Tetrafluoroethylene thermal stability

Practicality has been an issue since many of the solvents referred to prior to 1994 have been quite expensive and the few others available have not had sufficient thermal stability to make them useful commercially. This chapter reviews our recent discovery of several commercially available cyclic perfluorocarbons as well as other halogenated fluids (and even carbon dioxide) as solvents for tetrafluoroethylene-containing polymers. We will describe solvation at atmospheric pressure, under autogenous conditions and under superautogenous... 

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. 

Thermal Stability of Electron-Irradiated Poly(tetrafluoroethylene)... 

Perfluoroalkoxy resin (PFA) Copolymer of tetrafluoroethylene (TFE) with perfluoro(propylvinyl ether), an engineering thermoplastic characterized by excellent thermal stability, release properties, low friction and toughness. Its performance is comparable to poiytetrafluoroethylene (PTFE) with the difference that it is melt processible. 

A new high-performance elastomer, prepared from tetrafluoroethylene (TFE) and perfluoro(methyl vinyl ether) (PMVE), and characterized by outstanding resistance to chemical attack and excellent thermal stability, was reported recently by Barney et al. (I) of our laboratory. That paper described a rubbery perfluorinated dipolymer that could not be crosslinked using ordinary techniques because of its chemical inertness, and also a terpolymer in which an unspecified third monomer was used to introduce active crosslinking sites. 

Fluorine substitution on carbon confers particular reactivity because of its particular properties Fluorine as the most electronegative element forms very strong CF bonds which are sized to "cover" perfluorocarbons tightly. Polytetrafluoroethylene (Teflon) is one practical example illustrating the exceptional chemical and thermal stability of saturated perfluorocarbons in a sharp contrast to explosive tetrafluoroethylene or to fluoroacetylenes. 

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. 

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. 

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. 

Teflon AF is an amorphous copolymer of tetrafluoroethylene (TFE) and 2,2-bis(trifluoromethyl)-4,5-difluoro-l,3-dioxole (PDD). It combines the properties of amorphous plastics, such as optical transparency and solubihty in organic solvents, with those of perfluorinated polymers, including high thermal stability, excellent chemical stability, and low surface energy. Moreover Teflon AF exhibits the lowest dielectric constant (1.90 for Teflon AF 2400) and the lowest re-... 

Kalrez Dupont s trade name for fluoroe-lastomers made from tetrafluoroethylene, perfluorovinylmethyl ether, and a small percentage of cross-linkable monomer. These elastomers combine the rubbery properties ofviton with the thermal stability, chemical resistance, and electrical characteristics of tetrafluoroethylene resin. Harper CA (ed) (2002) Handbook of plastics, elastomers and composites, 4th edn. McGraw-Hill, New York. Ash M, Ash I (1982-1983) Encyclopedia of plastics polymers, and resins, vols 1-3. Chemical Publishing Co., New York. 

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