Polymer encapsulant materials

C. P. Wong, Improved Eoom-Temperature Wulconicyed Silicone Elastomers as Integrated Circuit Encapsulants, Polymer Materials for Electronics Applications, American Chemical Society Symposium Series, Washington, D.C., Nos. 184, 171, 1982. 

There are few other examples of the application of interfacial polymerizations for the synthesis of encapsulated polymer materials. There is one notable example from the group of Tanaka, in which microcapsules were formed by interfacial polymerization using an oil-inwater emulsions with limonene oil (Mizuno et al, 2004). This was achieved by dispersing... 

Organic solvents are most commonly used, and encapsulating polymers include ethylcellu-lose, NC, polvvinylidene chloride, polystyrene, polycarbonate, polymethylmethacrylate, polyvinyl acetate and others. Inter facial polymerization produces a polymer such as nylon at the interface between layered solns of two precursor materials such as (in the case of a nylon) a diamine and a diacid (Refs 3 11). If the particle or drop-... 

In general, a wide range of nanocomposite polymer materials are already finding real world applications. Traditional nanocomposites are based on (1) copolymerisation of functional macroorganosilanes and metal alkoxides, (2) the encapsulation of organic components within sol-gel derived silica or metallic... 

Polymers may be induced to encapsulate other molecules by a variety of means (Risch and Reineccius, 1995) as diverse as dipping, spray-drying, extrusion, evaporation, and coacervation each technique has its special applications, strengths, and weaknesses. Advantages in common are the protection and slow release of the encapsulate. In any of the mechanisms, a coagulable polymer precipitates around a core of labile material. Polysaccharides are regular encapsulating polymers (Risch and Reineccius, 1995) acacia gum is particularly efficacious because of its protein content. 

Wong, C.P., "Improved RTV Silicone Elastomers as IC Encapsulants", in Polymer Materials for Electronic Applications, edited by E.D. Feit, C. Wilkins, Jr., ACS Symposium Series, Vol. 184, 171 (1982). 

In the Bell System for bipolar, metal oxide semiconductor (MOS) and hybrid integrated circuitry (HIC), RTV silicone elastomer has proven to be one of the most effective encapsulants for mechanical, moisture and alpha particle protection of the IC devices. This RTV material is also one of a few commercial polymer materials that meet most of the Bell System encapsulant specifications. However, the RTV material occasionally experiences some material variations and creates production problems in IC devices shop coating. ... 

In 1996, Wacker-Chemie-GmbH Co. Ltd in Germany developed an active CD, and immobilized it to the cellulose by dipping and padding. This kind of novel CD could be applied to modify not only the cellulose, starch, gelatin and other natural polymer materials, but also the polyester, polyamide, polypropylene and other synthetic fibers. Therefore, they could be used in different functional materials if treated appropriately. For example, a kind of fiber-CDPs encapsulated squalane was developed in Japan. Despite repeated washing, encapsulated squalane was able to maintain the moisturizing capabilities. 

In this context. Let et al. suggested that the composition of the interface may be more important than the total surface area itself. In recent years, research focused on modification of the oil-water-interface with the aim of physical stabilization of the interface during dehydration and/or modification of the release of the encapsulated core material. A well-described system is stabilization of the interface through bilayer formation using lecithin as emulsifier and chitosan as oppositely charged polymer for bilayer formation. - Due to the cationic surface of the droplet, surface repulsion... 

Polymer coacervation can occur in either aqueous or organic liquids. Coacervation in aqueous liquids and the related processes are mainly used to encapsulate water-immiscible liquids or water-insoluble solid particles. On the other hand, coacervation in organic liquids, or sometimes called phase separation in organic liquids, is used to encapsulate core materials that are not miscible or soluble in the organic liquids. It may be induced by the addition of a nonsolvent to the polymer solution or by the addition of an incompatible polymer based on polymer-polymer incompatibility. This chapter will only discuss the coacervation in aqueous liquids. 

Another method to create hybrid nanoparticles is encapsulation of smaller nanoparticles, such as dendrimers, into larger nanoparticles, such as polymeric nanoparticle and liposomes using a double emulsion method.[36] Double emulsions may be formed with either the water-in-oil-in-water (W/OAV) or the oil-in-water-in-oil types (O/W/O). The W/O/W double emulsion method is more commonly used as it stabilizes the particles in the aqueous phase and encapsulates hydrophilic materials into a variety of polymers or copolymers with a controlled particle size. [37] This method allows for the preparation of hybrid nanoparticles that have two-size scale, i.e., polymeric nanoparticles of 50-200 nm and encapsulated dendrimers or other polymer conjugates of <10 nm).[36,38] The encapsulation process is affected by several parameters such as the chemical composition of the outer layers, size and surface charges of dendrimers, and ratios of the outer and inner nanoparticles. [36,25]... 

Micro-encapsulation of drug-polymer systems using flic RESS (Rapid Expansion of Supercritical Fluid Solutions) techniques have been initiated with limited success due to poor understanding of the complex phenomena involved in co-nucleation of components. Not only do the particles have to be nucleated with the desired particle size and shape but also encapsulate the material simultaneously in an uniform fashion. 

As for animal cell entrapment in hydrogel microparticles or microcapsules, encapsulation procedure should proceed under physiological conditions within a short time (20-30 min), in order to provide cell viability, and to be as simple as possible because all manipulations are carried out under strictly sterile conditions. Taking into account all these requirements, it should be noted that the list of polymer materials and methods for animal cell encapsulation is rather limited. So-called alginate-based carriers (microparticles, micro- and nanocapsules) assure the favorable polymer systems for animal cell immobilization. 

As for polymer materials used for encapsulation of some low molecular weight drugs, such as cytostatics, antibiotics, etc., which are more stable compared with animal cells or biopolymers (DNA, proteins, peptides, etc.), the list of polymer materials used for their encapsulation is more extended. It includes a series of synthetic polymers as well as their copolymers with namral polymers. We could mention polyacrylates, for example, polyaUcylcyanoacrylates [11], polyester-poly(ethylene glycol) [12], poly(epsilon-caprolactone) [13], polyethylenimine-dextran sulfate [14], dextran-HEMA (hydroxy-ethyl-methacrylate) [15]. 

In the swollen state, these capsules were permeable to macromolecules, and this was used for the pH-controUed encapsulation of PAA (Fig. 3.4A), when later reducing the pH [31]. The release of encapsulated polymer is achieved by swelling the filled capsules in alkaline medium, which allows the amount of entrapped material to be measured. This amount can be controlled, and is dependent upon on the initial concentration of the surrounding PAA (Fig. 3.4B). 

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