Tetrafluoroethylene thermal decomposition

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). 

Thermal decomposition is a major route to smaller perfluonnated molecules Tetrafluoroethylene pyrolyzed at 1100-1300 °C with carbon dioxide gives a mixture of tetrafluoromethane (19 9%), hexafluoroethane (61 3%), and carbonyl fluoride (18 6%) [87]... 

Difluorocarbene can be generated by high-temperature reaction of chlorodifluoromethane in the production of tetrafluoroethylene (TFE) (equation 48). Another method of in situ generation of the carbene is thermal decomposition of... 

Chemically, difluorodiazirine appears to be remarkably inert. Like diazirine itself, however, it is explosive. It undergoes thermal decomposition above about 160°C. Photolysis of this compound at room temperature produces only tetrafluoroethylene and nitrogen, presumably by the reactions... 

Atkinson et a/. - - have reported that the thermal decomposition of tetra-fluoroethylene can be divided into three temperature phases (see also ref. 454). At temperatures below 550 °C perfluorocyclobutane is the main product above 550 °C the equilibrium mixture of tetrafluoroethylene and perfluorocyclobutane decomposes to form perfluoropropene by a first-order reaction, and perfluoro-propene decomposes in turn by a 1.5-order process to perfluoroisobutene above 700 °C the perfluoroisobutene decomposes by a first-order reaction to perfluoro-ethane and non-volatiles. The observations are shown to be consistent with a reaction scheme involving CFj radicals in Phases 1 and 2, and CFj radicals in Phase 3, as follows... 

Thermal decomposition products of PTFE (up to 500 C) are mainly the monomer, tetrafluoroethylene and some perfluoro compounds (such as, perfluoroisobutylene). Between 500 °C to 800 °C, the decomposition product is mainly carbonyl fluoride, which can hydrolyse easily (to produce toxic and corrosive hydrofluoric acid and carbon dioxide). 

The thermal decompositions of perfluorocyclobutane diluted with water vapour to give tetrafluoroethylene (91.4% yield based on 86% conversion of cyclo-C4F8 at 850 °C) and of perfluorocyclopropane and perfluoro(methylcyclopropane) to yield difluorocarbene have been mentioned in the patent literature and in papers ... 

Thermal decomposition of a y-irradiated poly( vinyl fluoride) occurred in two main steps firstly, elimination of hydrogen fluoride and secondly, main chain scission to yield unsaturated hydrocarbons." Polytetrafluoroethylene and the copolymer of tetrafluoroethylene and hexafluoropropene were degraded in various atmospheres and the decomposition products analysed." - For an inert atmosphere over twenty different fluorinated products were identified. For air the major products were COF, CF , and COj with minor amounts of fluorocarbons. The gaseous and solid decomposition products have also been analysed from the thermal degradation of poly(carbon monofluorides) containing different proportions of fluorine. Kinetic data were also obtained. 

The temperatures quoted are those at which decomposition becomes appreciably rapid. Presumably metal fluorides are also formed in these decompositions but this has not been proven. A reaction which is apparently the reverse of these pyrolyses was mentioned above, namely the addition of platinum-fluorine bonds to tetrafluoroethylene 118). The thermal decomposition of perfluoroalkyl and polyfluoroalkyl derivatives of main group elements such as boron, silicon, or tin was mentioned in earlier sections of this chapter. Transfer of fluorine atoms from the side chains on heating was also a characteristic property. However, it is interesting to compare the reaction (97),... 

Tetrafluoroethylene is obtained by the thermal decomposition of this monochlorodifluoro-methane (known as Freon) in a continuous noncatalytic gas-phase reaction, carried out at or below atmospheric pressure at temperatures from 600°C to 900°C ... 

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). 

Thermal decomposition of the p-sultone CFa CFg SOj-O, prepared from tetrafluoroethylene and sulphur trioxide, has been mentioned in the patent literature as a source of trifluoroacetyl fluoride and its decomposition in the presence of sulphuric acid has been claimed to yield difluoroketene (see p.40). 

The fragmentation reaction sequence is analogous to the thermal decomposition mechanism of poly(tetrafluoroethylene). 

TG-IR has also been used to examine the thermally induced decomposition products of polyvinyl chloride (PVC), polyacrylamide, tetrafluoroethylene-propylene, styrene-... 

Thermal degradation does not occur until the temperature is so high that primary chemical bonds are separated. It begins typically at temperatures around 150-200 °C and the rate of degradation increases as the temperature increases. Pioneering work in this field was done by Madorsky and Straus (1954-1961), who found that some polymers (poly (methyl methacrylate), poly(oc-methylstyrene) and poly (tetrafluoroethylene)) mainly form back their monomers upon heating, while others (like polyethylene) yield a great many decomposition products. 

One of the best-known thermal reactions of fluorine compounds is the pyrolysis of chlorodifluoromethane to tetrafluoroethylene as used in the production of Teflon polymer. This reaction was described by Park et in 1947, and Nor-ton" in 1957 reported an activation energy of 49 kcal.mole for the decomposition over silica at 425-525 °C. More recently, Gozzo and Patrick have made a kinetic study of the process using a helium flow system at 670-750 °C with a surface conditioned platinum tubular reactor. HCl is found to retard the raction and the following mechanism has been proposed... 

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. 

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... 

Trifluoronitrosomethane-tetrafluoroethylene copolymer has good thermal stability. The copolymer does not bum but decomposition into gaseous products begins at about 200°C. The glass transition temperature of the copolymer is -54 C and vulcanizates remain serviceable down to about -40°C. A limitation of the vulcanizates is their low tensile strength, although silica effects some reinforcement. 

There are a number of ways to prepare HFP. Excellent hexafluoropropylene yields from the thermal degradation of heptafluorobutyrate (CF3CF2CF2COONa) have been reported.Cracking of tetrafluoroethylene in a stainless steel tube at 700-800°C under vacuum is an efficient route for the production of HFP. TFE conversions up to 72% and HFP yields of 82% have been reportedf lP Octa-fluorocyclobutane (TFE dimer), octafluoroisobutylene, and some polymer are the major side products of cracking. The presence of a small amount (3-10%) of chlorodifluoromethane stops the formation of poly-mer.P lThermal decomposition of PTFE under 20 ton-vacuum at 860°C yields 58% hexafluoropropylene. 1... 

Infrared spectroscopy and thermogravimetry have been used in polymer analysis for many years. By coupling the effluent of thermogravimetry to an infrared gas cell, TG/IR (sometimes known as evolved gas analysis) has been used to examine the thermally induced decomposition products a variety of polymers including of poly(vinyl chloride) (7), polyacrylamide (2), tetrafluoroethylene-propylene (3) and ethylene-vinyl acetate (4) copolymers, as well as styrene-butadiene composite (5). 

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