Miniemulsion technique

In the case of inverse systems, hydrophilic monomers such as hydroxyethyl acrylate, acrylamide, and acrylic acid were miniemulsified in non-polar media, e.g., cyclohexane or hexadecane [45,46]. Rather small and narrow distributed latexes in a size range between 50 nmsynthesized with nonionic amphiphilic block copolymers. Depending on the system, the surfactant loads can be as low as 1.5 wt% per monomer, which is very low for an inverse heterophase polymerization reaction and clearly underlines the advantages of the miniemulsion technique. 

In summary, the formation of various gel-type materials using different synthetic routes has been described in this contribution. The advantages of the miniemulsion technique include its versatility in terms of the materials used and the reaction conditions, simplicity of formulation, and high reproducibility. The miniemulsion technique allows one to produce nanoparticles with controlled size and surface properties, which are very important parameters for further application in the area of nanotechnology. 

Jagielski N, Sharma S, Hombach V, Mailander V, Rasche V, Landfester K (2007) Nanocapsules synthesized by miniemulsion technique for application as new contrast agent materials. Macromol Chem Phys 208 2229-2241... 

Whereas the polyketones were usually reported to precipitate from the aqueous phase, under emulsion conditions latexes of ethylene-undecenoic acid-CO ter-polymers and of 1-alkene-CO copolymers can be obtained, which are film-forming at room temperature [12]. Using a miniemulsion technique (cf. Section 6.12.3), water-insoluble diphosphine ligands can be employed without the necessity for hydrophilic modification. 

However, the main focus of the miniemulsion technique lies in the formation of polymeric nanoparticles. Whereas conventional emulsion polymerization can be applied to the formulation of homopolymer latexes by radical polymerization, the generation of copolymer or functional nanoparticles is restricted with this technique,... 

Besides the layer-by-layer technique, which can be applied with or without the use of sacrificial cores [165,166] and usually requires polyelectrolytes, the miniemulsion technique is a highly suitable and versatile method for the formation of capsule formation with sizes down to 100 nm. Even the formation of inorganic capsules (e.g., [167]) by the miniemulsion polymerization is possible. For the formation of polymeric nanocapsules, three general approaches (see Figs. 16, 17, and 23) can be distinguished ... 

Rossmanith R, Weiss CK, Geserick J, et al. (2008) Porous anatase nanoparticles with high specific surface area prepared by miniemulsion technique. Chem Mater 20 5768-5780... 

Musyanovych A, Schmitz-Wienke J, Mailaender V, et al. (2008) Preparation of biodegradable polymer nanoparticles by miniemulsion technique and their cell interactions. Macromol Biosci 8 127-139... 

Co-encapsulation (which is essentially limited to the miniemulsion technique) of a hindered amine acting as radical scavenger improved the photobleaching performance of the encapsulated dye [23]. 

With a modified miniemulsion technique using the encapsulated dye and preformed PS(Mw = 50,000gmor ) as hydrophobic costabilizer, the dyes solvent green, solvent yellow, solvent blue, and solvent red could be encapsulated in a PMMA matrix [27, 28], Depending on the concentration and the dye, phase separation occurred during the generation of the composite particles to form dye crystallites enclosed by a polymeric shell [27]. In the dispersed state, the dyes interact with the polymeric matrix, which is manifested by a small but significant bathochromic shift of the absorption maxima [28]. 

Polyaddition and polycondensation reactions usually lead to functional polymers, since the polymers produced are terminated with reactive functional groups. A higher degree of functionality is easily affordable if monomers with additional reactive groups are used that do not participate in the step-growth polymerization. In emulsion polymerizations, neither polyaddition nor polycondensation reactions can be carried out consequently, the miniemulsion technique is of special interest as no diffusion of the monomers takes place. The first polyaddition in miniemulsion were performed in 2000, with the reaction of polyepoxides and hydrophobic diamines, bisphenols, and dimercaptanes [105]. Stable latexes of epoxy resins could be obtained, and apparent molecular weights of up to 20 000 g mol were measured. 

The advantages of the miao- and miniemulsion techniques compared to precipitation polymerization originate from localization of the reaction volume in very small droplets that actually determine the size of colloidal particles. In such conditions, extremely small nanogels can be prepared and broader spectmm of monomers can be used for polymerization process. Additionally, polymerization in droplets allows loading of microgels with drugs, NPs, or enzymes. 

Koul, V., R. Mohamed, D. Kuckling, H.-J.P. Adler, and V. Choudhary. 2011. Interpenetrating polymer network (IPN) nanogels based on gelatin and poly(acrylic acid) by inverse miniemulsion technique synthesis and chaiactraization. Colloids and Surfaces B Biointerfaces 83(2) 204—213. 

Heterophase polymerization systems can be defined as two-phase systems in which the resulting polymer and/or starting monomer are in the form of a fine dispersion in an immiscible liquid medium defined as the polymerization medium , continuous phase , or outer phase . Even if oil-in-water (o/w) systems are greatly preferred on an industrial scale, water-in-oil (w/o) systems may also be envisaged for specific purposes. Heterogeneous polymerization processes can be classified as suspension, dispersion, precipitation, emulsion, or miniemulsion techniques according to interdependent criteria which are the initial state of the polymerization mixture, the kinetics of polymerization, the mechanism of particle formation and the size and shape of the final polymer particles (Fig. 4.2) [18]. 

Zanetti-Ramos BG, Lemos- Senna E, Soldi V, Borsali R, Cloutet E, Cramail H. Polyurethane nanoparticles from a natural polyol via miniemulsion technique. Polymer 2006 47 8080-7. 

PUs are often used as nanomaterial carriers, but PU-based nanoparticles have also been reported. Most of the nanoparticles have been synthesized by miniemulsion techniques [76]. Miniemulsions are stable aqueous dispersions of oil droplets, which are prepared by high shear of a system containing oil, water, surfactant, and a hydrophobe. 

PU nanoparticles have also been synthesized using several techniques such as suspension-polycondensation [77], interfacial polycondensation and concomitant anulsification [78], suspension polyaddition [79], and dispersion in organic solvent using supercritical carbon dioxide [80,81]. The preparation of PU nanoparticles via miniemulsion techniques was also reported. 

A rather different approach to utilize surface effects for the orientation of smectic elastomers is radical crosslinking of Uquid crystalline polymers using a dispersion or miniemulsion technique in a mixture of solvent and surfactants. CrossUnked smectic-A colloids were prepared in sizes of 100-200 nm showing highly oriented phase structures that could be visualized directly in transmission electron microscopy [107]. 

Yang et al. used the same method to prepare particles from noncrosslinked LC polymers [101]. The shape of the obtained nanoparticles was found to deviate from spherical. Such shape-anisotropic colloids are usually very difficult to produce by miniemulsion techniques. 

Vermes M, Zentel R, Rossle M, Stepputat M, Kolb U (2005) Smectic liquid-crystalline colloids by miniemulsion techniques. Adv Mater 17(17) 2123-2127. doi 10.1002/ adma.200500310... 

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