Polymer 194 (2020) 122346 Available online 19 March 2020 0032-3861/© 2020 Elsevier Ltd. All rights reserved. Polymer conjugates for dual functions of reporting and hindering corrosion Naruphorn Dararatana , Farzad Seidi , Daniel Crespy * Department of Materials Science and Engineering, School of Molecular Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), Rayong, 21210, Thailand A R T I C L E INFO Keywords: Controlled release Corrosion Fluorescent sensor pH-responsive Smart coating ABSTRACT Corrosion is still globally a major fnancial challenge and requires new materials development so that energy and resources can be saved more effectively. Suitable advanced coatings for metals shall frst hinder corrosion. When corrosion still occurs, the coating shall emit a signal to allow timely maintenance before metallic structure is too much damaged. We prepared copolymers that can release corrosion inhibitors, 5-(aminomethyl)-8-hydrox- yquinoline (AM8HQ) and benzotriazole (BTA), upon acidic hydrolysis of imine and hemiaminal ether linkages. Furthermore, a fuorescent molecule is attached to the copolymer via thiopropionate groups. Hydrolysis of the latter group and release of the fuorescent sensor occurs after release of the inhibitors. Corrosion rates of steel substrates coated with the pH-responsive polymers are dramatically reduced and fuorescence are detected upon onset of corrosion. 1. Introduction In 2015, total global costs of corrosion exceeded 2.5 trillion US dollars [1]. Moreover, corrosion of metals can induce environmental pollution and mortal accidents due to materials failure. Therefore, anticorrosion and corrosion detection are desirable properties for extending service life of metallic structures. Effective and cost-effcient strategy to prevent corrosion of metal is provided by coating metals with organic, inorganic, or hybrid materials with good barrier properties against water and oxygen [2]. Smart coatings, which can sense and respond to environmental stimuli such as mechanical damage, temper- ature, and chemical changes were developed for anticorrosion applica- tions [3–7]. They can be classifed by their actions such as self-healing, self-cleaning, or corrosion detection. Stimuli-responsive materials were prepared to release corrosion inhibitors upon physical damage [8,9], redox signal [10,11], and pH change [12–14]. Polyelectrolytes nano- particles, nanocontainers, and microparticles were prepared by the layer-by-layer technique [15–17], sol-gel processes [18–24], polymeri- zations in dispersed media [25,26], or supramolecular chemistry [27–29] to entrap corrosion inhibitors or other compounds [30,31]. These materials were then embedded in conventional coatings. Although anticorrosion performance was signifcantly enhanced, the transfer of lab results to practical applications remain critical [32]. Another approach is to prepare coatings that release corrosion in- hibitors upon cleavage of labile bonds that are sensitive to change of pH value or redox conditions. This strategy avoids early leaching of in- hibitors in the environment in non-corrosive conditions. Reduction reaction during corrosion process of metal can be applied as trigger to control the release of corrosion inhibitors from polymers. Tryptamine, a corrosion inhibitor, was attached to a polymer via disul- fde linkage to form poly [n-butyl methacrylate-co-((2-((tryptamine carbamoyl)oxy)ethyl) disulfanyl) ethyl methacrylate] [11]. The inhibi- tor could be released from polymer flms in the presence of a reducing agent. The corrosion inhibitor 2,5-dimercapto-1,3,4-thiadiazole was also released upon reduction by depolymerization of polymer nano- particles [10]. Moreover, another effective stimulus to regulate the release of corrosion inhibitors is the change of acidity, which results from the redox reaction at anodic area during corrosion of metal [12]. A bisacrylate derivative of 4-(2-pyridylazo)resorcinol, a corrosion inhibi- tor for copper, was copolymerized in the main chain of polymers by thiol-ene polymerization [14] The obtained polymers contained acid responsive β-thiopropionate linkages so that the inhibitor could be released in mild acidic medium (pH ~ 3.5) [14]. However, even in the presence of anticorrosion materials, corrosion still occurs after a suffciently long time or in harsh conditions. There- fore, corrosion detection is also an important feature which is suitable in coatings for metals. Detection based on optical changes is a simple method to evaluate of metals start to corrode. Dhole et al. modifed an acrylic polymer with 5-acrylamido-1,10-phenanthroline to detect the formation of Fe 2þ upon oxidation of mild steel. Color of the coating * Corresponding author. E-mail address: daniel.crespy@vistec.ac.th (D. Crespy). Contents lists available at ScienceDirect Polymer journal homepage: http://www.elsevier.com/locate/polymer https://doi.org/10.1016/j.polymer.2020.122346 Received 26 December 2019; Received in revised form 27 February 2020; Accepted 29 February 2020