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.
A surface-active monomer, polyisobutylene-succinimide pentamine (Lubrizol U), was used as a stabilizer for synthesizing polyurea nanocapsules with aqueous core via polyaddition at inverse miniemulsion droplet interface. Because of the presence of amine groups in the Lubrizol molecule, it is covalently incorporated into the polymeric interfacial layer after reaction, resulting in more compact (less permeable) capsule shell. The influence of the stabilizer and the monomer concentration on the shell thickness, colloidal stability, average capsule size, and capsule size polydispersity were examined in detail. Different materials, such as a water-soluble fluorescent dye and aqueous dispersion of magnetite nanoparticles with 10 nm in size, were used as inner phase of the polyurea capsules. The encapsulation efficiency was studied using fluorescein as a marker. As an example for biomedical application, the fluorescein-containing capsules were utilized in cell uptake experiments and visualized using fluorescence microscopy.
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