Synthesis of Poly(p-phenylene diamine) and Its Corrosion Inhibition Effect on Iron in 1M HCl P. Manivel, 1 S. Sathiyanarayanan, 2 G. Venkatachari 2 1 A. C. College of Engineering and Technology, Karaikudi 630 004, India 2 Central Electrochemical Research Institute, Karaikudi 630 006, India Received 9 August 2007; accepted 26 May 2008 DOI 10.1002/app.28772 Published online 27 August 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Water-soluble poly(p-phenylene diamine) was chemically synthesized. Its corrosion inhibition per- formance was evaluated for iron corrosion in 1M HCl at various concentrations, and the results were compared with that of the monomer. The corrosion inhibition prop- erties were evaluated by polarization techniques and elec- trochemical impedance spectroscopy. The results showed that poly(p-phenylene diamine) was a more efficient corro- sion inhibitor than the monomer and gave an 85% inhibi- tion efficiency at a concentration of 50 ppm, whereas the monomer gave an efficiency of 73% at 5000 ppm. V V C 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2807–2814, 2008 Key words: adsorption; conjugated polymers; FT-IR INTRODUCTION The inhibition of corrosion in metals is of high tech- nological importance, 1 and progress made in this field has been phenomenal in last few decades. 2,3 Acids find immense applications in pickling, clean- ing, descaling, and so on. To avoid base-metal attack and to ensure the removal of corrosion products/ scales alone, inhibitors are used extensively. The selection of appropriate inhibitors mainly depends on the type of acid, its concentration, temperature, velocity, presence of dissolved solids, and type of metallic materials involved. An important criterion in the characterization of the efficiency of inhibitors is their efficiency/concentration ratio. Schmitt, 4 in his review, discussed extensively the types of inhibitors recommended for the protection of metallic materi- als, especially ferrous metals and alloys, from corro- sion in acid solutions during picking, acid cleaning, scale removing, and oil and gas well acidizing. The important prerequisites for a compound to be an efficient inhibitor are (1) it should form a defect- free, compact barrier film; (2) it should chemisorb on to the metal surface; (3) it should be polymeric or poly- merize in situ on the metal; and (4) the barrier thus formed should increase the inner layer thickness. Compounds containing nitrogen, sulfur, and oxygen have been established as good inhibitors for iron in acidic media. 5 Organic compounds having p bonds are found to inhibit corrosion steel by getting adsorbed over the electrode surface through electron sharing. 6 The presence of functional groups such as ¼¼NH, AN¼¼NA, ACHO, RAOH, and R¼¼R in the inhibitor molecule 7,8 and also the steric factors, aromaticity, and electron density at the donor atoms have been found to influence the adsorption of the inhibitor molecule over the corroding electrode surface. The role of the molec- ular area 9 and molecular weight 10 of the organic mole- cule on its inhibition efficiency has also been reported. Various organic compounds, such as amines, acety- lenic alcohols, and heterocyclic compounds, have been in use as inhibitors in industry. 11–15 In recent days, polymers 16 and conducting polymers 17–22 have attracted a great deal of attention because of their wide range of industrial applications and economics. Because of the presence of extensive delocalization of p electrons, these polymers could serve as better cor- rosion inhibitors at very low concentrations. Earlier studies 23–26 showed that substituents such as AOCH 3 , ACOOH, and ACH 3 present in polyaniline have a significant influence on the corrosion inhibitive prop- erties for iron in 1M HCl. The order of inhibitor per- formance has been found to be Poly(p-anisidine) > Poly(p-amino benzoic acid)  Poly(p-toludene) > Poly- aniline. In this article, the effect of the NH 2 group on the corrosion inhibition of polyaniline for iron in 1M HCl is presented. EXPERIMENTAL Chemical synthesis of water-soluble poly(p-phenylene diamine) (PPD) Reagent-grade p-phenylene diamine was used for the preparation of water-soluble PPD. A fresh 0.1M Journal of Applied Polymer Science, Vol. 110, 2807–2814 (2008) V V C 2008 Wiley Periodicals, Inc. Correspondence to: G. Venkatachari (gvchari@gmail.com).