Development of azobenzene-functionalized eco-friendly waterborne polyurethane with halochromic property

An eco-friendly halochromic smart polymer was fabricated via covalently introducing azobenzene moieties into castor oil-based waterborne polyurethane . Infrared spectrum and thermogravimetric analysis have confirmed the successful incorporation of azobenzene moieties into polyurethane chains. The halochromic polymer undergoes color change from yellow to amaranth due to the structure shifting from azo form to hydrazine form at pH < 5, showing a visually detectable color difference with the naked eyes. It is also found that the color is reversible by neutralizing treatment and the switching process can be repeated more than 10 times. This eco-friendly halochromic polymer is expected to prepare wearable and visual pH sensor as environment, health and food monitors.