Duo Qi

Novel side-chain-type sulfonated diphenyl-based poly(arylene ether sulfone)s with a hydrogen-bonded network as proton exchange membranes

A new bisphenol monomer, 3,3′,5,5′-tetramethoxy-4,4′-dihydroxybiphenyl, was synthesized and copolymerized to prepare diphenyl-based poly(arylene ether sulfone) copolymers containing tetra-methoxy groups (MOPAES). After converting the methoxy group to the reactive hydroxyl group, the resulting side-chain-type sulfonated copolymers (SOPAES) with a hydrogen bonded network were obtained by a sulfobutylation reaction. The copolymers were characterized and confirmed by 1H NMR, FT-IR, thermogravimetric analysis (TGA) and small-angle X-ray scattering. The water uptake, proton and methanol transport properties of the resulting membranes were also determined for fuel cell applications. These SOPAES series membranes showed high proton conductivity in the range of 0.032–0.054 and 0.084–0.142 S cm−1 at 25 and 80 °C under hydrated conditions, respectively. SOPAES-40 (IEC = 1.38 mequiv. g−1) showed comparable proton conductivity with Nafion 117 in the hydrated state. The methanol permeability of these membranes was in the range of 1.58–4.29 × 10−7 cm2 s−1, which is much lower than Nafion (1.55 × 10−6 cm2 s−1). It should be noted that the intra/inter hydrogen bonds formed between sulfonic acid and hydroxyl groups or between hydroxyl and hydroxyl groups improved the mechanical properties and reduced the methanol permeability of the membranes effectively. A combination of suitable proton conductivity, low water uptake, and low methanol crossover for selected SOPAES indicates that they are good candidates as proton exchange membrane materials for fuel cells.

Fully aromatic naphthalene-based sulfonated poly(arylene ether ketone)s with flexible sulfoalkyl groups as polymer electrolyte membranes

A series of sulfonated naphthalene-based poly (arylene ether ketone)s (SNPAEK-xx) with pendant sulfoalkyl groups were prepared by polycondensation of 1,5-bis(4-fluorobenzoyl)-2,6-dimethoxynaphthalene and o-methylhydroquinone, followed by a demethylation and sulfobutylation reaction. The sulfonate degree of SNPAEK-xx could be controlled easily by adjusting the ratio of 1,4-butane sultone to the hydroxyl content in the demethylated polymers. Flexible and tough membranes with reasonably high mechanical strength were prepared. SNPAEK-xx membranes showed a high ionic exchange capacity (IEC) in the range of 1.13 to 2.27 mequiv. g−1, and the highest proton conductivity of 0.191 S cm−1 at 80 °C. They exhibited low methanol permeability in the range of 1.25–10.22 × 10−7 cm2 s−1, which was much lower than that of Nafion 117. Transmission electron microscopy analysis of SNPAEK-xx revealed that they had a more obvious phase separated structure between the hydrophilic side chain and hydrophobic fully aromatic domains at a higher IEC. Combining their high thermal and mechanical stability, high selectivity, lower water swelling ratio, SNPAEK-xx membranes could be promising materials as alternative to Nafion membranes for direct methanol fuel cell applications.

Novel in situ-foaming materials derived from a naphthalene-based poly(arylene ether ketone) containing thermally labile groups

A novel in situ-foaming material was successfully prepared by a naphthalene-based hydroxyl-containing poly(arylene ether ketone) (PAEK) modified with thermally labile tert-butyloxycarbonyl which can decompose and in situ generate CO2 and isobutene as the foaming agents. The structure and thermal properties of the polymers were characterized by using 1H NMR spectra and thermogravimetry coupled time-resolved mass spectrogram (TG/MS). The resulting polymers exhibited relatively high Tg because of the existence of a rigid naphthalene moiety. Then closed microcellular porous membranes with a wide range of expansion ratio (ER) were obtained by a simple thermal treatment from 140 °C to 280 °C for 60 seconds, without using any other physical or chemical foaming agents. The highest ER was 53.98%. This method has never been reported before on high-performance poly(aryl ether) materials. Furthermore, we investigated the relationship between the foaming temperature and the morphology of membranes in detail by using density measurement and scanning electron microscopy (SEM).

Crosslinked tri-side-chain-type sulfonated poly(arylene ether ketones) with enhanced proton conductivity by a Friedel–Crafts acylation reaction

A series of cross-linked sulfonated poly (arylene ether ketones) containing tri-side-chain pendent sulfonic groups (SQNPAEK) were prepared by the Friedel–Crafts acylation reaction in order to solve the problem of high methanol crossover and maintain high proton conductivity for direct methanol fuel cells. For this purpose, sulfonated poly(arylene ether ketones) with pendent carboxylic acid groups were synthesized based on phenolphthalein carboxylic monomers to be used as a macro-crosslinker. The cross-linked membranes showed improved mechanical properties, chemical resistance and oxidative stability. The water uptake and swelling ratio of cross-linked membranes decreased from 57.3% to 18.7%, and from 12.2% to 3.03%, respectively. And the methanol permeability decreased from 0.94 × 10−7 cm2 s−1 to 0.37 × 10−7 cm2 s−1. Regarding the high proton conductivity, it showed enhanced performance over the pristine membrane, up to 0.29 S cm−1. Thus, the cross-linked membranes possessed the better performance implying their potential for practical application in high-energy-density devices.