Emulsion polymerizations inverse

Dispersed polymers are also produced by inverse emulsion polymerization, miniemulsion polymerization, dispersion polymerization and microemulsion polymerization. 

In this process, an aqueous solution of a water-soluble monomer (e.g., acrylamide) is dispersed in an organic continuous phase using an excess of surfactant. Water-in-oil micelles are formed. The polymerization is initiated by oil-soluble initiators, and the mechanisms involved in this process are similar to those occurring in emulsion polymerization. The product is a dispersion of an aqueous solution of water-soluble polymer in an organic 

When a water-soluble monomer dispersed in a continuous oil phase is polymerized with an initiator soluble in the continuous phase, we speak of inverse emulsion polymerization [159]. This system has all the advantages of emulsion polymerizations (rapid polymerization, high degree of polymeriza- 

Transfer reactions can weaken or even nullify the validity of this statement. 

Inversion emulsion polymerization involves the dispersion and then polymerization of hydrophilic monomers, normally in aqueous solution, in a nonaque-ous continuous phase. The emulsifier systems primarily based on the steric stabilization mechanism (see Section 1.3.3) are quite different from those of the more conventional oil-in-water emulsion polymerization processes. This is simply because the electrostatic stabilization mechanism (see Section 1.3.2) is not effective in stabilizing inverse emulsion polymerization comprising an aqueous disperse phase and a nonaqueous continuous phase with a very low dielectric constant. The unique anionic surfactant bis(2-ethylhexyl) sulfosuc-cinate (trade name Aerosol OT) that can be dissolved in both oil and water 

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Manufacturing processes have been improved by use of on-line computer control and statistical process control leading to more uniform final products. Production methods now include inverse (water-in-oil) suspension polymerization, inverse emulsion polymerization, and continuous aqueous solution polymerization on moving belts. Conventional azo, peroxy, redox, and gamma-ray initiators are used in batch and continuous processes. Recent patents describe processes for preparing transparent and stable microlatexes by inverse microemulsion polymerization. New methods have also been described for reducing residual acrylamide monomer in finished products. 

Fig. 10. Amide end-capped poly(hexafluoropropy-lene oxide) used for the inverse emulsion polymerization of acrylamide in C02 [123]...

In the conventional emulsion polymerization, a hydrophobic monomer is emulsified in water and polymerization initiated with a water-soluble initiator. Emulson polymerization can also be carried out as an inverse emulsion polymerization [Poehlein, 1986]. Here, an aqueous solution of a hydrophilic monomer is emulsified in a nonpolar organic solvent such as xylene or paraffin and polymerization initiated with an oil-soluble initiator. The two types of emulsion polymerizations are referred to as oil-in-water (o/w) and water-in-oil (w/o) emulsions, respectively. Inverse emulsion polymerization is used in various commerical polymerizations and copolymerizations of acrylamide as well as other water-soluble monomers. The end use of the reverse latices often involves their addition to water at the point of application. The polymer dissolves readily in water, and the aqueous solution is used in applications such as secondary oil recovery and flocculation (clarification of wastewater, metal recovery). 

Nonionic surfactants such as sorbitan monooleate yield more stable emulsions than do ionic surfactants, However, the latices from inverse emulsion polymerizations are generally less stable than those from conventional emulsion polymerizations, and flocculation is a problem. 

These superabsorbents are synthesized via free radical polymerization of acrylic acid or its salts in presence of a crosslinker (crosslinking copolymerization). Initiators are commonly used, water-soluble compounds (e.g., peroxodi-sulfates, redox systems). As crosslinking comonomers bis-methacrylates or N,hT-methylenebis-(acrylamide) are mostly applied. The copolymerization can be carried out in aqueous solution (see Example 5-11 or as dispersion of aqueous drops in a hydrocarbon (inverse emulsion polymerization, see Sect. 2.2.4.2). 

