Patent ID: 8492320

Claim:
A method for improving heat resistance of a lubricating oil including at least a perfluoropolyether oil represented by the following General Formula (A), comprising the steps of: preventing decomposition of the perfluoropolyether oil at high temperatures by adding a fluorine-containing diamide compound represented by the following Formula (I) in the range of 0.5 to 5 wt % based on the lubricating oil, dissolving it in the perfluoropolyether oil and making a solution: RfO(CF 2 CF 2 O) j (CF 2 O) k Rf General Formula (A); wherein, Rf represents a perfluoro lower alkyl group having 1 to 5 carbon atoms, j+k=3 to 200, and j:k=10:90 to 90:10, and each repeating unit is randomly bonded; wherein, Y represents an oxygen atom (O), sulfur atom (S), CO group, SO group, or SO 2 group; k is an integer of 1 to 5; m is an integer of 1 to 2; and n is an integer of 11 to 40; and wherein substituting positions of two substitutional groups possessed by each phenyl group may be any one of an ortho-position, meta-position, and para-position.