Perfluoro vinyl ethers

The typical membranes are homogeneous, and are preferably reinforced with an inert material. The chemical composition of the membranes are hydrolyzed copolymers of tetrafluoroethylene (TFE) and perfluoro vinyl ether monomer containing an ion-exchange group or its precursor (PVEX), represented by the following general formula (1 - 21). 

El-S.A. Hegazy, A.M. Dessouuki, A.M. Rabie and I. Ishigaki, Membranes obtained by preirradiation grafting of acrylic acid onto poly(tetrafluoroethylene-perfluoro-vinyl ether), J. Polym. Sci., Polym. Chem. Ed. 1984, 22, 3673-3685. 

FLUORINECOMPOUNDS, ORGANIC - FLUOROETHERS AND FLUORO AMINES] (Volll) Perfluoro (methyl vinyl ether) [1187-93-5]... 

FLUORINECOPPPOUNDS,ORGANIC - FLUORINAPED ALIPPiATIC COPPPOUNDS] (Vol 11) Poly(tetrafluoroethylene-co-perfluoro(methyl vinyl ether)... 

In the 1960s and 1970s, additional elastomers were developed by Du Pont under the Viton and Kalrez trademarks for improved low temperature and chemical resistance properties using perfluoro(methyl vinyl ether), CF2=CFOCF3, as a comonomer with vinyUdene fluoride and/or tetrafluoroethylene (12,13) (see Fluorine compounds, organic-tethafluoroethylene polypous and copolyp rs). 

Fig. 3. The percent volume swell in benzene after seven days at 21°C compared with the wt % of fluorine on standard recommended compounds. A, copolymers of vinyUdene fluoride—hexafluoropropylene B, terpolymers of vinyUdene fluoride—hexafluoropropylene—tetrafluoroethylene C, terpolymers of vinyhdene fluoride—hexafluoropropylene—tetrafluoroethylene-cure site monomer D, copolymer of tetrafluoroethylene—perfluoro(methyl vinyl ether)-cure...

Somewhat between PTFE and PFA materials is the product Hostaflon TFM, which is a copolymer of TFE and a small amount of the perfluoro(propyl vinyl ether). It has improved impact strength and weldability and has been promoted as a suitable material for forming into bottles. Yet another TFE-perfluoroalkoxy copolymer was introduced by Du Pont in 1979 as Teflon EPE. This material had a somewhat lower melting point (295 °C) than the more common PFA fluoropolymers but it is no longer marketed. 

Tetrafluoroethylene-peifluoro(methyl vinyl Kalrez Du Pont -40% perfluoro(methyl vinyl ether) Ex. air oxidation... 

In attempts to further improve the stability of fluorine-containing elastomers Du Pont developed a polymer with no C—H groups. This material is a terpolymer of tetrafluoroethylene, perfluoro(methyl vinyl ether) and, in small amounts, a cure site monomer of undisclosed composition. Marketed as Kalrez in 1975 the polymer withstands air oxidation up to 290-315°C and has an extremely low volume swell in a wide range of solvents, properties unmatched by any other commercial fluoroelastomer. This rubber is, however, very expensive, about 20 times the cost of the FKM rubbers and quoted at 1500/kg in 1990, and production is only of the order of 1 t.p.a. In 1992 Du Pont offered a material costing about 75% as much as Kalrez and marketed as Zalak. Structurally, it differs mainly from Kalrez in the choice of cure-site monomer. 

Rase-catalyzed reaction of alcohol favors addition, whereas increasing amounts of alkoxide favor addition-elimination reactions. Perfluoro-2-methyl-2-pentene and methanol form the saturated ether, whereas two equivalents of sodium methoxide form the vinylic ether [S] (equation 4). 

Miller et al. [9] hypothesized rules on the regioselectivity of addition from the study of the base-catalyzed addition of alcohols to chlorotnfluoroethylene. Attack occurs at the vinylic carbon with most fluorines. Thus, isomers of dichloro-hexafl uorobutene react with methanol and phenol to give the corresponding saturated and vinylic ethers The nucleophiles exclusively attack position 3 of 1,1-dichloro-l,2,3,4,4,4-hexafluoro-2-butene and position I of 4,4-dichloro-l,l,2,3,3,4-hexafluoro-1-butene [10]. In I, l-dichloro-2,3,3,4,4,4-hexafluoro-l-butene, attack on position 2 is favored [J/] (equation 5) Terminal fluoroolefms are almost invariably attacked at tbe difluoromethylene group, as illustrated by the reaction of sodium methoxide with perfluoro-1-heptene in methanol [/2J (equation 6). 

Tetrafluoroethylene-Perfluoro(propyl vinyl ether) Copolymers (PFA)... 

Copolymerizahon of TFE and perfluoro(propyl vinyl ether) (PPVE) yields melt-processable, linear polymers known as perfluoroalkoxy (PFA) resins of the following general structure... 

During polymerization, a polymeric radical with a perfluoro(alkyl vinyl ether)-derived active center can have one of two fates it can cross-propagate to tetrafluoroethylene or it can undergo P-scission to yield an acid-fluoride-terminated polymer chain and generate a peduoroalkyl radical capable of initiating further polymerization (ie., chain transfer to monomer). These scenarios are illustrated in Scheme 3. 

Many other crosslinking reactions are used in commercial applications. A variety of halogen-containing elastomers are crosslinked by heating with a basic oxide (e.g., MgO or ZnO) and a primary diamine [Labana, 1986 Schmiegel, 1979]. This includes poly(epichlorohydrin) (Sec. 7-2b-6) various co- and terpolymers of fluorinated monomers such as vinylidene fluoride, hexafluoropropene, perfluoro(methyl vinyl ether), and tetrafluoroethylene (Sec. 6-8e) and terpolymers of alkyl acrylate, acrylonitrile, and 2-chloroethyl vinyl ether (Sec. 6-8e). 

Perfluoro(methyI vinyl ether) (1) gives perfluoro(ethyl methyl ether) (2) only at 40 C. The reaction rate and the yield of the end product are rather low. 

Krespan also found that allyl alcohol added to 1-mcthoxy-2-(trifluoromethyl)tetrafluoro-propcnc, derived from perfluoro(2-mclhylpropene). to give the rearranged ester 5. a presage of the Johnson Claiscn rearrangement. Reactions of allylic alcohols with vinyl ethers derived from perfluoro(2-methylpropene) were subsequently studied by Andreev and co-workers11 and are discussed below. 

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