Controlled Release from Polyurethane Nanocapsules via pH-, UV-Light- or Temperature-Induced Stimuli

Polyurethane nanocapsules consisting of an aqueous core and a polymeric shell with included azo bonds as obtained via interfacial polyaddition of the monomers toluene-2,4-diisocyanate (TDI) and an azo-containing containing diol (VA-060) in inverse miniemulsion allow the selective release of encapsulated material by stimuli such as temperature, UV light, or pH change. The capsule degradation was detected by measuring time-dependently the fluorescence intensities of the dye sulforhodamine SR101, which is dissolved as the fluorescent marker in the core, by exposing the capsules to the different stimuli. Furthermore, the capsules were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The main components during the capsules' degradation were determined via nuclear magnetic resonance (NMR) spectrometry exemplary directly on the azo-monomer VA-060. The results present proof-of-principle studies of different controlled releases with a prototype of polyurethane capsules using the fluorescence dye sulforhodamine SR101 as a model system.