F Tetrafluoroethylene

Propynol, Mercury(II) sulfate, Sulfuric acid, Water, 4479 Styrene, Air, Polymerising styrene, 2945 Styrene, Butyllithium, 2945 Styrene, Dibenzoyl peroxide, 2945 Styrene, Initiators, 2945 f Tetrafluoroethylene, 0628... 

D. Fluorocarbon Polymers. Four different fluorocarbons account for the bulk of the laboratory applications polytetrafluoroethylene, Teflon PTFE po-ly(chlorotrifluoroethylene), KEL-F tetrafluoroethylene-hexafluoropropylene copolymer, Teflon FEP and tetrafluoroethylene-perfluorovinyl ether copolymer, PFA. These polymers are inert with most chemicals and solvents at room temperature and exceptionally inert with oxidizing agents. They also have an exceptional resistance to temperature extremes. However, they are decomposed by liquid alkali metals, solutions of these metals in liquid ammonia, and carban-ion reagents such as butyllithium. Teflon retains some of its compliance at liquid hydrogen temperature. The maximum temperature which is recommended for continuous service is 260°C for Teflon PTFE and PFA, and about 200°C for Kel-F and Teflon FEP. 

The irradiation of poly(vinyhdene fluoride) (PVDF) brings about Httle enhancement in the crystallinity for irradiation doses of about 100 kGy similar to poly(ethylene-a/f-tetrafluoroethylene) (ETFE). However, beyond 100 kGy, ETFE shows significant loss in the crystallinity but PVDF remains almost unchanged [34]. 

Although the CFCs and HCFCs are not as stable as the PFCs, they still can be rather stable compounds (3,11)- Dichlorodifluoromethane, CCI2F2, is stable at 500°C in quartz CCl F and CHCIF2 begin to decompose at 450 and 290°C, respectively (7). The pyrolysis of CHCIF2 at 650—700°C in metal tubes is the basis of a commercial synthesis of tetrafluoroethylene ... 

Photooxidation of tetrafluoroethylene (TFE) and hexafluoropropylene (HEP) yield peroxides that can be decomposed to esters and ultimately long-chain ether-containing carboxyUc acids. Equation 6 shows a simplified version of what occurs during photooxidation and workup (TFE R = F,... 

Fluorocarbon—long-chain synthetic polymer composed of tetrafluoroethylene units. 1.0-2.0 F E E E G 2.30 5501... 

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

The behavior of strained,/Zuorimiret/ methylenecyelopropanes depends upon the position and level of fluorination [34], l-(Difluoromethylene)cyclopropane is much like tetrafluoroethylene in its preference for [2+2] cycloaddition (equation 37), but Its 2,2-difluoro isomer favors [4+2] cycloadditions (equation 38). Perfluoromethylenecyclopropane is an exceptionally reactive dienophile but does not undergo [2+2] cycloadditions, possibly because of stenc reasons [34, 45] Cycloadditions involving most possible combinations of simple fluoroalkenes and alkenes or alkynes have been tried [85], but kinetic activation enthalpies (A/f j for only the dimerizations of tetrafluoroethylene (22 6-23 5 kcal/mol), chlorotri-fluoroethylene (23 6 kcal/mol), and perfluoropropene (31.6 kcal/mol) and the cycloaddition between chlorotnfluoroethylene and perfluoropropene (25.5 kcal/mol) have been determined accurately [97, 98] Some cycloadditions involving more functionalized alkenes are listed in Table 5 [99. 100, 101, 102, 103]... 

Materials compatibility. We use scrupulously clean and scratch-free FEP (FEP is the acronym for the copolymer of tetrafluoroethylene and hexafluoropropylene) tubing for handling our mixtures of fluorine and nitrogen at ambient temperature. Corrugated FEP tubing is convenient for making strain-free assemblies. We have found that Monel is excellent for use with dry molten KF-2HF. Mild steel corrodes slowly and stainless steels corrode rapidly. Kel-F polychlorotrifluoroethylene is satisfactory for use with HF and with KF-2HF polypropylene and polymethylpentene are not satisfactory. 

R.J. Lehnert, P.J. Hendra, N. Everall and N.J. Clayden, Comparative quantitative study on the crystallinity of poly(tetrafluoroethylene) including Raman, infra-red and F nuclear magnetic resonance spectroscopy, Polymer, 38(7) (1997) 1521-1535. 

The first [2 -t- 2] cycloaddition of methylenecyclopropane which has been reported involves the use of tetrafluoroethylene (482) (Table 38, entry 1) [131], an olefin having a high tendency to give cycloadditions in a [2 -f 2] fashion, which are considered to occur in a two-step process involving diradical intermediates. In the same article, the author reports unsuccessful attempts to react methylenecyclopropane with maleic anhydride or acrylonitrile [131]. 

Examples of radiation-grafted PEMs poly(ethylene-flZf-tetrafluoroethylene)-gra/f-poly(sty-rene sulfonic acid) (ETFE-g-PSSA), 30 PVDF-g-PSSA, 31 and poly(tetrafluoroethylene-co-hexafluoropropylene)-g-PSSA (FEP-g-PSSA), 32. 

The processability of fluorine-containing polymers is improved by replacement of one or more of the fluorine atoms. Replacing one of the eight fluorine atoms with a trifluoromethyl group gives a product called FEP or Viton, actually a copolymer of tetrafluoroethylene and hexafluoropropylene (Equation 6.53). Polytrifluoromonochloroethylene (PCTFE, Kel F) (Equation 6.54), in which one fluorine atom has been replaced by a chlorine atom, has a less regular structure and is thus more easily processed. Poly(vinylidene fluoride) (PVDF, Kynar) (Equation 6.55) is also more easily processable but less resistant to solvents and corrosives. 

Firstly from a comparison of the integrated area ratios for the F ls and Cls levels and secondly from the individual components of the Cis levels. This readily establishes that the materials are copolymers of ethylene and tetrafluoroethylene which are largely alternating in character and that the outermost surface sampled by ESCA is identical in composition to the bulk. This is shown in Table 4 where a comparison is drawn with compositions determined by standard microanalysis (carbon by combustion, fluorine by potassium fusion). ESCA is highly competitive as a routine means of establishing compositions for fluoropolymers in particular, in terms of accuracy, nondestructive nature and speed. 

Fig. 35. Plot of intensity ratios of components of CXi levels and of the total F ls to Cls levels as a function of take off angle for untreated and Argon glow discharge treated samples of an ethylene-tetrafluoroethylene copolymer...

Synthetic methods involving halogenation with ring formation have been mentioned earlier (Section II, B), as has the preparation of octa-fluorooctahydrodithieno[2,3-6 2, 3 -[Pg.195]

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