Fluoroelastomers

The importance of fluorine in polymer chemistry has been known since the discovery of poly (tetrafluoroethylene) in 1938. Highly fluorinated polymers are very stable and have remarkable resistance to oxidative attack, flame, chemicals, and solvents. This stability has been attributed to the strength of the carbon—fluorine bond compared to that of the carbon—carbon bond, to steric hindrance, and to strong Van der Waals forces. The synthesis of elastomeric polymers containing enough fluorine to impart a significant degree of stability was not achieved until the mid-1950's. Since then a multitude of fluoroelastomers have been reported, but, of these, only certain copolymers of vinylidene fluoride, and fluorosilicone polymers have become commercially important. Recently, however, perfluoroelastomers based on perfluoro (alkyl vinyl ethers) and tetrafluoroethylene have been shown to possess an even greater degree of high temperature stability than do the fluoroelastomers hitherto available. These perfluoroelastomers also are essentially inert to most chemicals and solvents. Copolymers of perfluoro (alkyl vinyl ethers) with partially fluorinated monomers also have been developed that give better flexibility at low temperature. These polymers, now at the developmental stage, appear to be the forerunners of a new generation of superior high-performance elastomers. The discussion that follows will concern firstly, the commercial fluoroelastomers; secondly, those that show commercial promise and might be considered semi-commercial or at the developmental stage but which are available only in limited developmental quantities; and thirdly, those reported in the literature that, so far at least, have been of research interest only. In this last category, polymers will not be included which contain so little fluorine that performance characteristics are not substantially enhanced. For example fluoroprene [poly(2-fluorobutadiene)] and copolymers with nonfluorinated, olefin monomers in which the latter predominate will not be included.