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A cysteine derivative-enabled ultrafast thiol–ene reaction for scalable synthesis of a fully bio-based internal emulsifier for high-toughness waterborne polyurethanes

Although tremendous attempts have been made to transform vegetable oils into value-added chemicals, most of the known protocols still require cumbersome preparation procedures for the raw materials, high temperatures, and long reaction times, accompanied with encumbering economic costs and low energy efficiency. In this manuscript, a simple, scalable, and ultrafast method for the synthesis of fully bio-based internal emulsifiers is reported. Flow chemistry was applied to achieve a photo-click, thiol–ene reaction at room temperature by using a cysteine derivative and castor oil as natural raw materials. Conversion rates up to 92.0% were obtained, and the productivity of the internal emulsifier NACCO could reach 360.0 g h−1 with a custom flow chemistry setup. The fully bio-based internal emulsifier was further applied to synthesize waterborne polyurethanes with typical polyols. The bio-content of these waterborne polyurethanes could be as high as 90.0 wt%. Moreover, the films derived from waterborne polyurethanes exhibit superior thermophysical and mechanical properties to known solvent- and petroleum-based polyurethane films. The novel emulsifier, prepared via photo-click thiol–ene chemistry, bridges natural materials (amino acid derivatives and castor oil) and fossil-based products; this affords a green and sustainable strategy for the synthesis of waterborne polyurethanes, which will decrease our chemical dependence on fossil resources.