Perfluorocarboxylic acid polymer

Influence of Electrolysis Conditions. Among the various electrolysis conditions, brine purity has the most significant effect on the life of the membranes. The presence of a small amount of multivalent cations leads to formation of metal hydroxide deposits in the membrane, and thus causes a decrease in current efficiency, an increase in cell voltage, and damage to the polymer structure of the membrane. With perfluorocarboxylic acid membrane, the presence of more than 1 ppm of calcium ion will begin to cause these problems in a very short period (1 - 8). To obtain stable current efficiency and cell voltage, it is therefore essential to establish effective brine purification methods. 

The molecular structure of a conventional polymer used for a PFSA membrane is shown in Fig. 1. Membranes registered as Nafion (DuPont), Flemion , (Asahi Glass), and Aciplex (Asahi Chemical) have been commercialized for brine electrolysis and they are used in the form of alkali metal salt. Figure 4 shows a schematic illustration of a membrane for chlor-alkali electrolysis. The PFSA layer is laminated with a thin perfluorocarboxylic acid layer, and both sides of the composite membrane are hydrophilized to avoid the sticking of evolved hydrogen and chlorine. The membrane is reinforced with PTFE cloth. The technology was applied to PEFC membranes with thickness of over 50 xm [14]. 

Poly(l,l-dihydroperfluoroalkyl acrylates) are obtained in the following manner Aliphatic carboxylic acids are fluorinated electrochemically. The resulting perfluorocarboxylic acids, CF3(Cp2)jcCOOH, are hydrogenated in the form of their acyl chlorides or esters, and the resulting 1,1-dihydroper-fluoroalcohols are esterified with acrylyl chloride. The monomers are polymerized with K2S2O8 in aqueous emulsion. Oil-resistant elastomers result from vulcanization of these polymers with sulfur/triethylene tetramine. Poly(l,l-dihydroperfluorobutyl acrylate) and poly(3-perfluoromethoxy-l,l-dihydroperfluoropropyl acrylate) are commercially available. 

Possibly one of the most complex deliberately designed of all polymer products is the family of membranes described by Seko for the selective passage of sodium (Na+) ions and repulsion of hydroxide ions in a chlorine cell. These perfluorocarboxylic acid membranes are claimed to represent an improvement on the Dupont Nafion class of perfluorosulphonic membranes designed for the same purpose, in that CF/OH" segregation is practically complete. Industrially, the implications for chlorine and caustic soda technology are profound. 

Ionic polymers usually used for the IPMC are perfluorosulfonic acid or perfulorocar-boxylic acid polymers, of which the typical chemical structures are shown in Figure 5.2 [10]. Commercially available products of thin films made from perfluorosulfonie acid can be obtained from E.I. Dupont de Nemours Co. (Nafion). Several other companies supply similar compounds. Asahi Glass Co. produces perfluorocarboxylic acid type (Hemion). 

K.Onishi et al. proposed a tube of IPMC as a microactuator for active catheters [21]. Their suggested device is a perfluorocarboxylic acid (ion exchange polymer) tube... 

Methods of preparing the polymers have been reviewed (Young, 1972) but no one method is at present wholly satisfactory. Probably the most thoroughly studied method involves the ring closure of poly(imidoylamidine) with, for example, the anhydride of a perfluorocarboxylic acid. 

Multilayer membranes with perfluorocarboxylic and per-lluorosulfonic acid groups can be prepared by lamination of two different films containing the respective polymers " or by chemical conversion of perfluorosulfonic acid to perfluorocarboxylic acid. " The latter method is preferred to achieve the desired thickness of 5-10 fim of the carboxylic add pendant group. 

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... 

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