| 摘要 |
In accordance with a preferred embodiment of this invention, an active agent, such as a catalyst or a cocatalyst, is encapsulated in a dual-walled microcapsule. Both walls of the microcapsule are polymerization reaction products and both are formed in one basic process. The active agent is initially dissolved in a slowly polymerizing liquid monomer mixture such as a solution of toluene diisocyanate and a polyoxyalkylene polyol. The "monomer solvent" and the active agent combination is selected so that the active agent is nonreactive but soluble in the liquid monomer and insoluble in the polymer formed therefrom. However, before the active agent precipitates, the solution is dispersed in a nonreactive medium and the outer polymeric wall is formed by vigorously stirring the dispersion and then adding a reactive polyfunctional monomer. This polyfunctional monomer, which preferably has two primary aliphatic amine functionalities in terminal or near terminal positions, such as ethylene diamine, quickly reacts with the isocyanate of the initial monomer solution, via an interfacial polymerization reaction, to form the outer polyurea wall around each bead in the dispersion. Then the active hydrogen functionalities of the urea groups on the inner surface of the outer wall react with a portion of the nonreacted isocyanate functionality to form a biuret linkage between the outer wall and either or both the polymerizing monomer solution and the inner polymer wall which is formed therefrom. This reaction effectively bonds the outer wall to the inner wall as it forms. As the polyurethane polymerization reaction continues, the active agent precipitates and migrates toward the center of the microcapsule, and is thereby isolated and protected by the dual-walled structure which has been formed in one basic operation.
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