Fourier Transform Infrared Spectroscopy of Perfluorocarboxylate Polymers

Perfluorocarboxylate polymers in the carboxylic methyl ester, potassium salt, and carboxylic acid forms have been analyzed by Fourier transform infrared (FT-IR) transmission and attenuated total reflectance (ATR) spectroscopy. Band assignments were made for most of the dominant peaks. An absorbance band ratio, comparing the 555 cm^-1 C−F band to the 982 cm^-1 C−O−C ether band, was found to be a direct measure of the equivalent weight of the polymers. In addition, the transition from the methyl ester form to the acid form was determined by examining the 2969 cm^-1 methyl ester band versus the broad ~3200 cm^-1 acid band. Quantitative expressions are presented to enable the computation of equivalent weight and acid content based on FT-IR thin-film absorbance measurements.