Emulsion polymerization techniques

Multistage emulsion polymerization techniques are usually applied for (1) the synthesis of large uniform latex particles, (2) the introduction of functional groups into the uniform latex particles, or (3) the synthesis of macroporous uniform latex particles. 

Multistage emulsion polymerization has been proposed by Ugelstad et al. [108,109] for the synthesis of large uniform latex particles. In general, the multistage emulsion polymerization techniques include two main... 

Hydrophobic polymers with some hydrophilic groups can be obtained with an emulsion polymerization technique. Suitable monomers are nitrogen-containing acrylics and methacrylics allyl monomers such as dimethylamino-ethyl methacrylate, dimethylaminopropyl methacrylamide, diethylamino-ethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate and nitrogen-containing allyl monomers (e.g., diallylamine and N,N-diallyl-cyclohexylamine) [225,226]. 

Another application of microparticle technology is the production of polymeric microspheres, which are usually produced by emulsion polymerization techniques. But a variety of polymer colloids can be made by aerosol techniques (Partch et al, 1983 Nakamura et al, 1984 Partch et al, 1985). One advantage of the aerosol route is that larger sizes can be attained... 

Many water-soluble vinyl monomers may be polymerized by the emulsion polymerization technique. This technique, which differs from suspension polymerization in the size of the suspended particles and in mechanism, is widely used for the production of a number of commercial plastics and elastomers. While the particles in the suspension range from 10 to 1000 nm, those in the emulsion process range from 0.05 to 5 nm in diameter. The small beads produced in the suspension process may be separated by filtering, but the latex produced in emulsion polymerization is a stable system in which the charged particles cannot be recovered by ordinary separation procedures. 

ABS products with high impact strengths and relatively high surface gloss may be produced by using traditional emulsion polymerization techniques. 

A serious drawback of solution polymerization is the need to remove the residual solvent. This problem is also present in emulsion polymerization techniques, where the water must be removed and moreover cleaned. 

Grafting by chain transfer initiation has been carried out not only in homogenous medium but also by emulsion polymerization techniques, where the monomer and the catalyst are added to a latex containing the original backbone polymer (99). The efficiency of grafting increases with an increase of temperature of polymerization and with an increase of initiator concentration (generally potassium persulfate) these results indicate not only that the chain transfer reaction has a higher activation... 

More attractive than this capillary tube method seems to be the emulsion polymerization technique, as suggested by Dunn and Mel-... 

Core-shell polymers were commercially introduced as impact modifiers for poly(vinyl chloride) PVC, in the 1960s. They are produced by a two-stage latex emulsion polymerization technique (Cruz-Ramos, 2000). The core is a graftable elastomeric material, usually crosslinked, that is insoluble in the thermoset precursors. Typical elastomers used for these purposes are crosslinked poly(butadiene), random copolymers of styrene and butadiene,... 

Polyvinylacetate (PVAc) has not been used in the pharmaceutical held until recently. During the polymerization, especially at high conversion, free radicals are transferred to dead polymers, resulting in the formation of branched polymers. These branched polymers are susceptible to deterioration. Because the PVAc latex particles are produced by an emulsion polymerization technique, this provides a good process for the water-based dispersion in him coatings. The main purpose of this polymer is the him coating of sustained release dosage forms. The polymer is used as a precursor in the production of polyvinylalcohol (PVA), which cannot be prepared directly by polymerization due to the unstable, isomeric monomer of acetaldehyde. 

As polymeric model fillers with specific surface groups and narrow size distribution, different microgel types, e.g., poly(styrene)-microgel, PS(m), and poly(methoxy-styrene)-microgel, PMS(m), are applied. They can be prepared by emulsion polymerization techniques as described, e.g., in [48]. 

All latex IPN s were synthesized by two-stage emulsion polymerization techniques (1 18) as follows To 300 ml of deionized deaerated stirre 3 waTer at 60°C were added 50 ml of a 10% (W/V) solution of sodium lauryl sulfate followed by 5 ml of a 5% (w/V) solution of potassium persulfate. The calculated quantity of comonomer was added at a rate of about 2 ml per minute. When the first monomer was fully added a minimum of one hour was allowed to elapse. Then a new portion of initiator was added but no new soap followed by the second charge of comonomers under similar reaction conditions. 

It was also shown that stable latexes of high solid content, and small particle size could be practically obtained by this emulsion polymerization technique. Such microlatexes based on acrylic polymers modified by polyesters are an interesting approach to waterborne coatings leading to high gloss paint films (9). 

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. 

Emulsion polymerization typically refers to the polymerization of a nonaqueous material in water. The polymerization of a water-soluble material in a nonaqueous continuum has been called inverse emulsion polymerization. The inverse emulsion polymerization technique is used to synthesize a wide range of polymers for a variety of applications such as wall paper adhesive, waste water fiocculant, additives for oil recovery fluids, and retention aids. The emulsion polymerization technique involves water-soluble polymer, usually in aqueous solution, emulsified in continuous oil phase using water in oil emulsifier. The inverse emulsion is polymerized using an oil- or water-soluble initiator. The product is a colloidal dispersion of sub-microscopic particles with particle size ranging from 0.05 to 0.3 pm. The typical water-soluble monomers used are sodium p-vinyl benzene sulfonate, sodium vinyl sulfonate, 2-sulfo ethyl acrylate, acrylic acid, and acrylamide. The preferred emulsifiers are Sorbitan monostearate and the oil phase is xylene. The proposed kinetics involve initiation in polymer swollen micelles, which results in the production of high molecular weight colloidal dispersion of water-swollen polymer particles in oil. 

