Heterocyclic group end-capped polyethylene glycol: Synthesis and used as corrosion inhibitors for mild steel in HCl medium

Abstract

In this work, two categories of water-soluble polymeric corrosion inhibitors (CIs) are contributed. These CIs are composed by polyethylene glycol (PEG) middle segment and oleic imidazoline (or thiophene) end groups, respectively labeled as OIM-PEG-OIM and Th-PEG-Th. Two facile synthetic strategies involve epoxy-amino reaction and thiol-acrylate Michael addition were employed. Both Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy verified that a series of target products were successfully obtained. The solution transmittance measurements indicated that with the increase of the PEG segment length, the water solubility of CIs enhanced. And these obtained CIs exhibit somewhat surface activity and could reduce the solution surface tensions to a certain extent. The inhibition efficiencies of these CIs for mild steel in HCl medium were evaluated by weight loss measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). It was found that both OIM-PEG-OIM and Th-PEG-Th show an improved corrosion inhibition efficiency as compared to PEG. And as compared to heterocyclic compounds, introduction of PEG segment showed a negligible influence on their performances. Both CIs can form chemisorption on the metal surface, and the adsorption process follow Langmuir adsorption mechanism. OIM-PEG-OIM exhibit superior inhibition performance and stability as compared to Th-PEG-Th, which can be attributed to the fact that OIM-PEG-OIM bearing two long hydrophobic alkyl end groups. Scanning electron microscope (SEM) observations as well as atomic force microscopy (AFM) measurements also confirmed both OIM-PEG-OIM and Th-PEG-Th could serve as water-soluble CIs for mild steel.