Tetrafluoroethylene oxide

Perfluoroepoxid.es were first prepared ia the late 1950s by Du Pont Co. Subsequent work on these compounds has taken place throughout the world and is the subject of a number of reviews (1 5). The main use of these epoxides is as intermediates in the preparation of other fluorinated monomers. Although the polymerisation of the epoxides has been described (6—12), the resulting homopolymers and their derivatives are not significant commercial products. Almost all the work on perfluoroepoxides has been with three compounds tetrafluoroethylene oxide (TFEO), hexafluoropropylene oxide (HFPO), and perfluoroisobutylene oxide (PIBO). Most of this work has dealt with HFPO, the most versatile and by far the most valuable of this class of materials (4). 

Tetrafluoroethylene Oxide TFEO has only been prepared by a process employing oxygen or ozone because of its extreme reactivity with ionic reagents. This reactivity may best be illustrated by its low temperature reaction with the weak nucleophile, dimethyl ether, to give either of two products (47) (eq. 10). 

They were the first to synthesize (FCO—)2 and CF3OCFO. They also found that CO added to CF30 radicals. The radiolysis-induced oxidation has been emphasized by Mele, Lenzi, and their co-workers at the University of Rome, Italy. Apparently they were the first to isolate and characterize tetrafluoroethylene oxide. Gozzo and his co-workers at Milan, Italy, examined the photochemical and low-temperature thermal oxidation of C2F4. 

Synthetic methods have limited the preparation of saturated perfluoropolyethers. The most successful perfluoropolyether synthetic chemistry has been DuPont s anionic polymerization of perfluoroepoxides, particularly hexafluoro-propylene oxide and tetrafluoroethylene oxide (39). Their synthetic procedure is a three-step scheme for saturated perfluoropolyether production involving oxidation of perfluoroolefins to perfluoroepoxides, anionic polymerization to acyl fluoride terminated perfluoropolyethers, and conversion of acyl fluoride end groups to unreactive end groups by decarboxylation reactions or chaincoupling photolytic decarboxylate reactions. 

When heated above 170"C hexafluoropropylene oxide (5) is a source of difluorocarbene thus, heating 5 in the presence of an alkene allows the synthesis of fluorinated cyclopropanes under neutral conditions.14 16 The less readily available tetrafluoroethylene oxide (6) is also a precursor of difluorocarbene.17... 

At 100 °C, tetraflUoroethylene reacts slowly with oxygen [147]. Thus, in an equimolar mixture after 14 h, about 90 % of the oxygen and 85 % of the tetraflUoroethylene have disappeared, the main products being approximately equal amounts of carbonyl fluoride and hexafluorocyclopropane together with a little tetraflUoroethylene oxide. 

Tetrafluoroethylene oxide decomposes through the biradical to give perfluoro-formaldehyde and difluorocarbene . The latter intermediate could be trapped as perfluorocyclopropane by tetrafluoroethylene. The mechanism proposed is... 

The anionic oligomerisation of hexafluoropropylene oxide or tetrafluoroethylene oxide is an alternative source of the hydrophobic/oleophobic fluorocarbon fragment synthesis [126, 128] ... 

Although large number of fluorinated epoxides has been synthesized, to date, HEPO is the only compound that has commercial interest. Tetrafluoroethylene oxide, TEEO, has been prepared and is extremely reactive, isomerizing easily to... 

Tetrafluoroethylene oxide features, with perfluoropropene oxide, in recent Russian work on fluoride-initiated reactions of perfluorodicarboxylic acid fluorides (perfluoromalonyl and perfluoroadipoyl difluoride) with peifluoro-oxirans,... 

For aerospace applications, several advanced sealants have been mentioned cyanosilicones (123),fluoroalkyl-arylenesiloxanylene (FASIL) (124), phosphonitrilic fluo-roelastomers (PNF ) (125,126), flexible polyimide (127), tetrafluoroethylene oxide phenylquinoxaline elastomer (FEX) (128), perfluoroalkyl ethers (129), etc. These advanced sealants have been used for fuel tank sealing, channel sealing, filleting, aerodynamic smoothing, and other assemblies. Basically, they should be high-temperature serviceable, fault-tolerant, and adhere well to metals and/or composites. 

Tetrafluoroethylene oxide can be polymerized only at temperatures around -196 C, since the monomer is destroyed by side reactions at higher temperatures. 

Before we discuss our efforts to prepare long-chain fluoroethers that have difunctional termination, let us briefly consider some of the fluoroether work in the literature. Although much work has been done with tetrafluoroethylene oxide, it is quite unstable and therefore difficult to handle experimentally. Consequently, efforts have been centered on hexafluoropropylene oxide polymerization. 

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