Amine-Quinone Polyimides as Coatings that Protect Iron Against Corrosion.
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Amine-Quinone Polyimides as Coatings that Protect Iron Against Corrosion. Mijeong Han, Huimin Bie, Garry W. Warren and David E. Nikles Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama 35487-0209 ABSTRACT A new diamine monomer was synthesized by condensing 4,4’-methylene dianiline with 1,4benzoquinone. The monomer was condensed with 3,3’,4,4’-benzophenone tetracarboxylic dianhydride to give a polyamic acid that was soluble in N-methyl-2-pyrrolidinone. The polyamic acid was cast onto iron and thermally imidized to give the amine-quinone polyimide (AQPI-2). AQPI-2 had a thermal decomposition temperature (10% weight loss) of 540°C and a glass transition near 290°C, values typical of polyimides. The degradation of the coating on iron after exposure to NaCl electrolyte was followed by electrochemical impedance spectroscopy. Under these conditions a conventional polyimide failed after 3 days exposure, while AQPI-2 showed no change after 34 days exposure. The adhesive bond between the amine-quinone polyimide and the iron surface was so strong that it could not be broken by the electrolyte. INTRODUCTION Polymers containing the 2, 5-diamino-1, 4-benzoquinone functional group have been of interest, since this of class polymers have a strong affinity for the surface of iron and can protect iron against corrosion [1,2]. The inhibiting effect was attributed to the abundance of electrons and unshared electrons on the nitrogen atom, which can interact with the d-orbitals of iron to form a coordinate bond. We have synthesized amine-quinone polyurethanes by condensing the amine-quinone diol monomer, 2,5-Bis-(N-2-hydroxyethyl-N-methylamino)-1,4-benzoquinone, and an oligomeric diol monomer (e.g., polytetrahydrofuran diol) with a diisocyanate (e.g., 2,5diisocyanatotoluene) [3,4]. These polyurethanes were shown to inhibit the corrosion of iron [5,6] and to promote adhesion of epoxy to steel [7]. However, these polymers started to decompose at relatively low temperatures, around 200°C, and had low glass transition temperature. In this study, we have synthesized novel amine-quinone dianiline monomer (AQMDA) and amine-quinone polyimide by two-step polymerization. This new polyimide had good thermal stability and a high glass transition temperature. It showed much better corrosion protection on the iron substrate than the conventional polyimide did in aqueous NaCl solution. O
NH2
CH2
N H
H N
CH2
NH2
O
AQMDA
FF5.17.1 Downloaded from https://www.cambridge.org/core. UCSD University of California San Diego, on 22 Jun 2020 at 18:33:16, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-629-FF5.17
EXPERIMENTAL Materials High purity (99.99+) iron squares, 50 mm x 50 mm x 1.5 mm, were purchased from Goodfellow. The iron squares were polished with 240, 320, 400, and 600 silicon carbide grit papers, followed by polishing with 1, 0.3, and then 0.05 µm Al2O3 slurries. All samples were ultrasonically cleaned in isopropanol fo
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