Teflon amorphous

Teflon AF Teflon amorphous fluoropolymer - Dupont trademark... 

Fig. 2.15 Isosteric heat of adsorption of nitrogen on molecular (low-evergy) solids and on carbons (high-energy solids), plotted as a function of i/n . (A) Diamond (B) gruphitized carbon black. P.33 (D) Benzene (E) Teflon. The curve for amorphous carbon was very close to Curve (A). (Redrawn from a Figure of Adamson . )...

In 1989 Du Pont introduced Teflon AF, said to be a copolymer of tetrafluoroethylene and trifluoromethyldifluorodioxol. This amorphous fluoro-polymer has a similar heat and chemical resistance to PTFE but possesses several notable properties, including ... 

Table 13.3 Typical properties of Teflon AF amorphous fluoropolymers...

A major development in fluoroplastks is the recent small scale production of Teflon AF, a noncrystaUme (amorphous) fluorocarbon polymer with a high glass transition temperature (240 °C) This optically transparent TFE copolymer is soluble m certan fluorocabons and has the same chemical and oxidative stability as crystallme TFE homopolymers [5]... 

The sorption of water vapor onto nonhydrating crystalline solids below RHq will depend on the polarity of the surface(s) and will be proportional to surface area. For example, water exhibits little tendency to sorb to nonpolar solids like carbon or polytetrafluorethylene (Teflon) [21], but it sorbs to a greater extent to more polar materials such as alkali halides [34-37] and organic salts like sodium salicylate [37]. Since water is only sorbed to the external surface of these substances, relatively small amounts (i.e., typically less than 1 mg/g) of water are sorbed compared with hydrates and amorphous materials that absorb water into their internal structures. 

Teflon AF A Family of Amorphous Fluoropolymers with Extraordinary Properties... 

Since the discovery of Teflon by Roy Plunkett in 1937 a number of fluorinated plastics have reached commercial status. These plastics, exemplified by polytetrafluoroethylene (PIPE), have outstanding electrical, chemical, and thermal properties. AU these commercial materials are either crystaUine or semicrystalline. Teflon AF is a family of amorphous copolymers that retain the desirable electrical, chemical, and thermal properties of semicrystalline fluorinated plastics and also have such properties associated with amorphous materials as optical clarity, improved physical properties, and solubility in selected fluorinated solvents. 

The Teflon AF family consists of copolymers of tetrafluoroethylene, (TFE) and 2,2-bis-trifluoromethyl-4,5-difluoro-l,3-dioxole, (PDD), whose structure is shown in Figure 2.1. The properties of these amorphous copolymers vary with the relative amounts of the comonomers. At present the two commercial grades of Teflon AF are AF-1600 and AF-2400 with glass transition temperatures of 160 and 240°C respectively. The variation of glass transition temperature with composition is shown in Figure 2.2. Thus AF-1600 and AF-2400 contain 64 and 83 mol % PDD, respectively. 

Amorphous polymers characteristically possess excellent optical properties. Unlike all the other commercially available fluoropolymers, which are semicrystalline, Teflon AF is quite clear and has optical transmission greater than 90% throughout most of the UV, visible, and near-IR spectrum. A spectrum of a 2.77-mm-thick slab of AF-1600 is shown in Figure 2.5. Note the absence of any absorption peak. Thin films of Teflon AF have UV transmission greater Ilian 95% at 200 mm and are unaffected by radiation from UV lasers. The refractive indexes of Teflon AF copolymers are shown in Figure 2.6 and decrease with increasing FDD content. These are the lowest refractive indexes of any polymer family. It should be noted that the abscissa could also be labeled as glass transition temperature, Tg, since Tg is a function of the FDD content of the AF copolymer. Abbe numbers are low 92 and 113 for AF-1600 and AF-2400. 

Teflon AF is truly a family of amorphous fluoropolymers with an extraordinary combination of properties. All of the excellent properties of die existing fluoropolymers have either been retained or improved upon and properties arising from the amorphous nature and the presence of microvoids in the AF family of polymers have been added. The similarities and differences of AF and other Teflon polymers are summarized in Table 2.3. This unique combination of properties of Teflon AF amorphous fluoropolymers makes them well suited for applications that had previously precluded polymeric materials,... 

Teflon AF amorphous Teflon or copolymer of PTFE and 2,2-bis(trifluoro-methy l)-4,5-difluoro-1,3-dioxide Teryl 2,4,6-trinitrophenyl-iV-methylnitramine TFA trifluoroacetic acid TGF temperature gradient focusing TGGE temperature gradient gel electrophoresis Ti titanium... 

FEP and PFA despite being melt-processible are crystalline (between 50 and 70%). The crystallinity results in poor optical properties (low clarity) and a very poor solubility in organic solvents. The latter makes the preparation of thin optical coatings exceedingly difficult.10 TEFLON AF, an amorphous fluoropolymer, contains in its molecule a bulky dioxole ring, which hinders crystallization. As a result, the polymer has an exceptionally high clarity and excellent optical properties. Its refractive index is the lowest of any plastic.11... 

Resnick, P. R. and Buck, W. H., Teflon AF Amorphous Fluoropolymers, in Modem Fluoropolymers (Scheirs, J., Ed.) John Wiley Sons, New York, Chapter 22 (1997). 

Teflon AF copolymers have a perfluorinated structure as do FIFE, PFA, and FEP, and therefore they exhibit similar high-temperature stability, chemical resistance, low surface energy, and low water absorption. Unlike FIFE, PFA, and FEP, which are semicrystalline, the completely amorphous Teflon AF copolymers differ considerably in that they are soluble in several perfluorinated solvents at room temperature and have high optical transmission across a broad wavelength region... 

The process of radical recombination in teflon was investigated in details in (23). The recombination has been studied both for initial fluoro-alkyl radicals and for the peroxide ones, which are formed by interaction of initial radicals with oxigen. It has been found that the recombination reaction in teflon can be described by a bimolecular law assuming that the recombination rate in the amorphous state is higher than in the crystalline (samples of various degrees of crystallinity have been studied). The rate constants of recombination have been determined both for the peroxide and fluoro-alkyl radicals. These constants are following (for a sample of 46% crystallinity) ... 

Amorphous carbon nanotube (a-CNT) brushes were prepared by the following procedure.12 Polycarbonate membranes with a pore diameter of 220 nm were soaked in 22 mL of a 0.5 M aqueous solution of glucose in a 25 mL Teflon-lined autoclave. The same procedure was repeated with polycarbonate... 

Bis(trifluoromethyl)-4,5-difluoro-l,3-dioxole represents the monomer of a new family of amorphous fluoropoiymers (Teflon AF, DuPont) with unusual properties [89JFC(45)100]. Novel fluorinated 2,2-bis(triflu-oromethyl)dioxolanes containing alkyne groups have been synthesized from hexafluoroacetone and propargylic alcohol, bromomethyloxirane, or 1,2-bis(bromomethyl)oxirane [90MI1 91JFC(52)I59] (Scheme 95). 

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