Perfluoroelastomers have achieved outstanding commercial success and are used in a wide variety of applications in which severe environments are encountered, in particular those end uses where exposure to high temperatures and aggressive chemicals occurs. These polymers are often used in seals for aircraft engines, in oil-well drilling devices, and in sealing elements for industrial equipment used at high temperatures.
The outstanding properties of perfluoroelastomers are largely attributable to the stability and inertness of the copolymerized perfluorinated monomer units that make up the major portion of the polymer backbones of these compositions. Such monomers include tetrafluoroethylene and perfluoro(alkyl vinyl) ethers. In order to develop elastomeric properties fully, perfluoroelastomers are typically crosslinked, i.e. vulcanized. To this end, a small percentage of cure site monomer is copolymerized with the perfluorinated monomer units. Cure site monomers containing at least one nitrile group, for example perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene, are especially preferred. Such compositions are described in U.S. Pat. Nos. 4,281,092; 4,394,489; 5,789,489; and 5,789,509.
Curing systems which incorporate tetraphenyltin have been successfully used to vulcanize nitrile-containing perfluoroelastomers, however, the cure rate of such compositions is too slow for economically effective commercial production of perfluoroelastomer articles in certain instances. Logothetis and Schmiegel, in U.S. Pat. No. 5,677,389, disclose the use of ammonium salts as accelerators for use in a variety of curing systems useful with perfluoroelastomers. Curable compositions containing the ammonium salts exhibit enhanced cure rate, but in some instances certain ammonium salt accelerators are not effective because of insolubility in the polymer. In addition, organometallic compounds are expensive. It would therefore be beneficial to have an alternative means for enhancing the cure rate of perfluoroelastomers which does not depend on the use of ammonium salt accelerators or require the use of organometallic compounds.
USPTO Backgrounds
USPTO Backgrounds