Clays emulsion polymerization

Keywords Clays Emulsion polymerization Iron oxide Metals Organic/ inorganic composite colloids Particle morphology Pigments Quantum dots Silica Surface modification... 

Blending vegetable oils Blending gasoline Clay dispersion Fermentation (pharmaceutical) Suspension polymerization Emulsion polymerization Solution polymerization... 

I. J. Synthesis and characterization of exfoliated poly(styrene-co-methyl methacrylate)/clay nanocomposites via emulsion polymerization with AMPS, Polymer (2003), 44(20), 6387-6395. 

In another interesting development, Yei et al. [124] prepared POSS-polystyrene/clay nanocomposites using an emulsion polymerization technique. The emulsion polymerization for both the virgin polystyrene and the nano composite started with stirring a suspension of clay in deionized water for 4h at room temperature. A solution of surfactant ammonium salt of cetylpyridinium chloride or POSS was added and the mixture was stirred for another 4 h. Potassium hydroxide and sodium dodecyl sulphate were added into the solution and the temperature was then raised to 50 °C. Styrene monomer and potassium persulfate were later on added slowly to the flask. Polymerization was performed at 50 °C for 8 h. After cooling, 2.5% aqueous aluminium sulphate was added to the polymerized emulsion, followed by dilute hydrochloric acid, with stirring. Finally, acetone was added to break down the emulsion completely. The polymer was washed several times with methanol and distilled water and then dried overnight in a vacuum oven at 80 °C. The obtained nanocomposite was reported to be exfoliated at up to a 3 wt % content of pristine clay relative to the amount of polystyrene. 

After the paper making process is complete, latexes that are useful as binders for the application of clays or CaCC>3 to paper for printing paper may be prepared using the dimer of AMS. In a typical formulation, styrene, butadiene, Me methacrylate, and acrylonitrile were emulsion polymerized in the presence of AMS dimer to obtain a copolymer latex.473 Surprisingly, the AMS dimer was used in combination with tert-dodecylmercaptan, so there may have been some residual odor. Unsaturated carboxylic acids, such as acrylic acid, or sulfonic acids, such as 2-ethylsulfonyl acrylate, or unsaturated amides, such as acrylamide, are also useful, providing the polarity necessary in these applications.474... 

Li, H., Yu, Y., and Yang, Y, Synthesis of exfoliated polystyrene/montmorillonite nanocomposite by emulsion polymerization using a zwitterion as the clay modifier, Eur. Polym. J., 41, 2016-2022 (2005). 

The encapsulation of pigment and filler particles is an important area of research, both in the academic world and in industrial laboratories. At present, emphasis is given to the incorporation of clay in polymeric materials, including polymeric nanoparticles. Such systems are expected to exhibit properties other than the sum of the properties of the individual components. In general, several benefits from this encapsulation step can be expected when the obtained particles will be applied in a polymeric matrix (e.g., plastics or emulsion paints) as compared to physical blends ... 

An increased interest in this approach was created when clay encapsulation was attempted. Furthermore, the miniemulsion polymerization technique proved to be another versatile route towards encapsulated materials (see [33]). In the past decade, about 100 papers per year are published (excluding the many papers on clay nanocomposites produced by techniques other than (mini)emulsion polymerization). 

In the past, many groups have tried to encapsulate clay platelets inside latex particles. This encapsulation poses some extra challenges because of the tendency of the clay platelets to form stacks and card-house structures. Most of the attempts resulted in the so-called armored latex particles, i.e. clay platelets in the surface of the latex. Recently, natural and synthetic clays were successfully encapsulated. The anisotropy of the clay resulted in non-spherical latex particles (Figs. 5 and 6), either peanut-shaped [63] or flat [64]. Clay platelets also turned out to be good stabilizing agents for inverse Pickering emulsion polymerizations [65]. 

Fig. 5 Cryo-TEM picture of peanut-shaped encapsulated montmorrilonite. The clay has been edge-modified with a reactive titanate and the surrounding polymer created by a starved-fed emulsion polymerization of methylmethacrylate [63]...

Voorn DJ, Ming W, Van Herk AM (2006) Polymer-clay nanocomposite latex particles by inverse Pickering emulsion polymerization stabilized with hydrophobic montmorillonite platelets. Macromolecules 39(6) 2137-2143... 

