Interfacial polycondensation encapsulation in miniemulsion

Oily core polyurethane nanocapsules with a mean diameter of 200 nm were formulated in miniemulsion by interfacial polycondensation. The encapsulation process in miniemulsion was optimized by the choice of the surfactant type (anionic, cationic, or nonionic) and concentration; hexadecane was the costabilizer. Size distribution was studied by dynamic laser light scattering, and potential was also determined. The size distribution appeared relatively narrow. Scanning and transmission electron microscopy experiments attested for the submicrometer size, the spherical shape of the capsules, and a smooth external wall. The thermal properties of the polyurethane wall were determined by DSC and TGA, with a fusion temperature around 40 degrees C, suggesting the presence of defaults in the macromolecular backbone such as irregular bounds of urethane and urea functions. The chemical structure of the polymer wall was studied by C-13 NMR and MALDI-TOF mass spectrometry. Both methods attested for the presence of urethane and urea units in the macromolecular chain. MALDI-TOF experiments allowed the investigation of the microstructure of the polymer wall and proved the presence of urethane and urea homopolymer and urethane-urea copolymer. Although the determination of the molecular weight was not possible because of the high polydispersity of the sample, the mass range was comprised between 500 and 3000 Da, in accordance with the number-average molecular weight determined by size exclusion chromatography (PS standards).