Synthesis of highly sulfonated poly(arylene ether sulfone)s with sulfonated triptycene pendants for proton exchange membranes

A series of poly(aryl ether sulfone)s containing triptycene groups PES-x-TPD (x refers to molar percentage of TPD) were firstly synthesized through nucleophilic aromatic substitution polycondensation by using 2,5-triptycenediol (TPD), bis(4-hydroxyphenyl) sulfone (BHPS) and 4,4'-difluorodiphenyl sulfone (DFDPS). The sulfonation of copolymers was conducted at room temperature by using a mild sulfonating reagent (98% H2SO4), and the degree of sulfonation was readily and accurately controlled by adjusting the ratio of TPD and BHPS. The structures of PES-x-TPD and SPES-x-TPD were characterized by IR, H-1 NMR and C-13 NMR spectra. These ionomers generally showed high thermal stability and mechanical strength at low humidity regardless of high IEC value. Meanwhile, it is noteworthy that these novel SPES-x-TPD membranes with high IEC value achieved high proton conductivity in a wide range of humidity at 80 degrees C. For example, SPES-60-TPD with the highest IEC value 2.86 mmol/g displays the conductivity of 2.5 x 10(-1) S/cm which is much higher than that of the perfluorinated Nafion membrane (1.1 x 10(-1) S/cm) at 80 degrees C and 94% RH. At 80 degrees C and 34% RH, SPES-60-TPD displays the conductivity of 4.5 x 10(-3) S/cm which is also higher than that of the Nafion membrane (3.0 x 10(-3) S/cm). Microscopic analyses revealed that well-defined phase separated structures and uniform ionic pathway was formed for SPES-45-TPD membrane with the IEC of 2.29 mmol/g. Moreover, a H-2/O-2 fuel cell using the SPES-55-TPD (IEC = 2.68 mmol/g) also showed better performance than that of Nafion 117 at 40 degrees C and 30% RH. (C) 2011 Elsevier Ltd. All rights reserved.