pH-Sensitive Polymer Conjugates for Anticorrosion and Corrosion Sensing

In 2015, the global cost of corrosion in the world was estimated to be around 2.5 trillion dollars and has been continuously increasing. The active protection by corrosion inhibitors is a well-known technique for protecting metals against corrosion. However, one major disadvantage is that corrosion inhibitors can be leached in the environment, even when corrosion does not occur. We design and synthesize smart polymer/corrosion inhibitor conjugates as a new generation of materials for corrosion protection. These materials release inhibitors upon acidification, which may occur either by acidic rain or as a consequence of the metal corrosion process itself. A polymerizable derivative of 8-hydroxyquinoline (8HQ), an effective corrosion inhibitor, is prepared so that it contains acid-labile beta-thiopropionate linkages. The monomer is copolymerized with ethyl acrylate, and the obtained functional polymer is processed to form nanoparticles. Under acidic conditions, >95% 8HQ is released from the nanoparticles of the polymer conjugates after 14 days. However, the release was significantly slower under neutral conditions, reaching only 15% during the same period. Additionally, nonconjugated 8HQ can be physically entrapped in the nanoparticles of the polymer conjugates by encapsulation. The nonconjugated 8HQ is then released in less than 30 min so that the coexistence of both conjugated and nonconjugated 8HQ in the nanoparticles allows a release profile, which is a hybrid of sustained and burst releases. Furthermore, the nanoparticles are advantageously used as nanosensors. The 8HQ released from the nanoparticles displays enhanced fluorescence upon chelation with aluminum ions. Therefore, the nanoparticles can be used simultaneously for corrosion sensing and protection.