wherein R is an alkyl group having 1 to 32 carbon atoms, a polyfluorocarbon group or a perfluoropolyether group; R' is an alkylene group having 1 to 6 carbon atoms, a phenylene group, an oxyphenylene group or a sulfonamide group; M is an alkali metal; and n is 0 or 1, gives oil filter-gaskets having a distinguished durable protection against fixation without lowering of high temperature sealabilit