Sulfonyl-vinyl fluoride

Pazenok et al. [142] have reported that the reaction of a-fluoroethyl BT-sulfone 323 (Scheme 108) with aldehydes or ketones 324 affords vinyl fluorides 325. Sulfonyl anions were generated either with NaHMDS or with t-BuOK in THE In general, high chemical yields could be attained but the selectivity was poor. Representative applications of this reaction are shown in Table 29. 

These compounds are synthesized by the copolymerization of tetrafluoroethylene and alkyl vinyl ether with sulfonyl acid fluoride. Preparation of sulfonyl acid fluoride takes place by pyrolysis of the respective oxide to give the olenfinated structure [7], The thermoplastic produced is extruded into a film. The sulfonyl fluoride (-S02F) group present in the thermoplastic is converted to sulfonate (-S()3 Na+) with NaOH. This is called the neutral form of Nafion, and it is converted to the acid for and cast into a thin film by heating in alcohol at 250°C. At around 650/m2, the Nafion membranes are rather expensive when compared to hydrocarbon membranes, which are also used. 

The vinyl ether in the latter part of the equation is copolymetized with tetrafluoroethylene, and then the sulfonyl fluoride group is hydrolyzed under basic conditions in order to produce the ion-exchange membrane (44—46). 

Since PTFE was first synthesized more than 50 years ago, fluoropolymers have been produced by radical polymerization and copolymerizaton processes, but without any functional groups, for several reasons. First, the synthesis of functional vinyl compounds suitable for radical polymerization is much more complicated and expensive in comparison with common fluoroolefins. In radical polymerization of one of the simplest possible candidates—perfluorovinyl sulfonic acid (or sulfonyl fluoride—there was not enough reactivity to provide high-molecular-weight polymers or even perfluorinated copolymers with considerable functional comonomer content. Several methods for the synthesis of the other simplest monomer—trifluoroacrylic acid or its esters—were reported,1 but convenient improved synthesis of these compounds as well as radical copolymerization with TFE induced by y-irradiation were not described until 1980.2... 

Carbon dioxide has also proven to be an exemplary medium for the polymerization of TFE with perfluorinated alkylvinyl ether monomers containing sulfonyl fluoride such as CF2=CF0CF2CF(CF3)0CF2CF2S02F (PSEVPE). As seen in Table 13.2, the dramatic difference in the number of acid end groups between the commercial sample and those made in C02 indicates that chain-transfer processes stemming from vinyl ether radical arrangement are not nearly as prevalent in C02 as in conventional systems. 

These are good dienophiles. and aryl vinyl sulfones have found use as equivalents of ethylene and ketene through functional modifications of their adducts. However, as the base-induced elimination of a sulfinic acid to yield an olefin occurs only with difficulty, they are not direct precursors of acetylene equivalents, unless suitably modified as in ( )-l-phenyl-sulfonyl-2-trimethylsilyl ethylene (PhS02-CH=CH-TMS). In its cycloadducts the elimination to an alkene is smoothly realized by the fluoride ion. If an alkylation step is previously carried out on the adduct, the overall process realizes an indirect addition of a terminal acetylene, as in the examples given here [533]. 

For PEMFCs, the solid electrolytes are polymer membranes polymers modified to include ions, usually sulfonic groups. One of the most widely used membranes today is the polymer Nafion , created by the DuPont company. These membranes have aliphatic perfluorinated backbones with ether-linked side chains ending in sulfonate cation exchange groups [6, 7], Nafion is a copolymer of tetrafluoroethylene and sulfonyl fluoride vinyl ether [8] and has a semi-crystalline structure [9], This structure (which resembles Teflon ) gives Nafion long-term stability in oxidative or reductive conditions. The sulfonic groups of the polymers facilitate the transport of protons. The polymers consist of hydrophilic and hydrophobic domains that allow the transport of protons from the anode to the cathode [10, 11],... 

Lithiation of compound 560 with s-BuLi-TMEDA in THF at —78 °C following an inverse addition protocol provided the anion 561. It reacts with primary alkyl iodides and triflates, silyl chlorides, diphenyl disulfide, epoxides, aldehydes, ketones, imines, acyl chlorides, isocyanates and sulfonyl fluorides to yield the expected compounds 562 (Scheme 152). The transmetallation of compound 561 with ZnBr2 allowed the palladium-catalyzed cross-coupling reaction with aryl and vinyl bromides837. When the reaction was quenched with 1,2-dibromotetrafluoroethane, the corresponding bromide 562 (X = Br) is obtained838. 

A similar behavior has also been observed in membranes obtained by copolymerization. Many recent perfluorinated sulfonated membranes have been obtained by copolymerization of tetrafluoroethylene with a sulfonyl fluoride vinyl ether. This high molecular weight polymer has the following formula ... 

By heating with sodium carbonate the sulfonyl fluoride vinyl ether is formed which is then copolymerized with TFE. 

These adducts are heated with Na2C03 to form a sulfonyl fluoride vinyl ether, which is subsequently copolymerized with tetrafluoroethylene to form XR resin as ... 

A modification of the polymer that has been adopted by various groups is to have shorter side chains as compared to Nafion. Short side chains increase the crystallinity of the PFSA, thus reducing the solubility. Solvay Solexis has developed Aquivion, a membrane based on Hyflon, which is a copolymer of Teflon and sulfonyl fluoride vinyl ether with low EW (790-870) and good crystallinity, with proton conductivity values in the order of 30 mS cm at 120°C, 30% RH [22]. A similar approach is followed by 3M, who have shown 580 EW membranes approaching 100 mS cm at 120°C and RH 50% [23]. Gore recently reported values >50 mS cm at 30% RH and > 100 mS cm 50% RH with a new, undisclosed ionomers [24]. DuPont recently presented results on MEAs with new ionomer that showed a much reduced dependence on the RH as compared to Nafion-based membranes [17]. 

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