on for the designing and synthesis of alternative hydrocarbon PEMs. The sulfonated poly (arylene ether) hydrocarbon is attracting widespread interests as PEMs due to its very high thermal and mechanical stability, and good fuel cell performance in the operating temperature conditions. In the last twothree decades, researchers have reported various approaches to prepare the sulfonated hydrocarbon PEMs. [4][5][6] The selection of monomer, direct sulfonation of monomer, post sulfonation of main polymer backbone, crosslinking, blending, grafting, and composites of PEMs have been reported in the literature. [7][8][9][10][11][12] The high proton conductivity of the PEMs can be achieved by increasing the degree of sulfonation, but this ultimately results into water soluble PEMs. Therefore, the other way to impro...
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