Emulsion, dispersion and suspension polymerization

Emulsion polymers (latexes) are the most commonly used film formers in the coating industry. This is particularly the case with aqueous emulsion paints that are used for home decoration. These aqueous emulsion paints are applied at room temperature and the latexes coalesce on the substrate forming a thermoplastic film. Sometimes functional polymers are used for crosslinking in the coating system. The polymer particles are typically submicron (0.1-0.5 pm). 

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The three main particle production methods are emulsion, dispersion, and suspension polymerization. In each case, the monomer is mixed with a continuous phase and an initiator. In addition a stabilizer in the form of surfactants may be required. 

Adams, M.E. Casey, B.S. Mills, M.F. Russell, G.T. Napper, D.H. Gilbert, R.G. High conversion emulsion, dispersion and suspension polymerization. Macromol. Chem., Macromol. Symp. 1990, 55/id, 1-12. 

In addition to emulsion, dispersion, and suspension polymerization, there are other industrial heterogeneous polymerization processes (Table 2). Of particular importance are slurry and gas-phase processes for polyolefin production, which are also included in Section 4.32.13. 

In addition to the emulsion polymerization technique, miniemulsion, dispersion and suspension polymerizations also provide versatile routes to polymer encapsulation of inorganic particles. 

This article discusses polymerization reactors where the continuous phase is a solution of a polymer in its own monomer or in a solvent. When the low molecular weight species is primarily monomer, the reaction is a bulk polymerization and when it is a solvent, the reaction is a solution polymerization. This distinction has little practical importance. The important consideration is that a high viscosity polymer solution is the continuous phase and is in contact with the reactor walls and the agitator. In contrast, suspended-phase polymerizations (such as emulsion, dispersion, and suspension) and gas-phase polsrmerizations have a low viscosity continuous phase (see Heterophase Polymerization). 

Applications of microparticles can be found in medicine, biochemistry, colloid chemistry, and aerosol research [48]. Some uses include separation media for chromatographic application, high surface area substrates for immobilized enzymes, standards for calibration, spacers in optical cavities and liquid crystal displays, and three-dimensional microenvironments for cell encapsulation. It should be stressed that even a scaled-up MF synthesis enables generation of a relatively small amount of particles, in comparison with conventional emulsion, dispersions, or suspension polymerizations. Thus, most practical applications of such microbeads should utilize their high-value unique properties, for example, a uniform distribution of sizes and control of morphology, structure, and shape. Therefore, some of the demonstrated applications of polymer microbeads are still in the proof-of-concept stage. 

Free-radical polymerization of alkenes has been carried out in aqueous conditions.115 Aqueous emulsion and suspension polymerization is carried out today on a large scale by free-radical routes. Polymer latexes can be obtained as products (i.e., stable aqueous dispersions... 

Dispersion polymerization involves an initially homogeneous system of monomer, organic solvent, initiator, and particle stabilizer (usually uncharged polymers such as poly(A-vinyl-pyrrolidinone) and hydroxypropyl cellulose). The system becomes heterogeneous on polymerization because the polymer is insoluble in the solvent. Polymer particles are stabilized by adsorption of the particle stabilizer [Yasuda et al., 2001], Polymerization proceeds in the polymer particles as they absorb monomer from the continuous phase. Dispersion polymerization usually yields polymer particles with sizes in between those obtained by emulsion and suspension polymerizations—about 1-10 pm in diameter. For the larger particle sizes, the reaction characteristics are the same as in suspension polymerization. For the smallest particle sizes, suspension polymerization may exhibit the compartmentalized kinetics of emulsion polymerization. 

An intermediate polymerization technique between emulsion polymerization and suspension polymerization has been described. Here, the monomers are first dispersed in water containing a small amount of surfactant and a high molecular weight alcohol to form very small droplets of monomer. The polymerization is effected with a water-soluble free radical initiator, such as potassium per-oxydisulfate (4). 

