Morphologies and release behavior of polyurea microcapsules from different polyisocyanates

Polyurea microcapsules were prepared by emulsion polymerization after adding an aqueous solution with poly(vinyl alcohol) as protective colloid into an organic solution with migrin oil as core material, 1,4-diamino anthraquinone (DAA) as penetrator, and different molar ratios of isophorone diisocyanates (IPDI) and toluene diisocyanates (TDI) as wall materials. The effects of diisocyanate types on the morphologies and release behavior of the resultant microcapsules were investigated. The transmittance (%) of the completely dissolved microcapsule in dimethyl acetamide (DMAc) by UV/visible spectrophotometer decreased with the content of aliphatic IPDI in the wall by increasing the wall thickness due to its inferior reactivity compared to aromatic TDI. Also in SEM images, these polyurea microcapsules from higher TDI content had rougher surfaces. In conclusion, the release profiles of the microcapsules in extraction solution showed that release rate of DAA depended on the roughness of the microcapsules. (C) 1999 Kluwer Academic Publishers.