Preparation of polyurea microcapsules with different composition ratios: structures and thermal properties

Polyurea microcapsules were prepared by emulsion polymerization after adding an aqueous solution of poly(vinyl alcohol) as protective colloid to an organic solution of migrin oil as the core substance with aliphatic isophorone diisocyanate (IPDI) and aromatic 2,4-toluene diisocyanate (TDI) as wall-forming materials. Diisocyanate types were investigated for their effects on mean particle size, size distributions and thermal properties. Mean particle size decreased and the size distribution narrowed with the concentration of aliphatic IPDI in the wall. This was deemed to be due to the inferior reactivity of aliphatic IPDI with active hydrogen in water compared to aromatic TDI. Microcapsules from TDI alone in the wall had a broader and larger melting transition at 300-350 degrees C whereas those from IPDI alone showed higher thermal stability. (C) 1999 Elsevier Science S.A. All rights reserved.