Besides properties (which are usually enhanced by adding clay), another crucial factor of PCN materials elaborated through emulsion polymerization is their solid content. Although this point is less frequently addressed, most of the polymer/clay composite latexes reported in literature have solid contents below 20%. However, solid contents between 40% and 60% and sometimes higher are required for industrial applications. Using a seeded semi-batch emulsion polymerization process and a procedure otherwise very similar to that described above for Bentonite,... 

Quite a lot of studies have dealt with the use of organoclays in emulsion polymerization. In most of these studies, the organoclay is dispersed in water and the polymerization proceeds as in conventional emulsion polymerization by monomer diffusion from the droplets to the organophilic clay surface, where propagation of polymer chains takes place. However, in a few examples, the organoclay is dispersed in the monomer phase. This monomer clay suspension is next emulsified (sometimes with the aid of ultrasound to help dispersion and promote clay exfoliation) and the resulting droplets are polymerized [262-267], The latter processes look closer to suspension or miniemulsion (depending on the nature of the initiator) than emulsion polymerization and will not be discussed further. 

A similar strategy involving Laponite or MMT platelets grafted with polymerizable organotitanate and organosilane molecules was recently reported by Voorn et al. [285, 286]. Here, starved-feed soap-free emulsion polymerization of MMA conducted in the presence of the organoclay led to clay encapsulation. However the solid content was quite low (typically around 7%). 

Using an original approach, Zhang and coworkers recently reported the synthesis of PMMA latex particles stabilized by MMT platelets tethered with poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) brushes (Fig. 33) [290]. The PDMAEMA polyelectrolyte brush was synthesized by atom transfer radical polymerization using a cationic initiator previously introduced in the clay galleries. The PDMAEMA-functionaUzed clay platelets were further used to stabilize the emulsion polymerization of MMA initiated by the remaining free radical initiator present on the clay surface. 

Fig. 33 Left Synthesis of ciay-armored PMMA latexes through soap-free emulsion polymerization using PDMAEMA-tethered clay as stabiUzen Right TEM image of the so-obtained PMM A/clay composite coUoid. Reproduced from [290] with permission of Wiley Periodicals...

Recently, a number of groups have also reported the Pickering stabilization of monomer-containing lipid droplets by clays, and their subsequent free radical polymerization [291]. As these articles fall outside the scope of this review, they will not be discussed further. Although not strictly speaking in the scope of the present review, it is also worth mentioning the recent work of Voorn et al. on the first surfactant-free inverse emulsion polymerization stabilized with hydrophobic MMT platelets [292],... 

Chem. Descrip. Sodium 04-12 olefin/maleic acid copolymer Uses Dispersant for dyestuffs, pigments, emulsion polymerization, paints Features High performance in dispersing inorganics such as TiOj and clay in aq. systems... 

There are also some other reports of acrylic resin-clay nanocomposites. A poly(methylmethacrylate) clay nanocomposite was synthesized using a modified organophilic clay in the same manner [8], and by emulsion polymerization [9]. Figure 2 shows a schematic representation of this polymerization method. 

Fang et al [89] have also used Pickering emulsion polymerization (Figure 14.12a) fabricate clay-coated PANI particles by employing exfoliated clay sheets as a stabilizer. PANI particles with a fairly broad size distribution indicate a quite rough surface, which is composed of exfoliated clay sheets (Figure 14.12b). The PANI/clay nanocomposite particles have been employed as an ER material and exhibit similar ER behavior (Eigure 14.12c) to other typical ER systems. 

Montmorillonite (MMT) is natural candidate for formation of nanocomposite due to special lamellar structure. In particular, the absorbed cation in interlayer provides ions exchange ability for intercalation of positive charged aniline monomer in the acid solution. Several approaches have been proposed to attempt to obtain ER active material based on PANI-intercalated MMT (PANI-MMT) nanocomposite [94-96]. Kim et al. [94] have introduced for the first time a kind of PANI-MMT (PANI-Na -MMT) nanocomposites as ER material. PANI-Na -MMT nanocomposite particles have been synthesized via emulsion polymerization. In the preparation, Dodecylbenzenesulfonic acid (DBSA) is used to disperse aniline monomer in xylene and then the clay colloid is added to form emulsion. 

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