The reaction of electrode-confined polyaniline with trifluoroacetic anhydride in acidified acetonitrile giving insulating and electroinactive trifluoroacetylated polyaniline has been studied by electrochemistry, reflectance IR, and microelectrochemistry. Variation of electrochemical. potential from 0.2 V (reduced, most reactive) to 0.6 V (oxidized by 0.5 electron per repeat unit, unreactive) vs SCE allows control of the reaction rate. Reaction of trifluoroacetic anhydride with aniline oligomers N-phenylphenylenediamine and N,N’-diphenylphenylenediamine gave N-trifluoroacetylation products exclusively, exhibiting positive shifts in oligomer oxidation potential of >0.5 V, with terminal amines reacting considerably faster than internal amines. Reflectance IR following the potential-dependent growth of CO and CS peaks for macroelectrode films of polyaniline treated with trifluoroacetic anhydride showed similar potential dependence of reactivity as conductivity measurements during trifluoroacetylation of polyaniline-derivatized microelectrode arrays. Polyaniline trifluoroacetylation was accompanied by narrowing but no shifting of the potential window of electroactivity and conductivity, and eventual elimination of all conductivity. Trifluoroacetylation of polyaniline terminal amines, rapid at all potentials, does not detectably affect conductivity. Also examined by electrochemistry were the reactions of polyaniline with other anhydrides resulting in the reactivity order (F3CCO)(2)O > (Cl3CCO)(2)O > (H2ClCCO)(2)O > (HCl2CCO)(2)O >> (H3CCO)(2)O. IR through polyaniline electrodeposited onto optically transparent Au electrodes shows that essentially complete loss of polyaniline electroactivity occurs when approximate to 25% of nitrogens are trifluoroacetylated. Electroactivity and conductivity of trifluoroacetylated polyaniline may be recovered by hydrolysis in K2CO3/CH3OH/O-2 solution to regenerate polyaniline. Use of the reversible trifluoroacetylation of polyaniline provides a proof-of-concept for a new approach to an erasable-programmable-read-only-memory device.