Water‐compatible, pH‐sensitive, colour‐changing polyurethane with low‐temperature flexibility

A pH indicator (Bromocresol Green, Bromocresol Purple, or Thymol Blue) is grafted onto polyurethane (PU) using 2,2‐dimethylolpropanoic acid (DMPA) to enhance water compatibility. The indicator‐grafted, water‐compatible PU is analysed for soft‐segment thermal, tensile, and shape recovery properties, fast colour change depending on various pH conditions, and low‐temperature flexibility. The PU surface becomes water compatible as DMPA content increases, and the characteristic UV‐vis absorbance is observed for each grafted indicator. The PU series exhibits a sharp increase in tensile stress and crosslink density at low DMPA content, but a decrease with increased DMPA content. The glass transition temperature increases significantly with increased DMPA content. Shape recovery remains high, but shape retention sharply decreases after an indicator is grafted. The grafting of pH indicator onto PU improves the low‐temperature flexibility and imparts an immediate colour change according to the solution pH and grafted indicator.