Specific compounds include a copolymer of 1H,1H-perfluorooctyl methacrylate and cyclohexyl methacrylate and a copolymer of 1H,1H,2H,2H-perfluorodecyl acrylate and cyclohexyl methacrylate; preferably a compound represented by formula (2) having the repeating units of 1H,1H,2H,2H-perfluorodecyl acrylate and of cyclohexyl methacrylate. where n is an integer of 2 or more.