Radio-frequency plasma polymer and copolymer films, ranging in thickness from 9 to 660 nm, were prepared from perfluoroallylphosphonic acid (PAPA) and chlorotrifluoroethylene (CTFE). ac conductance measurements showed that the apparent conductivity of the films increased from 1.7 to 4.2 mS/cm as the PAPA content of the comonomer feed was increased from 0 to 100%. Cyclic voltammetry in the presence of chloride indicated that the films were anionic and showed that they were strongly adherent to gold electrodes in aqueous media. As the PAPA content of the comonomer feed was increased, the advancing water contact angle of the films decreased from 98.4 degrees to 8.3 degrees and the solid surface tension (gamma(s)) of the films increased from 25.4 to 72.5 dyn/cm. High-resolution ESCA and FTIR spectroscopies indicated that increasing the PAPA content of the comonomer feed caused a change in the polymer structure from a highly fluorinated, lightly cross-linked Teflon-like structure to a lightly fluorinated, highly cross-linked structure containing phosphonic acid groups. A mechanism for the formation of the ionic polymer films is proposed in which retention of the phosphonic acid moiety occurs via cleavage of PAPA into fluorocarbon and phosphonate fragments followed by reincorporation of the phosphonic acid into the growing plasma polymer film.