Thermochromic behaviors of terminated waterborne thermochromic polyurethane with tailored molecular weight

Various molecular thermochromic blocked waterborne polyurethanes have been synthesized via incorporating rhodamine B derivative (RhEA). The effect of molecular weight on the thermal properties, rheological behaviors, and thermochromic properties of the thermochromic polyurethanes were tested. The molecular weight of the thermochromic polyurethanes were tailored in the range of 3317–20,377 by choosing polyethylene glycol (PEG200/600/1000) with various molecular weight as soft segments. The results showed that the thermal decomposition temperature of thermochromic polyurethane with the higher molecular weight was higher. The absorbance of thermochromic polyurethanes gradually increased with the increase of induction time. Additionally, the absorbance of PU-PEG200 was lowest because it had least repetition unit. The thermochromic behaviors of polyurethanes were not affected by the molecular weights. The application performances of synthesized thermochromic polyurethanes in textile printing as a functional colorant were also measured. It was found that the actual lines width of PU-PEG200 were less than the theoretical value and the rate of change was negative. This phenomenon was due to the poor water solubility. The K/S of the printed fabrics with polyurethanes gradually raised with the increase of UV induction time. The thermochromic behaviors of fabrics were also not affected by the molecular weights.