Several methodologies for preparation of monodisperse polymer particles are known [1]. Among them, dispersion polymerization in polar media has often been used because of the versatility and simplicity of the process. So far, the dispersion polymerizations and copolymerizations of hydrophobic classical monomers such as styrene (St), methyl methacrylate (MMA), etc., have been extensively investigated, in which the kinetic, molecular weight and colloidal parameters could be controlled by reaction conditions [6]. The preparation of monodisperse polymer particles in the range 1-20 pm is particularly challenging because it is just between the limits of particle size of conventional emulsion polymerization (100-700 nm) and suspension polymerization (20-1000 pm). 

In dispersion polymerization, by contrast to emulsion or suspension polymerization, a monomer which is soluble in the reaction medium is polymerized. In analogy to fhe aforementioned types of polymerization, an insoluble polymer is obtained. The reaction is carried out in the presence of non-ionic surfactants or soluble polymers, which can stabilize the polymer particles generated to form a stable latex. Wifh particle sizes of ca. 1 to 15 pm, dispersion polymerization can cover the particle size range between emulsion and suspension polymerization. 

Spherical beads possess better hydrodynamic and diffusion properties than irregularly shaped particles. It is, hence, desirable to apply MIPs in a spherical bead format, especially for flow-through applications. Methods to synthesize spherical polymer beads are often classified according to the initial state of the polymerization mixture (i) homogeneous (i.e. precipitation polymerization and dispersion polymerization) or (ii) heterogeneous (i.e. emulsion polymerization and suspension polymerization). In addition, several other techniques have been applied for the preparation of spherical MIP beads. The techniques of two-step swelling polymerization, core-shell polymerization, and synthesis of composite beads will be detailed here. 

Heterogeneous polymerization can be further divided into emulsion polymerization and suspension polymerization. In both types of polymerization, the monomers are dissolved in the dispersed phase. In suspension polymerization, the initiator is dissolved in the dispersed phase as well and nucleation and growth of the beads take place in the droplets. In emulsion polymerization, on the other hand, the initiator is dissolved in the continuous phase, leading to nucleation and bead growth from the continuous phase. 

Taking into account all of the above mentioned applications, the synthesis of magnetic latex will be discussed in two parts first, the preparation of iron oxide nanoparticles and, second, the preparation of magnetic latex. Depending on the aim of researchers, many polymerization techniques are applied such as suspension, dispersion, emulsion, microemulsion and miniemulsion polymerization in combination with controlled radical polymerization techniques like atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) and nitroxide-mediated radical polymerization (NMP). The preparation of hybrid magnetic latex by emulsion polymerization will be the focus of this review. 

In the last few years, many efforts have been given to the preparation of magnetic latexes in dispersed media using suspension, precipitation, dispersion, emulsion, miniemulsion and microemulsion polymerizations. In this review chapter, the synthesis and functionalization of magnetic core-shell polymer particles in dispersed media have been reviewed with the main focus on emulsion polymerization. 

There are four kinds of polymerization processes bulk, solution, emulsion, and suspension polymerization. As Table 4.7 shows [24], the heat of polymerization of vinyl acetate is high compared to other monomers hence, the control of temperature is difficult in bulk polymerization. In the case of emulsion and suspension polymerization, it is somewhat troublesome to separate dispersed polyvinyl acetate particles from the aqueous medium, and it is necessary to remove the emulsifier and stabilizer completely because these substances induce problems in the process of fiber-making. 

CAS 9003-39-8 EINECS/ELINCS 201-800-4 Uses Film-former, thickener, protective colloid, stabilizer, vise, modifier, suspending agent, and dispersant used for emulsion and suspension polymerizations, cosmetics, adhesives, sealants, paints, coatings, paper, detergents, glass fibers, inks, ceramics, nonpharmaceutical tableting, photographic films hair fixative... 

Uses Wetting agent, dispersant, emulsifier, penetrant, and solubilizer in emulsion and suspension polymerization of vinyl acetate for adhesives, paints, textile, fertilizer, mining, water treatment, fire fighting, cosmetic, food industries food pkg. adhesives, coatings, paper, cellophane, textiles emulsifier in mfg. of food-contact articles defoamer in food-contact paper/paperboard... 

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