Inverse emulsion polymers

The inverse emulsion form is made by emulsifying an aqueous monomer solution in a light hydrocarbon oil to form an oil-continuous emulsion stabilized by a surfactant system (21). This is polymerized to form an emulsion of aqueous polymer particle ranging in size from 1.0 to about 10 pm dispersed in oil. By addition of appropriate surfactants, the emulsion is made self-inverting, which means that when it is added to water with agitation, the oil is emulsified and the polymer goes into solution in a few minutes. Alternatively, a surfactant can be added to the water before addition of the inverse polymer emulsion (see Emulsions). 

Another system similar to the microbaU is called inverse polymer emulsion. In this case, the polymer used is polyacrylamide (PAM). The inverse PAM emulsion is a W/O type of emulsion. The dispersed phase contains 6.4 to 10.5 million Daltons PAM and 1000 mg/L crosslinkers for a sample product. The external continuous phase is white oil. There is a surfactant interfacial film between the disperse phase and continuous phase, as shown in Figure 5.16. The emulsion is stable at the surface. When it is injected into a target formation, it is inverted into an 0/W type of emulsion under certain temperature and salinity, with the help of a phase inversion agent. Thus, the name inverse emulsion is used. 

Lei, Z.-X., Chen, Y.-M., Chen, Y.-W., Yan, J., Jin, X.-R, 2006. Preliminary results of the pilot test of deep profile control using inverse polymer emulsion. Oilfield Chemistry 23 (1), 81-84. 

Polymer emulsions can be produced by the direct and the inverse emulsion process. The direct emulsion polymerization can be performed in a batch, semibatch and continuous process. 

The polymer emulsions can be concentrated by headng imder vacuum to remove excess water and organic solvent by evaporation [43]. In this method, it is possible to reduce the water down to 2% and to increase the polymer crmtent in the emulsion up to 70% [30]. To be effective flocculants, the polymer emulsions must exhibit excellent freeze-thaw properties [11]. Another important requirement concerns their ability to invert wiA excess water to yield a highly viscous dilute polymer solution used as such for applications. A wetting ageru like a surfactant with a high HLB value (10-14) may be used to facilitate inversion. Typical surfactants are oxyethylated alkylphenols, fatty alcohols or fatty acids. They are added (up to 5% by weight of the total formulation) to water or to polymer emulsion prior to dissolution [22,43]. 

Systems using several initiators in a single polymerization reaction have also been proposed. The basis for this concept is the fact that at low polymer conversion, an acrylamide emulsion is more stable under shear than the monomer-containing emulsion prior to polymerization. Then a dual initiator system is used, with one initiator used at low temperature to start the polymerization, ufrile the second, less reactive initiator is utilized, at S0°C to complete the reaction [16]. In another example, inverse emulsions were polymerized in the presence of a biphase initiator system containing both a thermal oil-soluble initiator and a water-soluble initiator (redox couple). This invention was found to increase reproducibility and to improve the shelf-life of polymer emulsions [17]. 

Figure 7.11. Light-responsive and reversible inversion of emulsion (dodecane/ water+NaNOs). The conductivity measurements indicate the type of continuous phase (conducting water vs. insulating oil) in samples maintained under gentle agitation (stirring bar). The emulsifier contains an azobenzene-modified polyacrylate (n = 5, x=3% in Fig. 7.1) and a temperature-responsive surfactant (C12E4) that in absence of polymer would stabilize inverse emulsion above 24°C. (a) Temperature sweep of the same sample exposed to UV or blue light, (b) Switches of the wavelength of exposure between UV and blue lights at fixed temperature (25°C) at times pointed by arrows.

Gao Q, Wang C, Liu H, Wang C, Liu X, Tong Z (2009) Suspension polymerization based on inverse Pickering emulsion droplets for thermo-sensitive hybrid microcapsules with tunable supracoUoidal structures. Polymer 50(12) 2587-2594... 

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... 

PAA can be prepared using bulk polymerization, aqueous polymerization, nonaqueous polymerization, inverse phase emulsion and suspension polymerization. The precise structure of the resulting PAA chain is dependent upon many factors including the polymerization process and conditions. The tacticity of poly(methacrylic acid), PMA, has been studied using NMR spectroscopy (6). For polymerization of methacrylic acid in methyl ethyl ketone at 60 C gives a polymer with 57% syndiotactic triads. Polymerization at low temperatures gives a more syndiotactic product (6) as does polymerization at high pH (7). 

