Light and force dual-responsive waterborne polyurethane in multiple states

Abstract

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 λ_max 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 λ_max 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.