Tetrafluoroethylene thermal oxidation

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. 

Fig. 51 Evolution of CL intensity assessed in argon (white) and oxygen (dark grey) during thermal oxidation of poly (tetrafluoroethylene) (Halon G-80) at 81 "C. The data were taken from [77M1].

Tetrafluoroethylene-ethylene copolymers (TFE-E) are used as insulation material for cables and wires used under extreme conditions. However, at high processing temperatures (280 to 340 °C), thermal-oxidative processes cause the separation of hydrofluoric acid and thus property deterioration [571],... 

Perfluoropropene oxide is a convenient, volatile, thermal source of difluoro-carbene, and its use in the preparation of fluorocyclopropanes has been further exemplified, perfluorinated, polyfluorinated, and hydrocarbon olefins being employed as substrates (see also p. 17) it has also been employed to convert perfluorobut-2-yne into 3,3-difluoro-l,2-bis(trifluoromethyl)cyclo-propene. Qose examination of the reaction between the epoxide and a mixture of cis- and rra .r-l-chloro-l,2-difluoroethylene at ca. 200°C has revealed that stereospecific addition of difluorocarbene takes place, but that loss of configuration can subsequently result from slow thermal isomerization of the cyclopropane product. Thermal decomposition of perfluoropropene oxide at 200 "C in the absence of a trap yields mainly perfiuorocyclo-propane and trifluoroacetyl fluoride together with tetrafluoroethylene, perfluoroisobutene oxide, perfluorobut-l-ene, and poly(difluoromethylene). 

Hydroxymethylmethyldiazirine (209 unprotonated) formed propionaldehyde as the sole product by thermal nitrogen extrusion 4-hydroxy-l,2-diazaspiro[2.5]oct-l-ene (218) formed a mixture of cyclohexanone (73%), cyclohexenol (21%) and cyclohexene oxide (5%). Thermal decomposition of difluorodiazirine (219) was investigated intensively. In this case there is no intramolecular stabilization possible. On heating for three hours to 165-180 °C hexafluorocyclopropane and tetrafluoroethylene were formed together with perfluorofor-maldazine 64JHC59). 

The thermal stability of polytetrafluoroethylene oxide and PTFE have been compared under the same conditions by Donato et al. [263] between 450 and 600°C. The decomposition rate has a maximum at 628°C for the oxide and at 568°C for PTFE. The activation energy for the first-order degradations are 98 kcal mole"1 between 8.5 and 85% for the oxide polymer and 85 kcal mole-1 between 523 and 571°C for PTFE. The rate of weight loss is less than 1.2% per min for both polymers below T = 550°C for the oxide and T = 590°C for PTFE. The oxide, however, loses weight below 390° C whereas PTFE does not. The main components of the volatile material are trifluoroacetyl fluoride, carbonyl fluoride and tetrafluoroethylene. An end-initiated thermal degradation with small zip length is proposed. 

TETRAFLUOROETHYLENE or 1,1,2,2-TETRAFLUOROETHYLENE (116-14-3) F2C=CF2 Highly reactive, thermally unstable, flammable gas (flash point <32°F/<0°C). Explodes underpressure. Able to form unstable peroxides in air. If inhibitor (usually limolene) is not present in adequate concentrations, explosive polymerization may occur above2025 mm Hg/2.66 bars at normal tenqjerature. Inhibited monomer will explode on contact with iodine pentafluoride and other substances, or in elevated temperatures. Violent reaction with chloro-peroxytrifluoromethane, difluoro-methylene dihypofluorite dioxygen difluoride, halogens, oxidizers, oxygen, sulfur trioxide, triboron pentafluoride. Incompatible with ethylene, hexafluoro-propene forms an explosive peroxide. Normal gases date containers when opened and discard after 12 months. 

Monosulfide polymer 19 is the most stable of the polymers discussed, not only in its resistance to base, oxidizing acids, and light but also in thermal stability. Degradation is slow at 300°C, but at 350°C chain scission results in an unzippering to evolve tetrafluoroethylene and di-thietane 6 (n = 2). The latter gives rise to polydisulfide 16 and may cycloadd to tetrafluoroethylene to form dithiane 7, the third major product. More likely under these conditions, however, is direct formation of 7 by a backbiting mechanism as illustrated below. 

