Miniemulsion ionic polymerizations

Miniemulsion is a special class of emulsion that is stabilized against coalescence by a surfactant and Ostwald ripening by an osmotic pressure agent, or costabilizer. Compared with conventional emulsion polymerization process, the miniemulsion polymerization process allows all types of monomers to be used in the formation of nanoparticles or nanocapsules, including those not miscible with the continuous phase. Each miniemulsion droplet can indeed be treated as a nanoreactor, and the colloidal stability of the miniemulsion ensures a perfect copy from the droplets to the final product. The versatility of polymerization process makes it possible to prepare nanocapsules with various types of core materials, such as hydrophilic or hydrophobic, liquid or solid, organic or inorganic materials. Different techniques can be used to initiate the capsule wall formation, such as radical, ionic polymerization, polyaddition, polycondensation, or phase separation from preformed polymers. 

Ionic polymerizations in heterophase systems have been described very rarely, and are generally considered as unconventional. Nonetheless, the conditions employed for ionic polymerizations in miniemulsions are ideal, as there is no diffusion of the monomers. Ionic miniemulsion polymerizations have been carried out either under mild conditions (e.g., in the presence of water) or in water-free... 

Figure 15.5 Examples of monomers for ionic polymerizations in miniemulsion.

Figure 3.1 Mechanism for interfacial (an)ionic polymerization in a miniemulsion.

The effect of the amount of surfactant SDS, hydrophobe hexadecane, iron oxide magnetic particles, MAA and non-ionic cellulose ether, hydroxyethylcellulose, on the magnetic latex morphology, surface quality and size distribution was studied by Forcada et al. for the encapsulation of magnetic particles by miniemulsion polymerization of St. Optimal conditions were 2-3% of SDS, 9-12% of hexadecane, 10% of iron oxide and 2% of HEC, relative to the total amount of St and iron oxide [177]. 

Glycopolysiloxanes with cellobiose moieties have been used for the sterie stabilization of vinyl acetate miniemulsion polymerization [93]. The first attempts to get stable PVAc nanopartieles by using only the glycosiloxane derivatives as polymer surfactants failed, but stable nanoparticles were obtained using a mixture of glycosiloxane and a non-ionic triblock PEO-Z)-PPO-Z)-PEO copolymer. 

Even in the presence of large amounts of water, the miniemulsion process permits the synthesis of hydrophobic polyesters in a very simple manner and at very low temperatures in order to obtain stable polyester dispersions. The influence of several parameters on the esterification yield has been studied. On the one hand, any modification of the dispersed phase such as the hydrophobicity of the components, viscosity, and the reactant nature results in different yields. With increasing hydrophobicity of the monomers or decreasing viscosity, the yield increases. On the other hand, any modification of the surrounding environment of the droplets such as the interface nature, the ionic strength and the interface area, has no influence on the equilibrium. From a thermodynamic point of view, this polymerization presents the characteristics of a bulk or solution polymerization. Independently of the dispersion state in the range studied, the equilibrium is the same as in bulk or in solution polymerization with an organic phase saturated with water. It is however very unlikely that the reactions occur exclusively in the core of the particle, but in order to provide an answer to this question it would be necessary to conduct a kinetic study related to the interface area. 

Abstract Monodispersed biodegradable poly(n-butylcyanoacrylate) nanocapsules containing DNA molecules (790 base pairs) within an aqueous core were prepared by anionic polymerization of n-butyl-cyanoacrylate at the droplets interface in inverse miniemulsion. The aqueous droplets in the size range of 300-700 nm dispersed in the hydrophobic continuous phase were formulated using the miniemulsion technique that allows an easy control of the droplet size and size distribution. After polymerization, the capsules were transferred into an aqueous phase. The effect of several reaction parameters such as the amount of monomer, type of the non-ionic surfactant (i.e. Span 80 and Tween 80) and type of the continuous phase (i.e. Miglyol 812N and... 

ATRP has been successfully carried out in bulk, in solution [27,28], as well as in aqueous solution [157], emulsion [169], miniemulsion [170], and suspension [135,171], and in other media (e.g., liquid or supercritical CO2 [109] or ionic liquids) [172,173]. Typical temperature range for a polymerization is from sub-ambient temperature to +130 °C. Molecular weights for linear and graft copolymers range from 200 < Mn < 500,000 (however the molecular weight of bottle-brush copolymers and particle tethered copolymers can reach well into the millions), and polydispersities are low, 1.05 < < 1.3,... 

The electrical conductivity of a fluid is a quantitative measure of its ability to carry an electrical current, and therefore depends to a large extent on the concentration of ionic species. Given that the conductivity of pure water is extremely low (limited to 0.0548 xScm" at 25 °C by the HjO dissociation constant into H and OH" when no added ions are present), this technique will be sensitive to changes in ionic concentration. So, while it is not impossible to be used for the online monitoring of solution or melt phase processes, it is better suited for use in emulsion and miniemulsion polymerization reactions where ionic surfactants and initiators are commonly employed. 

Shulai Lu prepared magnetic polymeric composite particles by miniemulsion polymerization of styrene in the presence of hydrophobic magnetic nanoparticles with hexadecane (HD] as hydrophobe, 2,2 -azobisisobutyronitrile (AIBN], and sodium dodecyl sulfate (SDS] as an emulsifier or sodium p-styrenesulfonate (NaSS] as an ionic comonomer [151], The results showed that miniemulsion polymerization is an effective method for encapsulation of magnetite into a hydrophobic polymer. 

Chakraborty S, Jahnichen K, Komber H, Basfar AA, Voit B (2014) Synthesis of magnetic polyst3o-ene nanoparticles using amphiphilic ionic liquid stabilized RAFT mediated miniemulsion polymerization. Macromolecules 47 4186—4198... 

Carboxyl and amino-functionalized latex particles were synthesized [67] by the miniemulsion polymerization of styrene and acrylic acid or 2-aminoethyl methacrylate hydrochloride, and the effect of hydrophilic comonomer and surfactant type (nonionic versus ionic) on the colloidal stability, particle size, and particle size distribution was analyzed. The reaction mechanisms of particle formation in the presence of nonionic and ionic surfactants were proposed. 

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