Chemical synthesis of 1-pyrrolyl-10-decanephosphonic acid (PyDPA) from pyrrole and the electrochemical polymerization of PyDPA in methylene chloride under potentiodynamic and potentiostatic conditions are reported. It is found that the electrochemical window used during polymerization affects the properties of the film. Potentiodynamic polymerization at anodic switching potentials of >1.8 V results in thin (< 0.5 mu m), overoxidized films, analogous to those obtained by overoxidation of polypyrrole. During potentiodynamic polymerization using anodic switching potentials between 1.55 and 1.7 V, the polymer undergoes a conducting-to-insulating transition. The amount of polymer deposited before the onset of passivation is shown to increase with decreasing anodic switching potential; therefore, film thickness, density, and electronic properties can be tuned. Both conducting and insulating films show cation permselectivity when cycling in Ru(NH3)(4)(2+)/Ru(NH3)(4)(3+) but rejection of Fe(CN)(6)(3-)/Fe(CN)(6)(4-), regardless of thickness. Deposition at constant potential results in more reproducible film depositions and greater control over film properties.