Miniemulsion inverse

Fig. 6. a Mixing of two inverse miniemulsions, one containing Murexid solution, the other one Ni(N03)2 b Mixed miniemulsion of b during the process of ultrasonication... 

Nevertheless, for inverse miniemulsions the surfactant is used in a very efficient way, at least as compared to inverse micro emulsions [47,48] or inverse suspensions [49] which are used for subsequent polymerization processes. Again, the surface coverage of the inverse miniemulsion droplets with surfactant is incomplete and empty inverse micelles are absent. Again this is important for the interpretation of the reaction mechanism. 

Fig. 11. Hydrophilic polyacrylamide particles obtained in inverse miniemulsion polymerization in IsoparM...

As compared to classical inverse heterophase polymerization techniques such as polymerization in inverse micro emulsions [47] or dispersion polymerization [75,76], polymerization of inverse miniemulsions is favored by the very efficient use of surfactant and the copying process from the droplets to the par-... 

Fig. 22a,b. Particles obtained in an inverse miniemulsion process consisting of a Zr0Cl2.8H20 b Wood s metal... 

As a new approach to the preparation of water-soluble polymers in inverse miniemulsions, a redox initiation system consisting of ceric ions and carbohydrate-based surfactant Span 60 as a reducing agent has been successfully used for the... 

Fig. 3 TEM micrograph of polyacrylamide (left) and poly(acrylic acid) (right) nanoparticles as obtained by the inverse miniemulsion process...

As a different approach, preformed hydrophilic polymers in aqueous solution can also be used for the miniemulsification process. In this case, the formulation process should be carried out in an inverse miniemulsion with a hydrophobic continuous phase. In order to obtain microgel nanoparticles, the polymer chains have to be crosslinked in the inverse miniemulsion prior to the transfer to an aqueous continuous phase. As a nice example, gelatin has been used for the formation of microgel nanoparticles [4],... 

Fig. 4 The inverse miniemulsion process for synthesis of crosslinked gelatin nanoparticles (for details see text) [4]...

For the formulation of hydrophobic nanoparticles, hydrophobic HPG was dissolved in chloroform and then this solution was miniemulsified in water using SDS as surfactant (see Fig. 6a). The crosslinking reaction was performed by CUSO4 and sodium ascorbate. Hydrophilic nanoparticles of the hyperbranched polymer were obtained in an inverse miniemulsion system by dissolving the polymer in DMF and miniemulsifying the solution in cyclohexane using the block copolymer P(E/B-fc-EO) as surfactant (see Fig. 6b). After the crosslinking reaction performed at 80°C, the obtained particles could be transferred into an aqueous phase. 

Fig. 6 (a) Procedure employed for the formation of hydrophobic nano particles carried out in direct miniemulsion (i) the hyperbranched polymer dissolved in CHCI3 is miniemulsified in continuous phase consisting of H2O and SDS, (ii) catalytic amounts of CUSO4 or sodium ascorbate are added, and the reaction mixture stirred for 3 h at 60°C, followed by reaction for 16 h at room temperature. (b) Procedure employed for the formation of hydrophilic nanoparticles carried out in inverse miniemulsion (i) the hyperbranched polymer dissolved in DMF is miniemulsified in a continuous phase consisting of cyclohexane and P(E/B- -EO) as surfactant, followed by reaction at 80°C for 16 h [116]... 

It could be shown that miniemulsion polymerization is a very suitable method for synthesis of amphiphilic copolymer of high homogeneity and for control of the primary sequence [117], Both direct and inverse miniemulsions can be formed by placing the same monomers in the dispersed or continuous phase, reciprocally. The high interfacial area of miniemulsions is expected to stimulate the change of the growing radical from one phase to the other and, therefore, the formation of copoly-... 

The polymerization process of two monomers with different polarities was carried out in direct or inverse miniemulsions using the monomer systems AAm/MMA and acrylamide/styrene (AAm/Sty). The monomer, which is insoluble in the continuous phase, is miniemulsified in the continuous phase water or cyclohexane in order to form stable and small droplets with a low amount of surfactant. The monomer with the opposite hydrophilicity dissolves in the continuous phase (and not in the droplets). Starting from those two dispersion situations, the locus of initiation (in one of the two phases or at the interface) was found to have a great influence on the reaction products and on the quality of the obtained copolymers, which can act as hydrogels. 

