Permeability of dye through poly(urea-urethane) microcapsule membrane prepared from mixtures of di- and tri-isocyanate

Poly(urea-urethane) microcapsules were prepared by the interfacial polymerization with using mixtures of tri- and di-isocyanate monomers as wall forming materials, and dioctyl phthalate containing an oil-soluble dye as a core material. The time course of the dye release in dispersing tetrahydrofuran was measured as a function of the weight fraction of tri-isocyanate monomer in the total monomer w and the core/wall material-weight ratio g. The dye release curves were well represented by an exponential function C = Ceq(1 − e−t/τ), where C is the concentration of the dye in the dispersing medium, Ceq that at equilibrium state, t the elution time and τ is a time constant. τ increased linearly against w at high g, suggesting controllability of the release rate of microcapsules by varying tri-isocyanate/di-isocyanate ratio.