A CO2-triggered hydrophobic/hydrophilic switchable polyurethane

How to construct a high-performance water-borne polyurethane (WPU) without compromising the properties of traditional solvent-borne PU is a challenging and practical topic. Here we report a CO2-triggered hydrophobic/hydrophilic switchable polyurethane (S-PU) that can regulate its hydrophobicity and hydrophilicity by introducing functional monomer containing tertiary amine group into normal polyurethane chains. By bubbling with carbon dioxide (CO2), the S-PU could be emulsified in water easily and the resulting emulsion displayed high stability (in a sealed vial for more than 120 days at 0–4 °C); On the contrary, by bubbling with inert gas or simply heating, the emulsion could be broken with releasing CO2, so the S-PU flocculated from the water-borne dispersion again. In comparing with a normal water-borne polyurethane, which usually had hydrophilic film surface and showed severe swelling behavior in water, the films of S-PU exhibited excellent water resistance with a lower water absorption (4.50%, 24 h) and higher water contact angle (WCA, 110°). So a new approach to synthesize high-performance WPU was realized, and it could remarkably enhance the practical potential of WPU.