Perfluorocarboxylate polymer

Membrane cells are the state of the art chlor-alkah technology as of this writing. There are about 14 different membrane cell designs in use worldwide (34). The operating characteristics of some membrane cells are given in Table 3. The membranes are perfluorosulfonate polymers, perfluorocarboxylate polymers, and combinations of these polymers. Membranes are usually reinforced with a Teflon fabric. Many improvements have been made in membrane cell designs to accommodate membranes in recent years (35,36). 

Thus all successful chlor-alkali membranes currently employ a perfluorocarboxylate polymer to lower the rate of hydroxide ion transport. The sulfonate portion of some of these membranes is present mainly to add strength to the thinner carboxylate barrier layer. Fabric backing is also used in some cases to improve physical strength. 

This chapter summarizes the preparation and the fabrication of perfluorocarboxylate polymers and their fundamental properties including those of the ionized salt-type membranes. The application of Flemion in chlor-alkali electrolysis is also described. 

Perfluorocarboxylate polymers were prepared by copolymerization of tetrafluoroethylene and carboxylated perfluorovinyl ether. 

H. Ukihashi and M. Yamabe, Perfluorocarboxylate polymer membranes, Perfluorinated Ionomer Membranes, ACS Symposium Series, ed. A. Eisenberg and H.L. Yeager, American Chemical Society, Washington DC, 1982, Vol. 180, p. 427. 

R. Wodzki and J. Nowaczyk, Membrane transport of organics. I. Sorption and permeation of carboxylic acids in perfluorosulfonic and perfluorocarboxylic polymer membranes, J. Appl. Polym. Sci., 1997, 63, 355-362. 

Perfluorocarboxylate polymers in the carboxylic methyl ester, potassium salt and carboxylic acid forms were analysed by FTIR transmission and ATR spectroscopies. Band assignments were made for most of the dominant peaks. An absorbance band ratio, comparing the 555/cm C-F band to the 982/cm 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 methyl ester band versus the broad 3200/cm band. Quantitative expressions were presented for use in the computation of equivalent weight and acid content based on the FTIR thin film absorbance measurements. The technique used provided a direct measure of the trade-off... 

Many experimental techniques have been used to examine the detailed structure of perfluorinated polymeric membranes. These include transmission electron microscopy [23], small angle X-ray scattering [24], Infra Red spectroscopy [25,26], neutron diffraction [27], Nuclear Magnetic Resonance [26,28], mechanical and dielectric relaxation [25,29], X-ray diffraction, and transport measurements. All these methods show convincing evidence for the existence of two phases in the perfluorosulfonate and perfluorocarboxylate polymers. One phase has crystallinity and a structure close to that of polytetrafluoroethylene (PTFE), and the other is an aqueous phase containing ionic groups. 

Perusich, S. A. 2000. Fourier transform infrared spectroscopy of perfluorocarboxylate polymers. Macromolecules 33 3431-3440. 

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