Sulfonated polyimides containing triphenylphosphine oxide for proton exchange membranes

• Triphenylphosphine oxide containing sulfonated polyimides (SPIs) was synthesized.
• The SPIs showed good oxidative and hydrolytic stability and high proton conductivity.
• TEM analysis revealed well separated morphology of the SPIs.

A series of sulfonated co-polyimides (co-SPI) were prepared by one pot polycondensation reaction of a combination of diamines namely; 4,4′-diaminostilbene-2,2′-disulfonic acid (DSDSA) and prepared non-sulfonated diamine (DATPPO) containing triphenylphosphine oxide with 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA). All these soluble co-SPI gave flexible membranes with high thermal stability and showed good mechanical property. Transmission electron microscopy (TEM) analysis revealed the microphase separated morphology with well-dispersed hydrophilic (cluster size in the range of 5–55 nm) domains. The co-SPI membranes showed high oxidative and hydrolytic stability with higher proton conductivity. All these co-SPI membranes exhibited low water uptake and swelling ratio. The co-SPI membrane TPPO-60 (60% degree of sulfonation) with IECW = 1.84 mequiv g−1 showed high proton conductivity (99 mS cm−1 at 80 °C and 107 mS cm−1 at 90 °C) in water with high oxidative (20 h) and hydrolytic stability (only 5% degradation in 24 h).

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