PEEK linear monodisperse oligomers have been synthesized by an iterative two-step route. Nucleophilic substitution of the fluorine end groups of a fluoroaryl ketone-ended n-mer by p-phenoxyphenol in the presence of sodium carbonate yielded a phenoxy-ended n-mer. Then a Friedel-Crafts acylation of the terminal phenyls of this compound was performed using 4-fluorobenzoic acid as the acylating agent in the superacid solvent CF3SO3H to obtain a fluoroaryl ketone-ended (n + 2)-mer. A simple kinetic analysis of the electrophilic reaction is performed with the aid of F-19 NMR. A side reaction was detected for strong reagent dilution. Various spectroscopic results indicate that this side reaction is due to the presence in solution of protonated ketones, which act as electrophiles competing with the acylating agent. The results of the kinetic analysis support a mechanism in which the acylium cation (or a protonated mixed anhydride) is the acylating agent. Spectroscopic characterization of the oligomers confirms the expected structures.