Vinylidene fluoride-hexafluoropropylene elastomers

Ki-aton G1600 SEES Perfluorinated ionomers Phenolic resins Polystyrene, head-to-head Poly(yinyl chloride), head-to-head S tyrene- acrylonitrile Styrene-butadiene elastomers Styrene-methylmethacrylate copolymer Sulfo-ethylene-propylene-diene monomer ionomers Vinylidene fluoride-hexafluoropropylene elastomers Chemigum... 

Trifluoronitrosomethane-tetrafluoroethylene copolymer vulcanizates have outstanding resistance to chemicals, being generally superior to vinylidene fluoride-hexafluoropropylene elastomers. Some fluorinated solvents cause appreciable swelling. 

Vinylidene fluoride-hexafluoropropylene co-polymer (VF2/HFP) n. Any of a family of chemical- and heat-resistant, vulcaniz-able elastomers containing 60-85% VF2 (DuPont s Viton A). Terpolymers with small amounts of tetrafluoroethylene are also available. 

Fig. 3. The percent volume swell in methanol for 7 days at 21°C compared with the weight percent of fluorine in fluorocarbon elastomers 66%, dipolymer of vinyli-dene fluoride-hexafluoropropylene 68% and 70%, terpolymers of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene.

Vinylidene fluoride-hexafluoropropylene copolymer vulcanizates have excellent thermal stability, withstanding long periods at 300°C without serious deterioration. Low temperature performance is limited and the elastomers are not generally suitable for sub-zero use. Applications of the elastomers include seals and hose in contact with fuels and lubricants, pump components and tank linings. 

Perfluoroelastomer (tetrafluoro-perfluoromethyl vinyl ether copolymer) Introduced by DuPont in 1977 as Kalrez , this elastomer combines the properties of a conventional fluoroelastomer, such as vinylidene fluoride-hexafluoropropylene copolymer, with those of a fluorocarbon resin such as polytetrafluoroethylene. It has found application for O-rings and seals that must withstand strong chemicals and solvents at high temperatures. 

Elastomers examined included NR, nitrile rubber, ethylene-propylene dimer and a vinylidene fluoride - hexafluoropropylene copolymer. Examination of migrating species was carried out by methods discussed in the EC Framework Directive 89/109/ EC (see Chapter 16). Distilled water and diethyl ether extractants were included in this study. 

Copolymerization is an important way to produce properties that are not possible with homopolymers. For example, the homopolymer of vinylidene chloride is highly crystalline, and though it has excellent moisture and oxygen barrier properties, it does not produces very strong film or fiber. Copolymerization with 15 percent vinyl chloride disrupts the regular structure of the homopolymer to produce a stronger, clearer, more flexible material. The copolymer retains much of the barrier properties of the homopolymer and finds wide use for food packaging and filament. Other commercial copolymers include styrene-acrylonitrile, discussed above vinylidene fluoride-hexafluoropropylene, a heat- and oil-resistant elastomer styrene-butadiene rubber ethylene-vinyl acetate hot melt adhesive and 2-ethylhexyl acrylate-vinyl acetate-acrylic acid pressure-sensitive adhesives. 

The copolymer of vinyl ferrocene (VF) and butadiene has also been reported in the literature for use as a binder for composite propellants. It does not require any burn-rate (BR) accelerator because of the presence of iron (Fe) in vinyl ferrocene which is converted to finely divided Fe203 (a well-known BR accelerator) during combustion. A few groups of scientists have also studied fluorocarbon polymers as binders for composite propellants because of their excellent compatibility with oxidizers and fuels coupled with high density. Accordingly, Kel-F elastomer (a copolymer of vinylidene fluoride and chlorotrifluoroethylene, trade name of 3M, USA) and Viton-A (copolymer of hexafluoropropylene and vinylidene fluoride, trade name of Du Pont, USA) have also been reported for this purpose. The structures of Kel-F 800 [Structure (4.13)] and Viton-A [Structure (4.14)] are ... 

Fluorocarbon elastomers represent the largest group of fluoroelastomers. They have carbon-to-carbon linkages in the polymer backbone and a varied amount of fluorine in the molecule. In general, they may consist of several types of monomers poly-vinylidene fluoride (VDF), hexafluoropropylene (HFP), trifluorochloroethylene (CTFE), polytetrafluoroethylene (TFE), perfluoromethylvinyl ether (PMVE), ethylene or propylene.212 Other types may contain other comonomers, e.g., 1,2,3,3,3-pentafluropropylene instead of HFP.213 Fluorocarbon elastomers exhibit good chemical and thermal stability and good resistance to oxidation. 

The first commercial fluoroelastomer, Kel-F, was developed by the M. W. Kellog Company in the early to mid-1950s and is a copolymer of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE). Another fluorocarbon elastomer, Viton A, is a copolymer of VDF and hexafluoropropylene (HFP) developed by du Pont was made available commercially in 1955. The products developed thereafter can be divided into two classes VDF-based fluoroelastomers and tetrafluoroethylene (TFE)-based fluoroelastomers (perfluoroelastomers).72 The current products are mostly based on copolymers of VDF and HFP, VDF and MVE, or terpolymers of VDF with HFP and TFE. In the combination of VDF and HFP, the proportion of HFP has to be 19 to 20 mol% or higher to obtain amorphous elastomeric product.73 The ratio of VDF/HFP/TFE has also to be within a certain region to yield elastomers as shown in a triangular diagram (Figure 2.2).74... 

Fluoropolymer elastomers (or Viton, a registered trademark of the DuPont Performance Elastomer LLC) consist of hexafluoropropylene (HFP), vinylidene fluoride (VDF), and tetrafluoroethylene. The 3M Corporation uses the trade name Fluorel. The structures of each of these monomers are shown in Figure 8.14. The fluorine content of these terpolymers is typically around 70% for Viton. Four basic types of this material are shown in Table 8.8 however, Viton Extreme comprises more types. 

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