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There are many kinds of lubricants such as automatic transmission fluid, brake fluid, bearing grease, etc. used in automotive vehicles. Fluoroelastomers have been used for a long time for oil seals contacting such lubricants. Fluoroelastomers composed of vinylidene fluoride, hexafluoropropylene, and optionally incorporated tetrafluoroethylene are designated as FKM, which have been one of the most popular fluoroelastomers. The latest automotive lubricants tend to contain a large amount of additives to improve the performance along with the demanding driving conditions. Such additives, however, are reactive with FKM at elevated temperatures to raise the hardness of FKM, which results in losing the sealing performance. An elastomer material which does not lose the flexibility in the long-term exposure to the lubricant has been desired.

FEPM alternating dipolymers of tetrafluoroethylene (TFE) and propylene (P) are well known to exhibit distinguished chemical resistance, especially against various organic and inorganic bases, compared to conventional fluoroelastomers (FKM): e.g., copolymers of vinylidene fluoride (VdF), hexafluoropropylene (HFP), and optionally incorporated tetrafluoroethylene (TFE). These unique characteristics have been finding automotive sealing applications where lubricants formulated with considerable quantity of additives are used. FEPM dipolymers, however, have difficulty in processing - particularly in mold release. There are TFE-P-VdF terpolymers available, which are improved in mold release. TFE-P-VdF terpolymers, however, are often pointed out that the base resistance is lost to some extent, because the minimum quantity of VdF necessary to establish a practical cure speed and physical properties is not very low.