Polyurea microcapsules

Ramarao C, Ley SV, Smith SC, Shirley IM, DeAlmeida NJ (2002) Encapsulation of palladium in polyurea microcapsules. Chem Soc Chem Commun 1132-1133... 

Kobaslija M, McQuade DT. Polyurea microcapsules from oil-in-oil emulsions via interfacial polymerization. Macromolecules 2006 39 6371-6375. 

Polythiophenes, with ferrocene groups, 12, 305 Polyurea microcapsules, Pd-containing, 12, 713-714 Poly(vinylcymantrene), synthesis, 12, 311 Poly(vinylferrocene), preparation and properties, 12, 301 Polyynes... 

Polyurea Microcapsules Imperial Chemical Industries, Ltd., Bracknell Berkshire England Stauffer Chemical Co. Richmond, CA X X... 

An approach to immobilization which has recently become popular is microencapsulation in polymers, such as polystyrene and polyurea, developed by the groups of Kobayashi [34] and Ley [35], respectively. For example, microencapsulation of palladium salts or palladium nanoparticles in polyurea microcapsules... 

Hong K, Park S (2000) Polyurea microcapsules with different structures preparation and properties. J Appl Polym Sci 78(4) 894-898... 

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. 

FIGURE 5.84 Flow chart of the process of preparation of polyurea microcapsules. (After Takahashi, T., Taguchi, Y.,... 

Both interfacial polycondensation and polyaddition involve two reactants dissolved in a pair of immiscible liquids, one of which is preferably water, which is normally the continuous phase, and the other one is the dispersed phase, which is normally called the oil phase. The polymerization takes place at the interface and controlled by reactant diffusion. Researches indicate that the polymer film occurs and grows toward the organic phase, and this was visually observed by Yuan et al. In most cases, oil-in-water systems are employed to make microcapsules, but water-in-oil systems are also common for the encapsulation of hydrophilic compounds. Even oil-in-oil systems were applied to prepare polyurethane and polyurea microcapsules. ... 

Figure 15.2 is a microscope image of the polyurea microcapsule prepared through a similar process. 

Scarfato, P. Avallone, E. lannelli, R De Eeo, V. Acierno, D. Synthesis and characterization of polyurea microcapsules containing essential oils with antigerminative activity. Journal of Applied Polymer Science (2007), 105(6), 3568-3577. 

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. 

Some examples of microencapsulated EO are those reported by Scarfato et al. (2007), in which the polyurea microcapsules containing the EO of lemon bahn, lavender, sage, and thyme with anti-germinative activity were prepared by interfacial polymerization in 0/W annlsion. 

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. 

By this method, it was feasible to produce polyurea microcapsules continuously. Due to measuring problems concerning drop size and capsule size, it was not possible to show without doubt that the second micromixer does not change the dispersion. At present, it can only be stated that the impact is small. 

Hirech et al. have described preparation of polyurea microcapsules containing hquid pesticide (e.g., diazinon) suspended in concentrated disinfectant solution, by use of a two-step microencapsulation process [28], The first step is the hquid-hquid dispersion in a Sulzer static mixer (SMX) the second step is microencapsulation by inter-fadal polymerization in a stirred-tank reactor (Fig. 5.4). It has been shown that the... 

Microcapsules with desired release rates according to the application involved can be prepared by incorporating a selected fluid (solvent), while keeping the other capsule parameters constant. These fluids include dearomatized and isoparaffinic hydrocarbons, aromatic hydrocarbons, acetate derivatives, and blends of these [51], In the preparation of polyurethane-polyurea microcapsules containing hep-tenophos (liquid pesticide, b.p. 64 °C), it has been reported that the porosity of microcapsules can be controlled by the addition of 2-ethoxy ethyl acetate or ethyl acetate in the organic phase containing isocyanate prepolymer and pesticide [52]. 

Loading Polyurea microcapsules with monomer/photoinhiator... 

Polyurea microcapsules containing Pd(OAc)2 (Pd EnCat ) have been used in Suzuki-Miyaura cross-coupling processes conducted in either batch or continuous-flow mode. ... 

Interfacial polymerization techniques can be used to prepare robust microcapsules (about 4 pm) that have selectively incorporated functionality such as catalytic groups in their liquid-core domains. The synthesis of these particles is achieved via an oil-in-oil emulsion in combination with interfacial polymerization methods and allows for the encapsulation of substrates not compatible with water-in-oil or oil-in-water emulsion systems (Kobalija and McQuade, 2006). Often these capsules have polyurea shells that can be formed from w/o emulsions containing reactive polyols and isocyanates. This has been very elegantly demonstrated by McQuade and coworkers for the DMAP-catalyzed acylation transformation of an alcohol within the protected environment of polyurea microcapsules formed from reaction of a polyisocyanate and a poly(vinyl alcohol) in the presence of an amine catalyst (Price et ah, 2006 Poe et al, 2007). 

FIGURE 2.84 Flow chart of the process of preparation of polyurea microcapsules. (After Takahashi, T., Taguchi, Y., and Tanaka, M. 2005. /. Chem. Eng. Japan, 38(11), 929. With permission.)... 

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