Proton-Conducting Membranes from Polyphenylenes Containing Armstrong's Acid

Area of Science:

• Polymer Chemistry
• Materials Science
• Electrochemistry

Background:

• Sulfonated polyphenylenes are key materials for proton exchange membranes (PEMs) in fuel cells.
• Achieving high ion-exchange capacity (IEC) and proton conductivity while maintaining mechanical and chemical stability is a significant challenge.

Purpose of the Study:

• To develop an efficient and economical method for preparing alternating sulfonated polyphenylenes with high IEC.
• To investigate the use of 1,5-naphthalenedisulfonic acid as a building block.
• To enhance polymer properties like solubility and molar mass through protection/deprotection strategies.

Main Methods:

• Suzuki polycondensation utilizing 1,5-naphthalenedisulfonic acid and an all-meta-terphenyl comonomer.
• A protection/deprotection strategy for base-stable neopentyl sulfonates.
• Solution-based deprotection and thermal cross-linking of the synthesized polymers.
• Chemical stability assessment using Fenton's reagent and density functional theory (DFT) calculations.

Main Results:

• Successful synthesis of alternating sulfonated polyphenylenes with high IEC (up to 2.93 mequiv/g) and proton conductivity (138 mS/cm).
• Demonstration that an all-meta-terphenyl comonomer is crucial for achieving high molar masses.
• Thermal cross-linking effectively controlled water uptake (to 50 wt %) while retaining good IEC (2.33 mequiv/g) and conductivity (85 mS/cm).
• DFT calculations indicated high chemical stability of the 1,5-disulfonated naphthalene units against desulfonation.

Conclusions:

• 1,5-naphthalenedisulfonic acid is a viable and cost-effective monomer for high-performance sulfonated polyphenylenes.
• The developed polymer membranes exhibit promising properties for PEM applications, balancing conductivity, IEC, and stability.
• Further optimization of cross-linking is essential for practical application in aqueous environments.