Novel sulfonated polyimides containing multiple cyano groups for polymer electrolyte membranes

• Novel multiple cyano-groups containing polyimides were prepared for PEM applications.
• The properties of the PEMs were carefully characterized.
• The cyano-functionalized SPIs exhibited some attractive properties.
• The CN-SPI membranes exhibited high proton conductivity and low swelling at 100 °C.

Some multiple cyano groups functionalized sulfonated polyimides (CN-SPIs) are prepared derived from a novel CN-diamine monomer for the first time. Meanwhile, some similar SPIs but without cyano groups (Ph-SPIs) are prepared as counterparts for comparison purposes. Both chemical structure and properties of these SPIs are carefully characterized. At 100 °C, proton conductivities of some membranes could reach 0.138–0.146 S cm−1, which are comparative with Nafion. The methanol diffusion coefficients of the membranes are between 1.74 and 5.82 × 10-7 cm2 s−1, which are much more competitive than Nafion 117. It is of interest to find that cyano-functionalized SPIs could possess an excellent combination of low swelling, high proton conductivity and low methanol permeability.

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