PSEPVE

The synthesis of the monomers as well as the polymerization of PFSA membranes involve dangerous reactions under conditions of high pressure and temperature. Additionally, the synthesis of the comonomer that is commonly referred to as perfluorosulfonylfluoride ethyl propyl vinyl ether (PSEPVE) involves numerous steps with low yields. These factors contribute to the cost of these materials. The synthesis routes described in detail by Doyle and Rajendran are summarized here. The synthesis of the long-chain PFSA monomers used in commercial systems like Nafion, Flemion, and Aciplex proceeds through... 

FIGURE 27.25 Synthesis process for Nation membrane comonomer PSEPVE. (Reproduced from Doyle, M. and Rajendran, G., in W. Vielstich, H.A. Gasteiger, and A. Lamm (Eds.), Handbook of Fuel Cells Fundamentals, Technology and Applications, Vol. 3, J. Wiley Sons, Chichester, 2003. With permission.)... 

Industrial production of perfluorinated ionomers, Nafion membranes, and all perfluorinated membranes is costly due to several factors first, the monomers used are expensive to manufacture, since the synthesis requires a large number of steps and the monomers are dangerous to handle. The precautions for safe handling are considerable and costly. Secondly, the PSEPVE monomer is not used for other applications, which limits the volume of production. The most significant cost driver is the scale of production. Today, the volume of the Nafion market for chlor-aUcali electrolysis (150,000 m year ) and fuel cells (150,000 m year ) is about 300,000 m year resulting in a production capacity of 65,000 kg year. When compared to large-scale production of polymers like Nylon (1.2 x 10 m year ), the perfluorinated ionomer membrane is a specialty polymer produced in small volumes. 

Takasaki et al. [47] assigned the chemical shifts of PSEPVE-containing copolymers based on smaller model compounds. The relatively high insolubility of PSEPVE-containing polymers inhibited their ability to produce concentrated samples for 2D-NMR studies. This resulted in spectra with few peaks. Perfluoro(2,5,8-trimethyl-3,6,9-trioxadodecanoyl)fluoride and perfluoro(2-ethoxyethane) sulfonic acid were chosen to represent two halves of PSEPVE. These compounds were then studied with 19f 13c HSQC, F-1 E COSY, and CIGAR-HMBC. 

Baiagern et al. [8] assigned hydrolyzed poly(TEE-co-PSEPVE) chemical shifts through characterization of the prepolymer, the sulfonyl fluoride form of Nafion perfluoropolymer membrane (12). It was assumed that the chemical shifts of the prepolymer would closely match those of the final polymer since the structures are nearly identical. The perfluorinated Nafion prepolymer was characterized with i F-i F selective COSY and gradient crisis -HSQC (gc2HSQC). 

Nafion is a random copolymer of tetrafluoroethylene (T EE) and perfluoro sulfonyl-fiuoride ethyl propyl vinyl ether (PSEPVE), made by free radical polymerization. The sulfonyl fluoride terminus in the polymer is converted to the sulfonate salt by basic hydrolysis, which produces either the Na or form of Nafion. Ioti exchange with sulfuric acid produces the sulfonic acid form shown in Fig. 1. The copolymer ratio (x) is defined by the equivalent weight, EW = lOOx + 444 g-polymer/mol-S03. Details of the monomer synthesis and subsequent conversimi processes are summarized by Doyle and Rajendran [4]. 

Sulfonyl fluoride vinyl ether (PSEPVE, DuPont)... 

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