Astonishing synergetic effect of proton conducting between phosphonic acid groups and triazolyl groups tethered simultaneously on poly(ether sulfone) backbone

Abstract

A novel phosphonic acid and triazolyl functionalized poly(ether sulfone) (PES-TriPA) containing simultaneously phosphonic acid and triazolyl side groups is synthesized. The PES-TriPA is prepared by polycondensation of phosphonated bisphenol (PBP) and 3,3′-diethynyl-4,4′-difluorodiphenylsulfone, followed by click reaction to introduce triazolyl groups and hydrolysis to free phosphonic acid groups. Phosphonic acid functionalized poly(ether sulfone) (PES-PA) and triazolyl functionalized poly(ether sulfone) (PES-Tri) are also synthesized for comparison with PES-TriPA. The proton conducting polymers are hot-pressed into proton exchange membranes, and the membrane morphologies, proton conductivities, oxidation and thermal stabilities, water uptakes and methanol permeabilities are characterized. PES-TriPA exhibits more excellent comprehensive properties in comparison with PES-PA and PES-Tri. At 100 °C and 90% relative humidity (RH), the proton conductivity of PES-TriPA reaches 113.0 mS cm−1, in comparison with 55.7 mS cm−1 for PES-PA and 4.3 mS cm−1 for PES-Tri. PES-TriPA also shows better oxidation stability with 95.7% weight left after Fenton's test at 80 °C for 120 h, while only 68.7% left for PES-PA and 75.7% left for PES-Tri. In addition, PES-TriPA exhibits favorable thermal stability and water uptake compared with PES-PA and PES-Tri. Moreover, the methanol permeability of PES-TriPA is only 0.24 × 10−8 cm2 s−1, which is lower than these of PES-PA and PES-Tri with 0.77 × 10−8 cm2 s−1 and 1.20 × 10−8 cm2 s−1, respectively. These superior characteristics are attributed to the synergetic effect between the phosphonic acid groups and triazolyl groups caused by the intermolecular hydrogen bonding interaction throughout the PES-TriPA acid-base amphoteric polymer.