Waterborne polyurethanes based on macrocyclic thiacalix[4]arenes as novel emulsifiers: synthesis, characterization and anti-corrosion properties

Abstract

Thiacalix[4]arenes (TC4As) are macrocyclic compounds with a cavity shape, host–guest properties, and modifiable structure for desired application. In this study, two 1,3-alternate derivatives of TC4As were employed as new macrocyclic emulsifiers bearing sulfonate groups in mixture with dimethylolpropionic acid (DMPA) to synthesize waterborne polyurethanes (WPUs). The effect of type and content of TC4As on the particle size, storage stability and viscosity of the dispersions was studied. Moreover, ATR-FTIR, ¹HNMR, XRD, SEM, TGA and DMTA analysis were used to investigate the structure, morphology and thermo-mechanical properties of polyurethane films derived from synthesized WPU dispersions. The morphological inspection of samples exhibited that the microphase separation degree strongly depends on the type and content of TC4As. Furthermore, water contact angle measurements confirmed that the WPUs containing TC4As have higher hydrophobicity in comparison to WPU samples containing only DMPA as emulsifier. This improvement in hydrophobicity of TC4As-based WPUs can be explained in terms of the more hydrophobic structure of the TC4As compared to DMPA. The anti-corrosion performance of the WPUs as environmental friendly coatings for mild steel in 3.5% NaCl solution was also evaluated using PDS and EIS techniques. The results revealed that the sample including macrocyclic SuTC4A as 5 mol% of total emulsifiers has the best corrosion protection ability which was also affirmed by SEM analysis.