Electrodeposition of Poly(4-methyl carbazole-3-carboxylic acid) on Steel Surfaces and Corrosion Protection of Steel Meltem Du ¨ du ¨ kcu ¨, 1 Yasemin Arslan Udum, 1 Yavuz Ergu ¨ n, 2 Fatih Ko ¨ leli 1 1 Department of Chemistry, Arts and Science Faculty, Mersin University, 33343 Mersin, Turkey 2 Department of Chemistry, Arts and Science Faculty, Dokuz Eylu ¨ l University, 35160 _ Izmir, Turkey Received 30 November 2007; accepted 7 July 2008 DOI 10.1002/app.29151 Published online 30 October 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The electropolymerization of 4-methyl carba- zole-3-carboxylic acid was successfully performed on a stainless steel (316L) surface with lithium perchlorate/aceto- nitrile as the supporting electrolyte. The corrosion resistance of the new coating, poly(4-methyl carbazole-3-carboxylic acid) (PCz), was investigated. To this end, potentiodynamic polarization curves, open circuit potentials, and electrochem- ical impedance spectroscopy were used to evaluate the capacity of the PCz coating to protect the steel surface. The corrosion tests indicated that PCz exhibited effective anodic protection in a corrosive test solution. V V C 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1496–1500, 2009 Key words: coatings; conducting polymers; synthesis INTRODUCTION Conducting polymers, including polypyrrole, 1–3 poly- aniline, 4–7 polyindole, 8–11 and polycarbazole, 12–14 have been intensively investigated since the late 1970s. Among these polymers, polycarbazoles have been known for their good electroactivity and ther- mal, electrical, photophysical, and electrochromic properties. They have been suggested for a number of applications, such as electroluminescent devices, sen- sors, redox catalysts, and electrochromic displays. 15–18 Protective conducting polymer coatings have been widely used for metal corrosion control. Since Deberry 19 reported in 1985 that polyaniline reduced the corrosion rate of stainless steel (SS) by anodic protection, polyaniline and its derivatives have been used as protective coatings. In 1996, Ahmad and MacDiarmid 20 found that electrochemically synthe- sized polyaniline was able to protect iron and steel. Camalet et al. 21 reported that polyaniline coatings electrochemically deposited from oxalic acid pro- vided good protection to steel in acidic chloride sol- utions. Polypyrrole and its derivatives have also been investigated intensively for their ability to pro- vide corrosion protection. 22–24 Lacaze et al. 25 showed that electrochemically synthesized polypyrrole coat- ings were effective for the corrosion protection of oxidizable metals such as iron, aluminum, and zinc. SSs are of special interest for many applications because of their corrosion resistance. Although the formation of a thin oxide layer is effective for protect- ing SSs, the breakdown of this passive film leads to the initiation and propagation of localized corrosion. 26,27 Carbazole-based polymer systems have structural similarities to polypyrrole and polyaniline; however, no attempts at using polycarbazole and its deriva- tives for corrosion control have been reported in the literature. In this article, we report for the first time the electrochemical polymerization of 4-methyl car- bazole-3-carboxylic acid on an SS electrode and the corrosion behavior of this coating: The aims of this study were first to electrochemi- cally synthesize poly(4-methyl carbazole-3-carboxylic acid) (PCz) on an SS electrode and second to investi- gate the corrosion resistance of the polymer-coated steel with potentiodynamic polarization, open circuit potential/time curves, and electrochemical imped- ance measurements in 3.5% NaCl. EXPERIMENTAL 4-Methyl carbazole-3-carboxylic acid was synthe- sized chemically. The chemical synthesis of the monomer was previously described. 28 Acetonitrile (ACN) and lithium perchlorate (LiClO 4 ) were Journal of Applied Polymer Science, Vol. 111, 1496–1500 (2009) V V C 2008 Wiley Periodicals, Inc. Correspondence to: M. Du ¨ du ¨ kcu ¨ (mdudukcu@mersin.edu. tr).