Perfluoropolymers

FEP contains CFj side groups due to copolymerisation with 10-12% hexafluoropropylene. The side groups tend to lock together and improve mechanical properties at processable molecular weights. FEP can be processed by extrusion, and its creep performance is better than that of PTFE. However steric stress due to the bulky side group reduces the CUT from 260 to 200 °C. PFA introduces a perfluoroalkoxy side chain - typically OC3F7. PFA can be injection moulded. Both PFA and FEP have PTFE-like chemical resistance and 

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The discovery of PTFE (1) in 1938 opened the commercial field of perfluoropolymers. Initial production of PTFE was directed toward the World War II effort, and commercial production was delayed by Du Pont until 1947. Commercial PTFE is manufactured by two different polymerization techniques that result in two different types of chemically identical polymer. Suspension polymerization produces a granular resin, and emulsion polymerization produces the coagulated dispersion that is often referred to as a fine powder or PTFE dispersion. 

Like other perfluoropolymers. Teflon PFA is not highly resistant to radiation (30). Radiation resistance is improved in vacuum, and strength and elongation ate increased more after low dosages (up to 30 kGy or 3 Mrad) than with FEP or PTEE. Teflon PEA approaches the performance of PTEE between 30 and 100 kGy (3—10 Mrad) and embrittles above 100 kGy (10 Mtads). At 500 kGy (50 Mrad) PTFE, FEP, and PFA ate degraded. The effect of radiation on tensile strength and elongation is shown in Table 7. 

It is a well-known fact that the mechanical properties of fluoropolymers, especially perfluoropolymers, degrade dramatically under irradiation. Nevertheless a considerable improvement of the mechanical properties of the final grafted copolymers was observed in comparison with mechanical properties of the initial irradiated fluoropolymer. Thus it is possible to minimize or completely avoid the degradation of mechanical properties of the final grafted composites in comparison with the initial fluoropolymers by choosing appropriate reaction conditions. 

Lee KP, Seidel WC Pulmonary response to perfluoropolymer fume and particles generated under various exposure conditions. Fundam Appl Toxicol 17 254—269, 1991... 

Perfluoropolymers have an extremely low degree of intermolecular inter-achon. Thus, the entropy of mixing is the dominant driving force for solubihty. Fluids that have even weak enthalpic interachons with themselves are poorer solvents for perfluoropolymers. For example, aromahe and other unsaturated perfluorocarbons are poorer solvents than their saturated counterparts. Using... 

Table 14.1. Molecular Structure and Properties of Amorphous and Semicrystalline Perfluoropolymers...

The absorption of water and solvents by perfluoropolymers is in general very low.57 Permeability is closely related to absorption and depends on temperature,... 

The carbon chain is in a planar zigzag orientation and forms an orthorhombic lattice with interpenetration of adjacent chains.61 As a result of this structure, ETFE has an exceptionally low creep, high tensile strength, and high modulus compared to other thermoplastic fluoropolymers. Interchain forces hold this matrix until the alpha transition occurs at about 110°C (230°F), where the physical properties of ETFE begin to decline and more closely resemble perfluoropolymers properties at the same temperature. Other transitions occur at -120°C (-184°F) (gamma) and about -25°C (-13°F) (beta).62... 

ETFE copolymers can be readily fabricated by a variety of melt-processing techniques.19 They have a wide processing window, in the range 280 to 340°C (536 to 644°F) and can be extruded into films, tubing, and rods or as thin coating on wire and cables. Injection molding of ETFE into thin sections is considerably easier than injection molding of melt-processible perfluoropolymers because the former has... 

Aqueous dispersions of these two melt-processible perfluoropolymers are processed in a way similar to PTFE dispersion. FEP dispersions can be used for coating fabrics, metals, and polyimide films. They are very well suited for bonding seals and bearings from PTFE to metallic and nonmetallic components and as nonstick and low-friction coatings for metals.16 FEP can be fused completely into a continuous film in approximately 1 min at 400°C (752°F) or 40 min at 290°C (554°F).17 PFA is used to coat various surfaces, including glass fabric, glass, and metals. 

The main application of amorphous perfluoropolymers is as cladding of optical fibers, antireflective coatings, low dielectric coatings, and in the electronic industry (e.g., photoresists)1012 and as a low-dielectric-constant insulator for high-performance interconnects.13... 

Takata, H. et al. (2007), Adsorption Properties of Water Vapor on Sulfonated Perfluoropolymer Membranes , International Journal of Hydrogen Energy, 32, 371-379. 

Electrochemical Characterization of Ferrocene Derivatives in a Perfluoropolymer Glucose Oxidase Electrode... 

General. There is no doubt that a comparison (updated in the 1990s) of the potential vs. current density plot for the various fuel cells (see Fig. 13.27) shows that the proton exchange membrane fuel cell with a perfluoropolymer sulfuric acid has superior performance (i.e., higher cell potential and hence efficiency) compared with the other types of fuel cells. Because this cell has been chosen for development by the majority of the automotive manufacturers, special attention is given here to its development. 

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