Fluorinated hydrocarbon elastomers

Peduoropolyethers, which constitute special class of fluoropolymer, are useful as lubricants,1 elastomers,2 and heat-transfer fluids under demanding conditions. Several commerical products are available, which are generally prepared by ring-opening polymerization of hexafluoropropylene oxide or by the random copolymerization oftetrafluoroethylene and hexafluoropropylene with oxygen under ultraviolet irradiation.3 Direct fluorination of hydrocarbon ethers has been reported4 but must be done very slowly under carefully controlled... 

Uses Solvent for elastomers, natural rubber, synthetic rubber heat-transfer liquid transformer and hydraulic fluid wash liquor for removing C4 and higher hydrocarbons sniff gas recovery agent in chlorine plants chemical intermediate for fluorinated lubricants and rubber compounds fluid for gyroscopes fumigant for grapes. Not produced commercially in the U.S. 

The incorporation of polar groups in unvulcanized polymers reduces their solubility in benzene. Thus the copolymer of acrylonitrile and butadiene (NBR), polychlorobutadiene (Neoprene), and fluorinated EP (the copolymer of ethylene and propylene) are less soluble in benzene and lubricating oils than the previously cited elastomers. Likewise, silicones and phosphazene elastomers, as well as elastomeric polyfluorocarbons, are insoluble in many oils and aromatic hydrocarbons because of their extremely low solubility parameters (silicons 7-8 H polytetrafluoroethylene 6.2 benzene 9.2 toluene 8.9 pine oil P.6). 

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This structure is similar to that of the copolymer TFE and ethylene, except that the random onentation of the methyl group from nonstereospeciftc free radical copo-lymenzation of propylene affords a noncrystalline structure [35] The relatively low fluorine content (54%) of these elastomers compared with VDF-based elas tomers (66-69 5%) makes them significantly less resistant to swelling by hydrocarbons Because of strict alternation, these elastomers have a relatively high glass transition temperature ( 2 °CJ and consequently limited low temperature properties Furthermore, they must be polymerized with a cure site monomer or receive a postpolymerization treatment to adequately activate them for vulcanization [36] To counteract the limited cure response, low-temperature flexibility, and hydrocarbon resistance, these polymers have also been modified with substantial amounts (ca 35 wt %) of VDF [37, 38] This provides some improvements but inevitably decreases the resistance to bases and polar solvents... 

Fluoroelastomers based on TFE and propylene (e.g., AFLAS) (see Section 5.1.1) swell to a high extent in aromatic hydrocarbons because of the relatively low fluorine content (54%). However, because of the absence of VDF in their structure, they exhibit a high resistance to highly polar solvents such as ketones, which swell greatly all fluoroelastomers containing VDF. In addition, elastomers based on copolymers... 

As pointed out earlier, fluorocarbon elastomers are highly resistant to hydrocarbons, chlorinated solvents, and mineral acids. Vulcanizates from them swell excessively in ketones and in some esters and ethers. They also are attacked by amines, alkali, and some acids, such as hot anhydrous hydrofluoric acid and chlorosulfonic acid [9]. Generally, stability and solvent resistance increase with increasing fluorine contents, as shown in Table 5.3. 

FKM elastomers are fluorine-containing hydrocarbon polymers with a saturated structure obtained by polymerizing fluorinated monomers such as vinylidene fluoride, hexafluoropropene, and tetrafluoroethylene. In addition to being able to operate at elevated temperatures they are also generally serviceable in dynamic applications down to — 10°F (—23°C). Thickness of material determines the flexibility at low temperatures, i.e., the thinner the material the more flexible. The brittle point at a thickness of 0.075 in. (1.9 mm) is in the neighborhood of —50°F (—45°C). Depending on the thickness and hardness of the material this temperature can have a range of —25 to -75°F (-32 to -59°C). 

Silicone elastomers are unaffected by oxygen and ozone on natural aging. Because of their water-repellency, silicone elastomers are not seriously affected by aqueous solutions of most chemical reagents. They are attacked by strong acids and alkalis. General purpose elastomers are swollen by aliphatic, aromatic and chlorinated hydrocarbons but much improved resistance is shown by nitrile-and fluorine-containing silicones. In general, room temperature-cured materials have lower solvent resistance. 

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