Mechanistic elucidation of the molecular weight dependence of corrosion inhibition afforded by polyetherimide coatings

Corrosion of critical metal components exacts a heavy toll in terms of maintenance and replacement costs and damage to ecosystems upon failure. Polymeric barrier coatings protect against corrosion; however, design principles for modulating polymer structure to improve corrosion inhibition remain contested and elusive. Here, we examine molecular-weight-dependent differences in the efficacy of corrosion inhibition on aluminum substrates afforded by polyetherimide (PEI) coatings. Analyses of coated substrates evidence a clear trend denoting improved corrosion inhibition for higher weighted-average molecular weight (MW) PEI. The more rigid and entangled macromolecular network of higher-MW variants exhibit stable impedance values, |Z|0.01 Hz ca. 1010 Ω/cm2, upon extended immersion in brine media, whereas lower-MW variants are readily hydrated and disentangled resulting in a significant reduction in impedance values. Results illuminate mechanistic understanding of molecular-weight-dependence in corrosion inhibition, advance a framework for considering the dynamical evolution of secondary structure, and exemplify generalizable design principles for corrosion inhibition.