Meta- and para-linked homopolymers bearing 3-methylphenyl (Me) pendent groups were post-sulfonated to create sulfonated poly(ether ether ketone ketone) (SPEEKK) backbone isomers, which are referred to as Me-p-SPEEKK and Me-m-SPEEKK. Their thermal and oxidative stability, mechanical properties, dimensional stability, methanol permeability, and proton conductivity are characterized. Me-p-SPEEKK and Me-m-SPEEKK proton conductivities at 100 degrees C are 116 and 173 mS cm(-1), respectively. Their methanol permeabilities are 3.3-3.9 x 10(-7) cm(2) s(-1), and dimensional swelling at 100 degrees C is 16.4 -17.5%. Me-p-SPEEKK and Me-m-SPEEKK were fabricated into membrane electrode assemblies (MEAs), and electrochemical properties were evaluated within a direct methanol fuel cell (DMFC) and proton exchange membrane fuel cell (PEMFC). When O-2 is used as the oxidant at 80 degrees C and 100% RH, the maximum power density of Me-m-SPEEKK reaches 657 mW cm(-2), which is higher than those of Nafion 115 (552 mW cm(-2)). DMFC performance is 85 mW cm(-2) at 80 degrees C with 2.0 M methanol using Me-p-SPEEKK due to its low MeOH crossover. In general, these electrochemical results are comparable to Nafion. These ionomer properties, combined with a potentially less expensive and scalable polymer manufacturing process, may broaden their potential for many practical applications. (C) 2017 Elsevier B.V. All rights reserved.