The formation of polyurethane nanoparticles from inverse nano-emulsions (W/O) has also been achieved. Interfacial polyaddition in inverse nano-emulsion is of special interest since this allows the encapsulation of hydrophilic active materials such as proteins or nucleic acids. Thus, taking advantage of the high reactivity of tolylene 2,4-diisocyanate with water molecules, polyurea lipid nanocapsules with aqueous cores obtained from W/O nano-emulsions and prepared by PIT method were designed. Polymer synthesis occurs by in situ interfacial polymerization after nano-emulsion formation. Volatile oils employed as the continuous phase were removed by evaporation and the nanocapsules were redispersed in water. These nanocapsules could be potentially used for encapsulation of both hydrophilic and lipophilic molecules simultaneously. 

Emulsion polymers must be diluted before use. Dilution allows the emulsion product to invert and converts the polymer to its active state. Proper inversion of emulsion polymers is rapid and effective. Improper inversion of the emulsion polymer can result in... 

Preparation of Polymer Nanocomposites via Inverse (Mini)emulsion Polymerization... 

The first study using inverse Pickering emulsion polymerization to prepare polymer nanocomposites was reported by Voorn et al7 An organoclay, Cloisite 20A (20A) from Southern Clay Company (Gonzalez, TX, USA), was... 

If a linear mbber is used as a feedstock for the mass process (85), the mbber becomes insoluble in the mixture of monomers and SAN polymer which is formed in the reactors, and discrete mbber particles are formed. This is referred to as phase inversion since the continuous phase shifts from mbber to SAN. Grafting of some of the SAN onto the mbber particles occurs as in the emulsion process. Typically, the mass-produced mbber particles are larger (0.5 to 5 llm) than those of emulsion-based ABS (0.1 to 1 llm) and contain much larger internal occlusions of SAN polymer. The reaction recipe can include polymerization initiators, chain-transfer agents, and other additives. Diluents are sometimes used to reduce the viscosity of the monomer and polymer mixture to faciUtate processing at high conversion. The product from the reactor system is devolatilized to remove the unreacted monomers and is then pelletized. Equipment used for devolatilization includes single- and twin-screw extmders, and flash and thin film evaporators. Unreacted monomers are recovered for recycle to the reactors to improve the process yield. 

If either dry powders or inverse emulsions are not properly mixed with water, large lumps of polymer form that do not dissolve. This not only wastes material, but can also cause downstream problems. This is especially tme for paper where visible defects may be formed. Specialized equipment for dissolving both dry polymers and inverse emulsions on a continuous basis is available (22,23). Some care must be taken with regard to water quaUty when dissolving polyacrylamides. Anionic polymers can degrade rapidly in the presence of ferrous ion sometimes present in well water (24). Some cationic polymers can lose charge by hydrolysis at high pH (25). 

Inversion ofMon cjueous Polymers. Many polymers such as polyurethanes, polyesters, polypropylene, epoxy resins (qv), and siHcones that cannot be made via emulsion polymerization are converted into latices. Such polymers are dissolved in solvent and inverted via emulsification, foUowed by solvent stripping (80). SoHd polymers are milled with long-chain fatty acids and diluted in weak alkaH solutions until dispersion occurs (81). Such latices usually have lower polymer concentrations after the solvent has been removed. For commercial uses the latex soHds are increased by techniques such as creaming. 

N. Monfreux, P. Perrin, F. Lafuma, and C. Sawdon. Invertible emulsions stabilised by amphiphilic polymers and application to bore fluids (emulsions inversables stabilisees par des polymeres amphiphiles et application a des fluides de forage). Patent WO 0031154, 2000. 

Inverse emulsification A solution of the polymer within a volatile, water-immiscible organic solvent (or mixture of solvents) or a polymer melt is compounded with a long-chain fatty acid (e.g., oleic acid) using conventional rubbermixing equipment and mixed slowly with a dilute aqueous phase to give a W/O emulsion,... 

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