Sample Materials. Vinnol H 60d. Vinnol Y 60, and Vinnol E 6Qg are commercial polyvinylchlorides from Wacker. produced by suspension, bulk, and emulsion polymerization techniques, respectively. All materials have nearly the same molecular weight distribution (MWD) as Solvlc 226 which, (with our SEC calibration) gave M = 74.000, M = 35,000. The samples used in this investigation in the Vinnol 60 series had molecular weights in the range M = 72,000 2000 and... 

Polymer processing can be of several types, including free radical, cationic, anionic, metal complex, or metal oxide catalyzed, as mentioned earlier [5], Polymers can be made by bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization techniques [5], The automotive chemist or design engineer working for an OEM should be aware of these various manufacturing processes, which polymers are made by which process, and what characteristics can be expected from the type of process. 

Dispersion or plastisol resins are made exclusively by emulsion polymerization techniques. A vinyl latex is a colloidal suspension (emulsion) of the homo-copolymer particle in water. (The 0.2 )jm average particle size is small enough to be in Brownian movement.) Soaps are generally used to form a protective colloid around the particle, and they are surrounded by a negative electrical charge. In some cases air-dry film-forming systems are possible. 

Wu and Zhao studied LIPN systems by a two stage emulsion polymerization technique [Wu and Zhao, 1995]. A latex seed (polymer 1) was synthesized first by a semi-continuous emulsion polymerization process, swollen by the second... 

The mechanical stability of polymers was related to the polymer s conformation in some of the earlier drag-reduction studies. Above a critical stress, degradation was faster the more contracted and entangled the polymer s conformation (5-7). In petroleum applications the mechanical instability of synthetic relative to carbohydrate polymers was well-recognized. The relative stability problems (possibly related to DUEVs (8)) encountered in the use of high molecular weight hydrolyzed poly(acrylamide) (HPAM) led to the development of an inverse-emulsion polymerization technique (9). (Current research directions using this technique are discussed in Chapter 9.)... 

The manipulation of various emulsion polymerization techniques assists in developing poly(vinyl acetate) latices with specific characteristics needed for certain end-uses. Some of these are summarized in Table XVIII. 

Soluble PVBTMA Cl is prepared in two steps using an emulsion polymerization technique [39], The ionenes and soluble PVBTMA Cl give clear solutions and no solubility problem of these supports occurs, according to the authors. The water-insoluble DTBP is oxidized by O2 gas dissolved in the aqueous phase, where the supported metallophthalocyanine tetrasulfonate is found. The ionenes and polymers used in the reaction mixtures serve not only as a support for the catalysts, but also attract the DTBP due to their organic nature, being of utmost importance for the mass-transfer step of the reaction. Accordingly, the conversions of the reaction were higher for the supported catalysts than for unsupported ones. Polyelectrolyte-... 

Various dispersions are available which even in umnodified form exhibit aggressive tack and good adhesion, especially to polar substrates. Produced by conventional emulsion polymerization techniques, the tack, peel, and shear properties of these dispersions can be varied within wide limits by the choice of monomers. A dispersion will usually consist of at least two monomers, one of high glass transition temperature T and the other with a low Tg value, and the ratio of the two will determine the final properties of the film. Table 1 lists the Tg values of monomers in common use. 

The emulsion polymerization technique is a heterophase polymerization technique in which three phases can be distinguished the water phase, the latex particle phase and the monomer droplet phase (the latter is usually present during part of the polymerization reaction). The product of an emulsion polymerization is a latex a submicrometer dispersion of polymer particles in water. Non-aqueous dispersions of latex particles also exist. 

The emulsion polymerization technique usually contains a micelle-forming surfactant and a water-soluble initiator in combination with a water-insoluble monomer. Polymerization takes place in the monomer-swollen micelles and latex particles. Therefore, the term emulsion polymerization is a misnomer the starting point is an emulsion of monomer droplets in water, and the product is a dispersion of latex particles. In the case of microemulsion polymerization, the monomer droplets are made very small (typical particle radius is 10-30 nm) and they become the locus of polymerization. In order to obtain such small droplets, a co-surfactant (e.g. hexanol) is usually applied. A microemulsion is thermodynamically stable... 

One of the first major applications of latex was the replacement of natural rubber latex by synthetic rubber latex during the Second World War. From there, a continuing interest in the preparation of lattices has evolved. At the end of the twentieth century, environmental aspects are starting to play a role in the further introduction of emulsion polymerization techniques, replacing solvent-based polymerization processes. 

From a synthetic point of view, emuision poiymerization is not suitabie for all monomers. For monomers that are highly water-soluble or, on the other hand, almost insoluble in water, the standard emulsion polymerization technique is not suitable. For water-soluble monomers, besides emulsion polymerization, aqueous phase polymerization can also occur, in which case one could resort to inverse emulsion polymerization, whereby water droplets containing the monomer are polymerized in an oil phase. 

Although some papers on encapsulation of inorganic particles can be found before 1980, most of the early work begins in the mid-1980s and, on average, about 50 papers per year were published on the topic of encapsulation using the emulsion polymerization technique. 

Emulsion polymerization technique is used to manulac-ture several commercially important polymers. Many of these polymers are used as solid materials and must be isolated from the aqueous dispersion after polymerization. In other cases, the dispersionitself is the end product A dispersion resulting from the emulsion polymerization technique is often called latex (especially if derived fiom a synthetic rabber) or an emulsion (even though emulsion strictly speaking refers to a dispersion of an immiscible liquid in water). 

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