Functional soybean oil-based polyols as sustainable feedstocks for polyurethane coatings

Abstract

The development of renewable and viable alternatives to petroleum-based polymeric materials is a major challenge to the long-term environmental and waste management issues of the polymer industry. In this study, a technology platform composed of a series of efficient and quantitative thiol-ene reactions for preparing functional and sustainable polyols is proposed. First, a soybean oil (SO)-based polyol with two hydroxyl groups (MSO) was synthesized through a controlled thiol-ene click reaction between SO and 2-mercaptoethanol. Second, other functional groups, such as silane, fluorine or ethylene oxide units, were introduced to the MSO through another thiol-ene reaction between the MSO and thiol-terminated intermediates to afford SO-based functionalized polyols. The thiol-terminated intermediates were obtained using a Michael addition reaction between dithiol- and methacrylate-terminated compounds. Employing silane-modified MSO (SiMSO) as a representative functionalized polyol, preparation of polyurethane (PU) coatings was demonstrated. For comparison, PU coatings with commercially available poly(propylene glycol) (PPG) and MSO were also prepared. The thermal, physico-mechanical and anticorrosion properties of the PU coatings clearly demonstrated that coatings made with the silane groups had a better performance. PU coatings with SiMSO exhibited higher hardness, Tg, and adhesion strength than the PU coatings with MSO and PPG. Notably, incorporation of SiMSO improved the anticorrosion properties of the PU coating in a 3.5 wt% aqueous NaCl solution, probably due to the improved blocking and adhesion properties of the coating on mild steel panel. The present study demonstrates SO-based functional polyols as promising alternatives to conventional polyols to afford PU coatings with desirable properties.