An aromatic functional fluid, specifically a monoalkylated tetradecyl diphenyl oxide synthetic lubricant, contains a polymer-supported reaction product of an organic quaternary ammonium salt, derived from a mercapto-heterocycle and a quaternary ammonium salt. To produce the polymer-supported organic quaternary ammonium salt, the salt is reacted with a dicarboxylic acid or anhydride, specifically 2-dodecen-1-ylsuccinic anhydride. An arylamine antioxidant, such as alkylated phenyl naphthylamine, can be added to the polymer supported organic quaternary ammonium salt-treated functional fluid to impart extra antioxidant and stability properties.