Billow and Miller [187] also reported fairly similar results for poly(phenylene)s prepared from mixtures of terphenyls. Poly(m-phenylene) [188], phenyl-substituted polyphenylene [189] and perfluoropolyphenylene [190] have thermal and oxidative stabilities similar to that of poly(p-phenylene). Polyphenylenes synthesized by Wurtz-Fittig and Ullmann reactions were reported to withstand heating up to 500°-550°C [187,191,192]. Electrically conductive azo derivatives of polyphenylene (cTo= l-40ohm cm ) were stable up to 300°C without any noticeable decomposition, whereas the conductive block co-polymer of poly-phenylene with p-diethynylbenezene could withstand heating for many hours at 400°-450°C [I], Poly(p-phenylene) as well as poly(tetrafluoroethylene) have been reported to withstand a similar temperature without any thermal degradation and may be used safely up to similar... 

Fluoroelastomers with no C-H groups will be expected to exhibit a higher thermal stability. Du Pont thus developed a terpolymer of tetrafluoroethylene, perfluoro(methyl vinyl ether) and, in small amounts, a cure site monomer of undisclosed composition. This product, marketed as Kalrez, has excellent air-oxidation resistance up to 315°C and exhibits extremely low swelling in a wide range of solvents, which is unmatched by any other commercial fluroelastomer. Table 4.7 lists a number of commercial elastomers with their main properties and applications. 

Chemical in Japan where membrane cells are now dominant. Because of their Teflon -like chemical composition, perfluorinated membranes resist chemical and thermal degradation better than any of the hydrocarbon ion-exchange membranes that preceded them. For most of them the starting materials are perfluorinated monomers such as tetrafluoroethylene (TFE) CF2=CF2 and hexa-fluoropropylene oxide (FIFPO)... 

He et al. have prepared phosphonated aiyl trifluorovinyl ethers containing flexible oligo(ethylene oxide) units and subsequently homopolymerized these monomers by thermal cyclopolymerization in bulk at 180 °C. The resulting polymer was treated with bromotrimethylsilane to obtain the phosphonic acid derivative. The phosphonated trifluorovinyl ether monomers were also copolymerized with tetrafluoroethylene via free radical pol3Tnerization in an autoclave at 70 °C using l,l,2-trichloro-l,2,2-tri-fluoroethane as solvent. Moreover, radical terpolymerizations of the same trifluorovinyl ether monomers were performed with mixtures of... 

It is also possible to have halogen side groups, such as fluorine and chlorine. Polymers with fluorine in their side groups have extreme hydrophobicity and water insolubility. This raises the thermal and oxidative stability and confers solvent, fuel and oil resistance. Some examples of fluoro polymers are poly(tetrafluoroethylene) (Teflon),... 

A combination of gas chromatography and either electron-impact or chemical ionization mass spectrometry has been used to analyse the products of thermal degradation of poly(vinyl fluoride) and of a number of other polymers [poly(vinyl chloride), aromatic polyimides, polyurethane]. The degradation of poly(vinyl-idene fluoride) has been related to its crystalline form. It is claimed that dehydrofluorination may take place preferentially in crystalline segments containing trans sequences. Thermo-oxidative breakdown is modified if vinylidene fluoride is copolymerized with tetrafluoroethylene or hexafluoroacetone. Dehydrofluorination occurred in both copolymers, but in the latter it was preceded by cleavage of the H from the CHj group in the alpha position to the ether bond followed by scission of the C-0 bond. ... 

Apart from the fluoro monomers vinyl fluoride (VF), vinylidene fluoride (VF2), and tetrafluoroethylene (TFE), only chlorofluoroethylene has found commercial use as homopolymer. It is applied as thermoplastic resin based on its vapor-barrier properties, superior thermal stability (Tdec > 350 °C), and resistance to strong oxidizing agents [601]. Chlorofluoroethylene is homo- and copolymerized by free-radical-initiated polymerization in bulk [602], suspension, or aqueous emulsion using organic and water-soluble initiators [603,604] or ionizing radiation [605], and in solution [606]. For bulk polymerization, trichloroacetyl peroxide [607] and other fluorochloro peroxides [608,609] have been used as initiators. Redox initiator systems are described for the aqueous suspension polymerization [603,604]. The emulsion polymerization needs fluorocarbon and chlorofluorocarbon emulsifiers [610]. 

Copolymers of tetrafluoroethylene with perfluoro-alkylvinyl ethers were the ultimate elastomers for fluid, chemical, thermal and oxidative resistance. Cure chemistry mainly determined tensile properties, compression set resistance and upper use-temp. The chemistry was described for a perfluoroelastomer using a nitrile-substituted perfluoroalkylvinyl ether as cure-site monomer. It cured by trimerisation of the nitriles to triazine functionality and was devoid of any C-H bonds. Physical properties and thermal resistance in air over 300C were excellent. Peroxide-curable perfluoroelastomers, using hydrocarbon crosslinkers, were limited in performance. 3 refs. 

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