Thermochromic behavior analysis of terminated polyurethane functionalized with rhodamine B derivative

A novel "off-on" terminated polyurethane based on the rhodamine B modified dye RhEA was constructed with the polyethylene glycol (PEG) and 1,4-butanediol (BDO) as soft segment, isophorone diisocyanate (IPDI) as hard segment. The RhEA terminated polyurethane turned to red from colorless after 254 nm UV induction accompanying transformation of RhEA from a twisted spirolactam to a planarized ring-opened amide. The intensity of absorbance enhanced as UV induction time increased. And the color of the RhEA terminated polyurethane changed from red turned to light red (45 °C) and colorless (65 °C), reversibly. The RhEA terminated polyurethane showed good thermal stability. The thermochromic cotton fabric was obtained with RhEA terminated polyurethane via flat screen printing and it turned to red from white after 254 nm UV induction. The K/S values decreased nearly 65.8% at 45 °C compared to 40 °C suggesting the thermochromic cotton became light red and it turned to white completely at 65 °C. The lactam ring was still retained during the printing process and the thermochromic cotton fabric possessed thermochromic behavior after UV induction. They can be a promising candidate for developing a flexible sensor to monitor environmental changes.