Wenmeng Zhang,Shaoyun Chen,Dongyang Chen,Zhuoliang Ye
Sterically hindered (S)-1,1′-binaphthyl-2,2′-diol had been successfully copolymerized with 4,4′-sulfonyldiphenol and 4,4′-difluorobenzophenone to yield fibrous poly(arylene ether ketone)s (PAEKs) containing various amounts of binaphthyl unit, which was then selectively and efficiently sulfonated using ClSO3H to yield sulfonated poly(arylene ether ketone)s (SPAEKs) with ion exchange capacities (IECs) ranging from 1.40 to 1.89 mmol·g−1. The chemical structures of the polymers were confirmed by 2D1H–1H COSY NMR and FT-IR. The thermal properties, water uptake, swelling ratio, proton conductivity, oxidative stability and mechanical properties of SPAEKs were investigated in detail. It was found that the conjugated but non-coplanar structure of binaphthyl unit endorsed excellent solubility and film-forming capability to SPAEKs. The SPAEK-50 with an IEC of 1.89 mmol·g−1exhibited a proton conductivity of 102 mS·cm−1at 30 °C, much higher than that of the state-of-the-art Nafion N212 membrane and those of many previously reported aromatic analogs, which may be attributed to the likely large intrinsic free volume of SPAEKs created by the highly twisted chain structures and the desirable microscopic morphology. Along with the remarkable water affinity, thermal stabilities and mechanical properties, the SPAEKs were demonstrated to be promising proton exchange membrane (PEM) candidates for potential membrane separations.Keywords:proton exchange membranes;condensation polymerization;post-sulfonation;binaphthyl;film-forming capability
A series of multiblock sulfonated poly(arylene ether sulfone)s (SPAES) with various block lengths and predictable ion exchange capacity were synthesized from 4,4′-difluorodiphenyl sulfone, 4,4′-dihydrodiphenyl sulfone and 4,4′-biphenol by one-pot and two-pot polymerization. 1 H-NMR and FTIR spectra confirmed the structure that sulfonic acid groups were introduced precisely on the poly(arylene ether sulfone)s by post-sulfonation which resulted in controllable sulfonation degree. The proton exchange membranes (PEMs)-based SPAES displayed excellent dimensional, thermal, antioxidant stability, proton conductivity and mechanical properties (maximum tensile stress >35 MPa). Thermogravimetric analysis indicated the prepared SPAES began to degrade above 310 °C. The effects of polymerization processes, those were, one-pot hydrophobic segment process, one-pot hydrophilic segment process and two-pot process, on the properties of polymers were investigated. The proton conductivity and microphase separation of SPAES PEMs increased in order of those prepared by one-pot hydrophobic segment process, two-pot process and one-pot hydrophilic segment process. The highest conductivities of SPAES synthesized by the above processes under 80 °C and 100% relative humidity were 213 (MS4), 297 (MB3) and 360 mS·cm −1 (MQ2), respectively.
Dongyang Chen,Shuanjin Wang,Min Xiao,Yuezhong Meng,Allan S. Hay
A novel dihydroxyl monomer bearing 18 electron rich phenyl rings were synthesized and polymerized with other monomers bearing electron deficient phenyl rings to give dense and selective sites in macromolecules for post-sulfonation, which was successfully conducted in ClSO3H/CH2Cl2 solution at room temperature in a subsequential step. The chemical structures were confirmed by 1H NMR and FT-IR spectra. The ionic exchange capacity (IEC) was controlled to be from 0.65 to 1.21 mequiv g−1 to afford considerable proton conductivity. Distinct phase separation was observed in the resulting membranes from SAXS profiles. The SPAEK-5 with an IEC of 1.21 mequiv g−1 gave better proton conductivity than Nafion 117 at all tested temperatures under 100% relative humidity. The membranes exhibited an exceeding stability when immersing in Fenton's reagent (3 wt.% H2O2 + 2 ppm FeSO4) at 80 °C. These properties make them promising candidates for electrochemical applications.
A carbon-carbon linked polyaromatic electrolyte was designed and synthesized for proton exchange membranes. The facile synthesis consists of a metal-free Friedel-Crafts polymerization and a direct post-sulfonation. To prevent the random sulfonation, the trifluorobuanone monomer was incorporated as a spacer to sterically confine the sulfonated area. Hydrophobic/hydrophilic separation was observed in the polymer's microstructure. The membrane (ion exchange capacity = 1.88 mmolg −1 ) displayed low water swelling (area swelling = 38.0% at 80 °C) at a slightly higher proton conductivity than Nafion 212. Tensile strength of 39.3 MPa and elongation at break of 67.0% were confirmed by stress-strain measurements. The membrane electrode assembly afforded an electrolyzing performance of 4.6 A cm −2 @2.0 V while Nafion 212 was 3.6 A cm −2 @2.0 V under the same testing conditions. The 45 μm film exhibited better stability than Nafion 212 (∼50 μm) both in the preliminary in-situ cyclic accelerated stress test and the 800-h galvanostatic evaluation. The degradation rate of our thin membrane in the 800-h test was comparable to that of Nafion 115 (∼125 μm).
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