Light and force dual-responsive waterborne polyurethane in multiple states

Light and force-sensitive waterborne polyurethane in multiple states was firstly synthesized and its responsive behaviors were investigated. Di-hydroxyl spiropyran (SP) was prepared and embedded in waterborne polyurethane (WPU) as a chain extender. The SP-WPU showed photo-sensitive properties in both emulsion state and solid state (bulk polymer). The intensity of absorbance at λmax increased as UV (365 nm) irradiation time increased, and decayed when exposed in visible light or in the dark. The SP-WPU emulsion showed a little slower UV activation rate but a much faster decay rate compared with that of SP-WPU film. The SP-WPU emulsion did not show ultrasonic sensitive properties, however, the SP-WPU in the THF/water mixed dispersion showed increasing ultrasonic sensitive properties as water content increased. Moreover, the absorption at λmax of SP-WPU in the solid state increased as elongation increased, especially in the stress stiffening region. The photo-responsive and mechanical responsive waterborne polyurethane could be used as a multi-responsive probe from the solution to the bulk state. It could also provide an environmentally friendly alternative to extend their application in smart coatings and textiles in industry.