In the AAm/MMA system, the best copolymer with respect to low content of homopolymers, low blockiness, and good redispersibility in polar and nonpolar solvents was obtained in inverse miniemulsion with initiation in the continuous phase cyclohexane (see Fig. 7). In this case, the MMA chains grow in the continuous phase until they become insoluble and precipitate onto the AAm droplets, which enable the radicals to cross the interface. AAm units can then be added to the polymer chain. 

Fig. 7 Copolymerization of hydrophobic (MMA) and hydrophilic (AAm) monomers in inverse miniemulsions with MMA dissolved in the continuous phase in order to obtain a copolymer with low content of homopolymers, low blockiness, and good redispersibility in polar and nonpolar solvents (left). I and signifies a free radical at the initiator molecule and in the end of the polymeric chain, respectively. TEM image of the copolymer nanoparticles (right) [117]...

In another approach, the polymer is precipitated from the continuous phase onto on stable nanodroplets in an inverse miniemulsion [109], In this case, a miniemulsion with the liquid core material is formed in a continuous phase that consists of a mixture of a solvent and a nonsolvent for the polymer. That way, PMMA nanocapsules encapsulating an antiseptic agent could be produced. 

As a third possibility, nanocapsules in a miniemulsion system could be achieved using different interfacial reactions in inverse miniemulsions. The formation of polyurea, polythiourea, and polyurethane nanocapsules synthesized through the polyaddition reaction has been described in detail [110-112], The size of the nanocapsules could be controlled by the amount of surfactant used and the addition time of the diisocyanate. The wall thickness was adjusted by the amount of employed monomers. dsDNA molecules were successfully encapsulated into poly-butylcyanoacrylate (PBCA) nanocapsules by anionic polymerization, which took place at the interface between the miniemulsion droplets and the continuous phase [113]. 

The crosslinking of starch at the droplet interface in inverse miniemulsion leads to the formation of hydrogels. The formulation process for the preparation of crosslinked starch capsules in inverse miniemulsion is schematically shown in Fig. 10. The influence of different parameters such as the amount of starch, surfactant P(E/B-fe-EO), and crosslinker (2,4-toluene diisocyanate, TDI) on the capsule size and stability of the system were studied. The obtained capsules were in a size range of 320-920 nm. Higher amounts of starch and surfactant result in a smaller capsule size. The TEM images of crosslinked starch capsules prepared with different amount of crosslinker (TDI) are presented in Fig. 11. The nanocapsules can be employed as nanocontainers for the encapsulation of dsDNA molecules with different lengths [114] and for the encapsulation of magnetite nanoparticles. 

Fig. 10 Preparation of crosslinked starch capsules in an inverse miniemulsion...

Landfester K, Willert M, Antonietti M (2000) Preparation of polymer particles in nonaqueous direct and inverse miniemulsions. Macromolecules 33(7) 2370-2376... 

Rosenbauer E-M, Landfester K, Musyanovych A (2009) Surface-active monomer as a stabilizer for polyurea nanocapsules synthesized via interfacial polyaddition in inverse miniemulsion. Langmuir 25(20) 12084-12091... 

Baier G, Musyanovych A, Dass M, Theisinger S, Landfester K (2010) Crosslinked starch capsules prepared in inverse miniemulsion as nanoreactors for dsDNA and polymerase chain reaction. Biomacromolecules 11 960-968... 

Also aiming at biomedical applications are nanoscaled hydrogels, prepared in inverse miniemulsion. In crosslinked poly(oligo(ethylene glycol) monomethyl ether methacrylate) (POEOMA) nanogels hydrophilic dyes as the polymeric dye (rhodamine isothiocyanate (RITC) dextran) [41], rhodamine in combination with the drug doxorubicin [42] or gold nanoparticles with bovine serum albumin [43] could be encapsulated. 

PMAA- or citrate-coated magnetite [160] or citrate-coated maghemite [162] nanoparticles could successftiUy be encapsulated in a crosslinked polyacrylamide matrix using an inverse miniemulsion process. Here an inert hydrocarbon (cyclohexane or dodecane) was used as continuous phase and SpanSO as stabilizer. 

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