Perfluorocarbon polymers

Hydrocarbon Polymers. It is difficult to produce perfluorocarbon polymers by the usual methods. Many monomers, such as hexafluoropropylene, polymerize only slowly because of the steric hindrance of fluorine. Furthermore, some monomers are not very stable and are difficult to synthesize. Direct fluorination can be used for the direct synthesis of fluorocarbon polymers (68—70) and for producing fluorocarbon coatings on the surfaces of hydrocarbon polymers (8,29,44—47,49,68—71). 

The sorption behavior of perfluorocarbon polymers is typical for nonpolar partially crystalline polymers (89). The weight gain strongly depends on the solubihty parameter. Litde sorption of substances such as hydrocarbons and polar compounds occurs. 

It should not be thought, however, that perfluorocarbons are completely inert toward combustion. Even the very inert perfluorocarbon polymer polytetrafluoroethylene [PTFE, Du Pont s Teflon F(CF2CF2)nF] is thermodynamically unstable in oxygen with respect to CO2 and CF4 (Exercise 12.6) and can burn in a 95% 02/5% N2 mixture at 0.1 MPa, although combustion is hard to initiate because of the nonvolatility of PTFE and the resistance of the thermal degradation products to oxidation. Conflagrations involving more reactive, volatile fluorocarbons such as perfluoro-toluene have been reported.15... 

One of the technically and commercially most important cation-exchange membranes developed in recent years is based on perfluorocarbon polymers. Membranes of this type have extreme chemical and thermal stability and they are the key component in the chlorine-alkaline electrolysis as well as in most of today s fuel cells. They are prepared by copolymerization of tetrafluoroethylene with perfluorovinylether having a carboxylic or sulfonic acid group at the end of a side chain. There are several variations of a general basic structure commercially available today [11]. The various preparation techniques are described in detail in the patent literature. 

Elemental sodium, as well as other alkali metals, reacts with perfluorocarbon polymers by removing fluorine from them. This reaction has a practical application for improving surface wettability and adhesive bonding of perfluorocarbon polymers to other substrates.57... 

Since the direct synthesis of alkylchlorosilanes has enabled the industrial development of silicones, a-fluoroalkyl derivatives were also given some attention because perfluorosilicones presumably could combine the outstanding properties of both conventional silicones and perfluorocarbon polymers [1]. 

In the case of perfluorocarbon polymers, y is of the order of 19dyne/cm and y 0 because the surface configuration is not influenced by the contacting medium (air or vacuum). The value of y for water is of the order of 70dyne/cm. 

Ionomer membranes based on perfluorocarbon polymers became available In the late 196O s. These materials have excellent chemical resistance, thermal stability, mechanical strength and strong acid strength, A number of functionalities have been studied. Including carboxylate, sulfonate and sulfonamide, but only the first two are available as commercial materials. Ferfluorlnated lonomers have been evaluated as membranes In a variety of applications, such as water electrolysis, fuel cells, air driers, Donnan dialysis In waste metal recovery, and acid catalysts, but the primary interest in these materials is for the permselective membrane In electrochemical processes such as In the production of chlorine and caustic (58). 

Radical ions which have been studied include the phenylalkene cation in perfluorocarbon polymer films at 77 and both the 9-... 

T. Kuwata and S. Yoshikawa, Preparation method of cation exchange membranes. Jpn. Pat. JP 40-531 (examined application), 1965 M. Kato, K. Akiyama and M. Yamabe, New perfluorocarbon polymers with phosphoric groups, Rep. Res. Lab. Asahi Glass Co Ltd., 1983, 33, 135-142. 

There exist numerous references in the literature for the preparation of ion-exchange membranes by polymerization [19, 20, 21]. In recent years, membranes based on perfluorocarbon-polymers have proved to be very useful in the chlor-alkaline industry [22]. They were introduced first by DuPont as Nafion [23] and are prepared according to the following reaction scheme in a several-step procedure ... 

Phosphonated polymers have been proposed for fuel cells with the expectation of being thermally more stable and better retaining water than sulfonic groups [210, 211]. Phosphonated poly(phenylene oxide) [212], poly(4-phenoxy-benzoyl-l,4-phenylene) [213] and polysulfones [214, 215] have been reported. Phosphonated fluoromonomers were polymerized [164]. Characterization of phosphonated films in terms of their proton conductivity has been reported for some of the phosphonated polymers polyphosphazene [216], trifluoropolysty-rene [217], poly(4-phenoxybenzoyl-l,4-phenylene) [218]. Relatively low conductivity values were reported for most of the polymers prepared up to now. The values for polyphosphazene [216] and for perfluorocarbon polymers [219] were quite encouraging. Phosphonated poly(phenylene oxide) [211] was evaluated in fuel cell-tests. 

Z.M. Qiu, D.J. Burton, Preparation of perfluorocarbon polymers containing phosphonic acid groups. Journal of Fluorine Chemistry 82 (1997) 13-19. 

Scheme 13.3 Phosphonated fluorinated pol miers (a) poly(2,3,5,6-tetrafluoro-4-vinylphenylphosphonic acid), (b) phosphonated perfluorocarbon polymer,(c) phosphonated fluorinated copol)Tner, (d) phosphonated fluorinated poly(aiyl ether). ...

Thus I as the result of the lucky accident associated with the work on HFPO, the ultimate in thermoplastic perfluorocarbon polymers was commercialized in 1972, over ten years later. The long time between initial discovery and commercialization was only in part due to the enormous amount of new technology that had to be developed. Of equal importance was the lack of a clear cut market for this exotic polymer. 

Table 2.4. Sorption of Various Compounds by Perfluorocarbon Polymers at Room Temperature i...

A micro-planar electrode with long-term stability was developed by Matsumoto et al. [75], who used a perfluorocarbon polymer membrane. The electrode was not influenced by interferences (with exception of K2S with concentration exceeding 0.001 mol dm ). Yalcinkaya and Powner [76] have introduced a new type of miniaturized coated silver stripe reference electrode without internal solution for single use. 

Recent work has shown that Haloport F (a perfluorocarbon polymer) offers some advantages over polyethylene glycol 600 and Florex columns in the separation of vitamin A from vitamin D. 

Both perfluorosulfonate membranes and perfluorocarboxylate membranes are cation exchange membrane (cation Na ) and are based on perfluorocarbon polymer. However, the fixed group of perfluorosulfonate membranes is sulfonate pendant (-SO3-) while perfluorocarboxylate is carboxylate pendant (-COO-). This structure difference leads to different physicochemical properties. 

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