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.