Containing Perfluoro Methyl Vinyl Ether

COPOLYMERS CONTAINING PERFLUORO(METHYL VINYL ETHER) 

In order to maintain the underlying excellent thermal, chemical and oxidative resistance of the basic copolymer, to avoid complications such as chain transfer during polymerization and to facilitate processing, the requirements of the cure-site monomer become stringent. It has been found that in principle perfluorovinyl ethers of the type indicated below most nearly fulfil these requirements  

Promising results were obtained using perfluoro(2-phenoxypropyl vinyl ether) at about 2 mole%  

Vulcanization may be brought about by amines such as tetraethy-lene pentamine and hexamethylene diamine carbamate. It is believed that the process involves reaction of the diamine with the para fluorine atom on the aromatic ring  

Magnesium oxide is present to react with the hydrogen fluoride formed as described in the previous section. In addition, as with the more established fluoroelastomers, a long post-cure process is required to expel the water formed. 

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In attempts to further improve the stability of fluorine-containing elastomers Du Pont developed a polymer with no C—H groups. This material is a terpolymer of tetrafluoroethylene, perfluoro(methyl vinyl ether) and, in small amounts, a cure site monomer of undisclosed composition. Marketed as Kalrez in 1975 the polymer withstands air oxidation up to 290-315°C and has an extremely low volume swell in a wide range of solvents, properties unmatched by any other commercial fluoroelastomer. This rubber is, however, very expensive, about 20 times the cost of the FKM rubbers and quoted at 1500/kg in 1990, and production is only of the order of 1 t.p.a. In 1992 Du Pont offered a material costing about 75% as much as Kalrez and marketed as Zalak. Structurally, it differs mainly from Kalrez in the choice of cure-site monomer. 

Many other crosslinking reactions are used in commercial applications. A variety of halogen-containing elastomers are crosslinked by heating with a basic oxide (e.g., MgO or ZnO) and a primary diamine [Labana, 1986 Schmiegel, 1979]. This includes poly(epichlorohydrin) (Sec. 7-2b-6) various co- and terpolymers of fluorinated monomers such as vinylidene fluoride, hexafluoropropene, perfluoro(methyl vinyl ether), and tetrafluoroethylene (Sec. 6-8e) and terpolymers of alkyl acrylate, acrylonitrile, and 2-chloroethyl vinyl ether (Sec. 6-8e). 

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