Polyurea. microcapsule material

For completeness, it should be noted that other groups have also developed encapsulated palladium materials but starting from palladium salts.Palladium-containing polyurea microcapsules have been synthesized and used in... 

Microencapsulation by interfacial polycondensation is a usefiil method to microencapsulate a liquid core material. Especially, polyurea and polyurethane microcapsules have been extensively investigated in various industries [209]. For example, aliphatic hexamethylene diisocyanate (HMDI) and aliphatic ethylene diamine (EDA) have been used to prepare polyurea microcapsules containing insecticide called diazinon [210]. A urea linkage is formed immediately by the reaction between an amine and an isocyanate group (see Figure 4.31), and a polyurea is synthesized by the reaction between an amine with two or more amine groups and an isocyanate with two or more isocyanate groups. 

Li, Z. Chen, S. Zhou, S. Factors affecting the particle size and size distribution of polyurea microcapsules by interfacial polymerization of polyisocyanates. International Journal of Polymeric Materials (2004), 53(1), 21-31. 

Other encapsulations utilize more or less similar methods for the formation of the capsule wall. Complex coacervation utilizes the reaction of an anionic water-soluble polymer with a cationic material to form the shell wall that separates from the solution. As the coacervate separates from the solution, it will tend to coat suspended particles with a protective shell. The shell wall is then hardened with a cross-linking agent. In situ polymerization is used to form urea formaldehyde or melamine formaldehyde shells by using heat to cross-link the monomers forming the shell waU. Interfacial polymerization with isocyanates via hydrolysis is another method to form a shell wall at an organic-water interface. In this case, water acts to hydrolyze some of the polyisocyanate to an amine, which cross-links to form the polyurea microcapsule waU. 

In order to prepare the microcapsule with expected structure, the chosen polymer wall material should match with the core material. The affinity interaction between the polymer wall and the core material can determine the structure of the microcapsule. Highly cross-linked polyurea and polyurethane can form so-called compact capsules with 2-methylbenzothiazole homogeneously distributed in the polymer matrix, while in the case of polyamide core-shell structure capsules were... 

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