The initial rate of polymerization of the inverse emulsion polymerization using sodium di-2-ethyl-hexyl sulfosuccinate (AOT) and sorbitan monooleat (SMO) as emulsifiers and an oil soluble azo initiator can be expressed by [13] ... 

Fig. 11. Inverse-emulsion polymerization of DADMAC. Influence of the monomer concentration on the partition equilibrium of the monomer. (cM)0 initial monomer concentration in monomer/water droplets at equilibrium cM>M monomer concentration in micells at equilibrium) (Data taken from [13])...

Adamsky, F. A. Beckman, E. J. Inverse Emulsion Polymerization of Acrylamide in Supercritical Carbon Dioxide. Macromolecules 1994, 27, 312. 

The formation of coagulum is observed in all types of emulsion polymers (i) synthetic rubber latexes such as butadiene-styrene, acrylonitrile-butadiene, and butadiene-styrene-vinyl pyridine copolymers as well as polybutadiene, polychloroprene, and polyisoprene (ii) coatings latexes such as styrene-butadiene, acrylate ester, vinyl acetate, vinyl chloride, and ethylene copolymers (iii) plastisol resins such as polyvinyl chloride (iv) specialty latexes such as polyethylene, polytetrafluoroethylene, and other fluorinated polymers (v) inverse latexes of polyacrylamide and other water-soluble polymers prepared by inverse emulsion polymerization. There are no major latex classes produced by emulsion polymerization that are completely free of coagulum formation during or after polymerization. 

Glukhikh V, Graillat C, Pichot C (1987) Inverse emulsion polymerization of acrylamide. II. Synthesis and characterization of copolymers with methacrylic acid. J Polym Sci Polym Chem Ed 25(4) 1127-1161... 

The concentrated emulsion polymerization was also applied to an aqueous solution of acrylamide dispersed in decane. Compared to the conventional inverse emulsion polymerization [20], a much smaller amount of organic solvent is employed to produce polymer latexes. 

When the monomer is hydrophilic, emulsion polymerization may proceed through what s called an inverse emulsion process. In this case, the monomer (usually in aqueous solution) is dispersed in an organic solvent using a water-in-oil emulsifier. The initiator may be either water-soluble or oil-soluble. The final product in an inverse emulsion polymerization is a colloidal dispersion of a water-swollen polymer in the organic phase. 

In an inverse emulsion polymerization, a hydrophilic monomer, frequently in aqueous solution, is emulsified in a continuous oil phase using a water-in-oil emulsifier and polymerized using either an oil-soluble or water-soluble initiator the products are viscous latices comprised of submicroscopic, water-swollen, hydrophilic polymer particles colloidally suspended in the continuous oil phase. The average particle sizes of these latices are as small as 0.05 microns. The technique is applicable to a wide variety of hydrophilic monomers and oil media. The inverse emulsion polymerization of sodium p-vinylbenzene sulfonate initiated by both benzoyl peroxide and potassium persulfate was compared to the persulfate-initiated polymerization in aqueous solution. Hypotheses for the mechanism and kinetics of polymerization were developed and used to calculate the various kinetic parameters of this monomer. 

In an inverse emulsion polymerization, an aqueous solution of a hydrophilic monomer is emulsified in a continuous hydrophobic oil phase using a water-in-oil emulsifier. The polymerization is initiated with either oil-soluble or water-soluble initiators. Figure 2 shows a schematic representation of this system. The formation of micelles is uncertain, but is portrayed speculatively. The hydrophilic part of the emulsifier molecule is oriented toward the hydrophilic dispersed phase and the hydrophobic part toward the hydrophobic continuous phase. The initiation of polymerization proceeds by a mechanism analogous to that of the conventional system and submicroscopic particles of water-swollen hydrophilic polymer are generated in the continuous oil phase. 

Figure 2. Schematic representation of an inverse emulsion polymerization...

VANDERHOFF T AL inverse Emulsion Polymerization Initiated Polymerizations... 

Inverse Emulsion Polymerization of Acrylamide in Near-Critical and Supercritical Continuous Phases... 

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