Cross-linking encapsulants

Complex Coacervation. This process occurs ia aqueous media and is used primarily to encapsulate water-iminiscible Hquids or water-iasoluble soHds (7). In the complex coacervation of gelatin with gum arabic (Eig. 2), a water-iasoluble core material is dispersed to a desired drop size ia a warm gelatin solution. After gum arabic and water are added to this emulsion, pH of the aqueous phase is typically adjusted to pH 4.0—4.5. This causes a Hquid complex coacervate of gelatin, gum arabic, and water to form. When the coacervate adsorbs on the surface of the core material, a Hquid complex coacervate film surrounds the dispersed core material thereby forming embryo microcapsules. The system is cooled, often below 10°C, ia order to gel the Hquid coacervate sheU. Glutaraldehyde is added and allowed to chemically cross-link the capsule sheU. After treatment with glutaraldehyde, the capsules are either coated onto a substrate or dried to a free-flow powder. 

A unique feature of in situ encapsulation technology is that polymerization occurs ia the aqueous phase thereby produciag a condensation product that deposits on the surface of the dispersed core material where polymerization continues. This ultimately produces a water-iasoluble, highly cross-linked polymer capsule shell. The polymerization chemistry occurs entirely on the aqueous phase side of the iaterface, so reactive agents do not have to be dissolved ia the core material. The process has been commercialized and produces a range of commercial capsules. 

Starch derivatives are also used to encapsulate pesticides (qv) in a cross-linked starch—xanthate to improve safety in handling and reduce water leaching losses (51,52). Littie or no pesticide is lost during drying. The encapsulated formulations have excellent shelf life when dry, but when placed in water or soil the pesticide is readily released. 

The most widely used sUicones are polymers of methyl(hydrogen)sUoxane and of dimethylsiloxane. Polydimethylsiloxane is the basic polymer used in sUicone repeUents. If the polymer is terminated with methyl groups it is inert however, if it is terminated with hydroxyl groups, it can be cross-linked. Continuous, durable coatings result from the use of curable blends of polydimethyl siloxane and polymethyl(hydrogen)sUoxane. The sUicone finish encapsulates individual fibers. 

The interfacial cross-linking polymerization has been demonstrated to be a suitable method for the production of xylan microcapsules with high drug encapsulation efficiency. SD-... 

Scheme 5.4 Encapsulation of the amine by cross-linking allows the use of two incompatible catalysts [19],...

Muller, A., Das, S.K., Kogerler, P., Bogge, H., Schunemann, V., Krickmeyer, E. and Preetz, W. (2000) A new type of supramolecular compound molybdenum-oxide-based composites consisting of nanocapsules with encapsulated keggin-ion electron reservoirs cross-linked to a two-dimensional network. Angewandte Chemie-Intemational Edition, 39, 3413-3417. 

Hydrogels are 3D cross-linked polymer networks. They can withstand acid conditions and release the entrapped drug molecules. Purdue University researchers have used a poly[methacrylic acid-g-poly(ethylene glycol)] hydrogel to encapsulate insulin, which could be released by pH trigger. 

FIGURE 4.5 Chromatograms of a-phenylethanol enantiomers nsing (a) SFC and (b) open tubular column GC. Conditions (a) 12 cmx250 p.m ID capillary packed with 5-p.m porous (300 A) silica particles encapsulated with fS-CD polymethylsiloxane (10% w/w) and end-capped with HMDS, 30°C, 140 atm, CO2, FID, 10 cmxl2 p.m ID restrictor, (b) 25 mx250 p.m ID cyano-deactivated capillary cross-linked with fi-CD polymethylsiloxane (0.25 xm df) 130°C He FID. (Reprinted from Wu, N. et al. 2000. J. Microcol. Sep. 12 454-461. With permission.)... 

Our research group has developed a multicatalyst system around an encapsulated amine catalyst (Kobaslija and McQuade 2006) that promotes nitroaUcene synthesis. Like the Royer catalysts, these microcapsules are based on a PEI shell. Unlike that system, however, templating is accomplished with a methanol in cyclohexane ( oil-in-oil ) emulsion in an interfacial polymerization, with the PEI cross-linked... 

Sanji T, Nakatsuka Y, Ohnishi S, Sakurai H. Preparation of nanometer-sized hollow particles by photochemical degradation of polysilane shell cross-linked micelles and reversible encapsulation of guest molecules. Macromolecules 2000 33 8524-8526. 

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