Size-exclusion chromatography of perfluorosulfonated ionomers

Area of Science:

• Polymer Chemistry
• Materials Science
• Analytical Chemistry

Background:

• Perfluorosulfonated ionomers, like Nafion®, are crucial in various applications.
• Accurate determination of their molar mass distribution is essential for understanding material properties.
• Existing characterization methods face challenges with these complex polymers.

Purpose of the Study:

• To develop and validate a size-exclusion chromatography (SEC) method for determining molar mass distributions of perfluorosulfonated ionomers.
• To optimize sample preparation techniques for accurate molecular solutions.
• To establish reliable methods for polymer conformation analysis.

Main Methods:

• Size-exclusion chromatography (SEC) in N,N-dimethylformamide with 0.1 M LiNO(3).
• Optimized autoclaving for aggregate-free molecular solutions.
• Solvent exchange for sample concentration.
• Light scattering and viscometry detection.
• Conformation plots combining molar mass and intrinsic viscosity data.

Main Results:

• The SEC method successfully determined molar mass distributions for three classes of perfluorosulfonated ionomers.
• Conformation plots compensated for refractive index variations, enabling accurate calculations.
• Mark-Houwink-Sakurada constants were derived, allowing molar mass determination without sensitive detectors.
• Analysis revealed unusually free rotation in perfluoroalkane backbones.

Conclusions:

• The developed SEC method is suitable for characterizing perfluorosulfonated ionomers.
• Conformation plots offer a robust approach to overcome detection limitations.
• The findings suggest potential limitations for applying standard excluded volume theories to these ionomers.
• This research provides valuable insights into the structural properties of perfluorosulfonated ionomers.